Saturday, January 29, 2011

Astrophotography, Part 1; Supplemental Post (B) - Photography with Imre - Episode 32

In this supplemental post I'll be discussing photography using telescopes, in contrast to part "A" of this two part text that is focused on photographing the night sky without one.

A Little about Telescopes and Eyepieces
Before getting into the photography side of this topic, let's first take a quick look at the three families of telescopes that I mentioned in the episode. I've only written fairly quick summaries below with the intention of providing you with some overall information. If you are interested in finding out more (and believe me there is a lot to learn about scopes), check out the Web resources section.

Refractors: Refractors are basically your classic telescope style; a tube with an objective at the front and eyepiece at the back. The objective is usually comprised of two or three optical elements, the former design generally referred to as achromatic and the latter as apochromatic. Both designs reduce the effects of spherical and chromatic aberrations, but apochromatic ones are more effective. As such, these versions tend to cost more, but for those with cash to spare and the longing for very good optical quality then they're tough to beat (within reason of course). But it's not like the achromatics are that bad either and are still a great choice for those on lower budgets.

There are some nice advantages to refractors, one being that they are very easy to use and most don't require collimation (alignment of the optics) out of the box as that has been done at the factory. Since there is nothing in the way of light getting into the tube as there is with reflectors and catadioptrics, no diffraction spikes/effects occur so you get lovely tiny round dots for stars (no "X" shapes). On the downside they tend to be quite pricey for their size. Last I checked, a 6" achromatic type is around $2,000 with high-end apochromatic ones (like Takahashi telescopes with fluorite lenses) coming close to or just over the five figure mark. In contrast, a 10" Newtonian reflector on a dobsonian mount is about $1,000. Fast telescopes (e.g. f/7) of this type also tend to exhibit more chromatic aberration than slower ones (e.g. f/16).

By the way, some spotting scopes have the ability to be attached onto cameras; they are basically refractors. I have a couple of these, one of which is this model: Although it doesn't provide outstanding image quality, for its price, it's a ton of fun to play it! I'm digressing...

Reflectors: Unlike refractors, reflectors have no lenses. Instead, mirrors are used to focus incoming light. This has several advantages over using glass (or fluorite) lenses, in that chromatic aberration is no longer an issue as mirrors can focus all frequencies (colors) of light into a single spot. However, for our purposes there are two common types of mirror shapes used in these types of scopes to focus light, one being spherical and the other parabolic. Spherical mirrors suffer from, you guessed it, spherical aberration, which means that parallel rays of light do not get focused into a nice little spot (hence a softer versus sharper image). This is the advantage that parabolic mirrors have, because in their case parallel rays of light are focused into a more precise spot, thus yielding better image quality.

So why are telescopes made with spherical mirrors then if they are inferior to parabolic ones? Well, primarily cost. Spherical mirrors are easier to grind/manufacture and for smaller telescopes, say 5" or less, the effect of spherical aberration isn't as noticeable as it is on larger and faster scopes. I can personally say this is true as I own a 4" Bushnell with a spherical mirror and a 10" scope with a parabolic one, both Newtonian designs. Indeed, the smaller 4" scope actually has very good quality in comparison to what the 10" delivers, aside from the obvious such as more light gathering ability and resolution advantage of the larger one.

Reflectors, such as the common Newtonian (see figure 1; figure 2 shows a closeup of the focuser with an eyepiece in it), are overall quite inexpensive and can produce stunning results, but do have a few disadvantages. Faster scopes of this type, around f/5, have visibly more coma, which makes stars towards the edges of the image look like little comets. This may not be much of an issue if one is just viewing with the naked eye, but photographers might not take well to this artifact. However, this effect can be corrected with various types of eyepieces, an example of this being the 7mm Speers-Waler you see in figure 5. Another matter concerns collimation, the lining up and adjustment of the mirrors/optical elements. Having done this a few times with my scopes, I can comment that it's not very difficult to do, but can be a little time consuming to get it just right. The better the alignment of the mirrors, the better/sharper your image will be, so it's a necessary aspect to such telescopes; there's more information on the art of collimation in the Web resources section below. The last item I'll touch upon is the secondary (aka diagonal) mirror; this mirror held by its four supports (sometimes one on smaller scopes) is affectionately known as the "spider". This smaller mirror, in comparison to the primary, is what redirects light to the eyepiece on the side of the telescope body and blocks a little bit of it from getting into the tube. But this amount of blockage is usually quite minimal, generally a loss of light in the single digit percents. Some photographers may not like the diffraction spikes caused by the spiders "legs". You've surely seen this on some astronomical photographs where stars have "X" like spikes extending out from them. As with most things, this is a personal like or dislike. I don't mind the look of them myself.

Catadioptrics: And now we come to the last type of telescope I'll discuss here. These are very similar to reflectors, but with a couple of slight twists. In regard to similarity, both reflectors and catadioptrics have a primary and secondary mirror, but in catadioptrics the secondary mirror does not reflect light out to the side. Instead, light is funneled back down the tube and through a hole in the primary mirror. As such, the eyepiece holder is at the bottom of the scope. In addition, there is a lens at the front of the scope which plays a role in getting light to focus more accurately off the primary mirror; this is termed "corrector plate" in Schmidt-Cassegrain scopes and "meniscus lens" in Maksutov types. These are very popular scopes as they aren't very expensive, although more than Newtonian reflectors, and they are usually sealed units with the mirrors/optics aligned at the factory, hence requiring minimal maintenance. Overall there are fairly few downsides to catadioptrics. Cost can be seen as one as they are a tad more than reflectors, and the secondary mirror blocks a little light from getting in, but not a major issue.

Again, I'd like to emphasize that there is a great deal more information available about telescopes and if you'd like to find out more, feel free to check out the Web resources section below. Some of the links to go Wikipedia, but after perusing through the articles they seemed to be accurate.

Now for a little bit about eyepieces; figures 3, 4 and 5 show a few of mine. As with telescopes, there are a surprising number of different types out there from simple (and outdated) one lens designs to complex (and usually expensive) multi-element types like Plossls, Erfles and Naglers. In a nutshell, each type has its pros and cons, generally hovering around factors like image quality, field of view and eye relief. Some are also better for looking at dim objects like star clusters or nebulae, others for planetary viewing. There are three common sizes in regard to the eyepiece barrel, the part that slips into the telescope's focuser. Your cheap department store variety of scopes usually have a focuser that can only accommodate 0.965" (24.5mm) eyepieces, whereas many higher quality telescopes you can purchase from dedicated telescope shops accept both 1.25" (31.7mm) and 2" (50.8mm) eyepieces (usually an adapter is needed or is supplied with the scope; see figure 6). My recommendation is that even if you don't have a large budget, at the very least try to get a telescope with a 1.25" focuser, otherwise you may find it difficult down the road to locate good quality eyepieces in the 0.965" size. In addition, those really cheap scopes are exactly that, cheap; you do get what you pay for.

Barlow lenses can be used with eyepieces as they can increase the magnification you can achieve. Common factors include 1.6X (figure 8), 2X, 3X and some are variable (see figure 7). If you're on a budget, Barlow lenses can be a nice way to increase your magnification without requiring additional eyepieces, even if it means some loss of light.

Playing with Numbers
Most of us with telescopes love the fact that we can get massive magnification with them, but it has to be understood that there is a limit. Unfortunately, many department store variety of scopes advertise that their small units can provide ridiculously high values, such as five or six hundred. As far as legal issues go, this is true; put together the appropriate eyepiece with a Barlow lens and there you have it. But in regard to seeing anything useful other than a horribly blurry, faint blob of some sort in your eyepiece, not going to happen. So to roughly find out what a telescope is reasonably capable of in terms of magnification (still yielding a fairly sharp, good quality image), I like to use the following which from experience has proven quite valid: multiply the size of your scope in inches by fifty, then divide by two. So if I use my 10" scope as an example, then (10 X 50) / 2 = 250. For you metric folks out there, you can take the size in millimeters and multiply by two, then divide by two and you'll get nearly the same answer. The "seeing" quality will also affect this, but I've dedicated a section to that topic below.

Ok, so now we have an idea of what the telescope is capable of, but of course you likely won't always be using your peeper tube at this level of magnification. Many night sky areas are just gorgeous with a wide field eyepiece that provides very little magnification, like under 50. Therefore, to find out what level of magnification you're getting with a particular eyepiece, simply divide the focal length of the scope with the focal length of the eyepiece. My 10" Newt has a focal length of 1,200mm and one of my favorite eyepieces is 7mm, so 1,200 / 7 = 171. A 28mm eyepiece on the other hand will give me 42.9 times magnification.

Camera Adapters
To begin with, there are actually quite a few different ways that a camera can be attached onto a telescope. When using an SLR (digital or film), you can often find a t-mount adapter for it (see figure 9). These adapters have a mount on one side that attaches to the camera and a threaded side that screws directly onto some eyepieces, an adapter ring on an eyepiece, or onto a camera adapter (see figures 10 and 11). Some camera adapters, like that shown in figure 10, allows a 1.25" eyepiece to be slipped into it (of course not all of this size will fit). If you have a point and shoot model, one of these types of adapters can be used (sorry, I was lazy to take a photo of mine). The camera is screwed onto the small base and that "O" shaped section is tightened around an eyepiece. Then the height and position of the adapter is adjusted so that the lens of the camera is as close as possible to the eyepiece. On point and shoot cameras with larger lenses, don't be surprised if the image shows vignetting. Those cams with tiny fixed (no zoom that is) lenses generally work well, especially with eyepieces that provide large eye relief; many of the images in the episode were taken with such a setup and turned out quite well.

Do-it-yourselfers have also created their own mounts. In fact my old Fuji was in a holder I made out of nothing more than paper, chopsticks as a frame and lots of tape; worked great on the 7mm Speers-Waler. I've also seen old film canisters modified to accept webcams, and you can purchase CCDs made specifically for astrophotography, but I'll let you poke and prod around the Web to find out more about that.

Cool it! "Seeing" what I'm saying?
At this point I could probably get right into photography with a telescope, but you might be a bit disappointed with the results, especially if you aren't familiar with thermally stabilizing your telescope or bringing it to equilibrium with the environment's temperature before using it. "What!?" you say. All it really means is to let your telescope's temperature match the temperature it is outside (usually cool down). For example, there's a scope indoors at room temperature, about 21C (70F), but you want to take it outside where the temperature is only 10C (50F). If you looked through the scope the moment you took it outside, and for a while afterwards, I can best describe the appearance of the image as if it was underwater. This is caused by a couple of factors, one being that the mirrors and/or lenses (depending on the scope you're using) are contracting and deforming as the material looses heat energy. This movement is incredibly small, microscopic, but more than enough to ruin the quality of the image. In addition, as the scope looses heat it causes weak air currents to form, which also degrade the image quality. Reflectors, with their wide open and unsealed tubes, are most prone to this.

The greater the temperature difference, the longer the time it will take for the telescope to reach this equilibrium. I remember taking my 10" Newt outside when it was a chilly -20C (-4F) and it took over two hours for the image to stabilize. Of course in other not so extreme cases this time span decreases to around under 30 minutes.

Now I've already touched upon this a little in part "A", but "seeing" conditions play a big part in not only how well you can see objects through your telescope, but also how photographs will turn out (or not). Upper level winds/turbulence high up in the atmosphere, level of humidity in the air, amount of dust/pollution and light pollution all play a part in adding gunk between you and the stars, planets and other celestial wonders. It's a combination of these things that make stars twinkle, and indeed, less twinkle is usually a good indicator of better seeing. On some days you'll find that you can easily see the dark division in the rings of Saturn, while on other days it's just a bright oval shape... yet seemingly to our eyes the dark night sky may look no different on either occasion.

Anyway, seeing is nice to know about because if you know what to look for it may save you some time and effort. Imagine if you're about to spend around three hours worth of time taking multiple exposures of some faint bodies in the sky, only to discover that waiting a day or two would have resulted in much clearer photographs. One thing I've certainly become accustomed to when working with my telescope is being patient; whether hunting for that dim nebula, focusing carefully or just plain waiting for the camera to finish exposing.

Photography Using a Telescope
In my video I discussed two methods of photography that can be performed with telescopes, but actually there are three (I made little boo boo) and I discuss them in a little more detail below. Since I have experience using digital SLRs in this case, that's what I focus on --just a fair warning that if you're looking for CDD, webcam or film astrophotography material you'll have to do some Googling on your own.

Prime-focus: As mentioned in the episode, you simply attach the camera body directly onto the telescope's focuser without using an eyepiece or any camera lens. Indeed, this basically turns your scope into a huge lens. Although you don't get a lot of magnification, you don't lose a lot of light either as no lenses get in the way. On my 10" scope (1,200mm focal length) I can basically image the full moon, or about half a degree of the sky. This is also a wonderful method to take some wide-field shots.

Eyepiece Projection: To err is human... :P In the video, I said that attaching your camera body to an eyepiece (no camera lens used) is the afocal method. In fact, I messed up on the terminology. When you attach the camera body to a telescope without a camera lens but are using an eyepiece, you are employing the eyepiece projection (aka positive projection) method. The image the eyepiece delivers is projected directly onto the camera's focal plane (the sensor or film). Thankfully though, the photographs of the planets reflected afocal photography, as the Fujifilm FinePix 40i camera I used has a fixed lens and I was taking pictures through an eyepiece.

Afocal: The afocal method is similar to eyepiece projection, but differs in that a "regular" camera lens is attached or you're using a point and shoot model, which of course has the lens built in. For example, an eyepiece is in the focuser and a point and shoot camera or a dSLR with a lens attached is used to capture photographs.

With both the eyepiece projection and afocal methods, you may experience vignetting depending on the eyepiece you use. But unlike prime-focus, you can achieve much higher magnification levels.

To track or not to track?
With a telescope, not only is the image magnified, but so is the movement of the celestial bodies as they pass across the sky. For example, if I'm looking at Jupiter with my 7mm eyepiece, which gives 171X magnification, every 5-10 seconds I have to nudge my Dobsonian mount a little to keep the gas giant in view.

In regard to photography, this means that the use of long exposures will be next to unusable; even shutter speeds around 1/2 second might end up producing a soft image. So if you do not have a tracking mount at your disposal to counteract the earth's rotation, then you need to look for ways to reduce the exposure time. This means doing such things as using the brightest lens you have wide open (if utilizing the afocal method) and bumping up the ISO as high as you dare. Your selection of eyepiece will also play a role in this too, as the higher the magnification gets the darker the image will become. Then you'll likely need to use slower shutter speeds to get reasonably well exposed photos, but the result may be undesirable. Lastly, you'll also very likely be limited to the brightest of objects in the sky; the moon (easiest target, even at high magnification it's still very bright), Mercury, Venus, Mars, Jupiter, Saturn, Uranus, maybe Neptune if you have a large scope, bright stars, some open clusters, and maybe a couple of nebulae (again with a large fast scope).

On the other hand, if you have a tracking mount then long exposures become easier to perform (assuming of course that the mount has been properly polar aligned or set up). Since the shutter can be held open for several minutes, you can start to see stunning details develop on photos that would otherwise remain invisible with previously mentioned methods. For example, dust bands in galaxies and even color from otherwise dim dark gray objects come forth. And although I won't get into this, you can also get various filters, like H-alpha, to bring out details that wouldn't normally show up. When thinking of tracking mounts, most people envision an equatorial or alt-azimuth fork style that is driven by a motor. But there are a few manual tracking mounts out there such as the barn door tracker. Motorized tracking mounts aren't inexpensive (especially better quality ones that can support larger scopes), so for those who are happy using a long lens on their SLR to take some celestial shots, these are easy to make and, best of all, quite inexpensive.

Stay Sharp
Before ending this post I want to briefly discuss focusing. I talked a little about this in part "A" in regard to using the camera with a regular lens, but using a telescope can be a bit trickier. Speaking of tricks, there are a few that can be used to make things easier, but I'll start with some of the simple things first. Like astrophotography with a regular lens, aim for the moon. It's so far away that once you focus on it, stars, planets, etc., should all be in focus as well. Be warned though, your night vision might be temporarily compromised due to the brightness of earth's companion. If you're shooting using the prime-focus or eyepiece projection methods then of course the telescope's focuser will need to be adjusted, and if using the afocal setup, both the focuser and camera lens might need to be varied to get a sharp image. Planets and bright stars can also be aimed for in the moon's absence as they can generally be seen well enough.

By chance if you've already tried focusing on planets or stars, you might have noticed that it's still quite cumbersome to perform. The camera's LCD screen or viewfinder just doesn't give you as much luxury as using your own eyes directly with an eyepiece. But that's where some clever people came up with masks that you can temporarily attach to the front of your scope to aid with focusing. The cool part is that with a little effort these masks can be made with supplies as simple as a knife, cardboard and duct tape. Below are some links to these masks so you can read more about them:

Bahtinov mask
Carey mask
Hartmann mask / Scheiner disk

Keeping to the topic of nice sharp images, when shooting bright objects, strongly consider using your camera's mirror lock-up feature and if possible, use a remote to trigger the exposure. For example, if you just use your finger to press down on the shutter button, you'll likely notice that the telescope vibrates slightly for a few seconds; poorer quality mounts tend to be more prone to this, but even sturdier ones can exhibit some flex. Since the shutter speed for bright objects is quite fast, the resulting vibration form the button press may ruin the image. But by delaying the actual exposure for a few seconds this issue can easily be overcome. Now if you're using a point and shoot camera, or there is no mirror lock-up feature, not all is lost. In situations like this you can hold a matte black card in front of the lens, press the shutter button, wait a few seconds after the exposure is triggered, and then quickly move the card away from the lens; poor man's mirror lock-up. Remember to add a couple of extra seconds to the exposure time to compensate for this action.

Although I think I've broken a personal post size record, I've barely scratched the surface of astrophotography. In case you have a question or two, feel free to ask away and if I know the answer I'll be glad to help or point you in the right direction, likely in the form of a blog post. I definitely need a break from all this writing and I have yet to touch my paper airplane-a-day calendar, so I think I'll try my hand at that. L8r!

Web Resources

Telescope related: - Lots of articles here

Astrophotography related:

Astronomy magazines:
Amateur Astronomy
Astronomy Now
Sky and Telescope
The Astronomer

Telescope manufacturers:


General astronomy sites:
Astronomy Pic of the Day
Canadian Space Agency
European Space Agency
NASA Jet Propulsion Laboratory
Royal Astronomical Society of Canada
Science @ NASA
Institute for Space Imaging Science

Astronomy related software:
Sky View Cafe

Figure 1 - An old photo of my 10" Newtonian telescope on its Dobsonian (an alt-azimuth) mouth. A 28mm eyepiece is attached and you can also see the blue finderscope on top.

Figure 2 - Close-up view of the eyepiece holder and finderscope.

Figure 3 - A 1.25" 10mm Plossl eyepiece. Decent quality for viewing purposes.

Figure 4 - A 2" 28mm Plossl eyepiece. Excellent and bright wide-field viewing with this optic.

Figure 5 - This is my pride and joy, a high-end 1.25" 7mm eyepiece; almost 90 degree field of view, razor sharp and huge eye-relief which works well for photography and those who wear glasses. You can't quite tell from the photo, but this thing is huge; almost hard to wrap your hand around.

Figure 6 - Unlike cheap telescopes, higher quality ones require you to place an eyepiece adapter in them depending on the size of eyepiece you want to use. On the left is a 1.25" adapter and to its right is a 2" one.

Figure 7 - Here's a 1.25" variable Barlow lens. You put this into the telescope first, then the eyepiece goes into this unit, and the image is magnified by the value its set to. I've rarely used this one at 3X as the image becomes quite dark and somewhat soft.

Figure 8 - And here's my other Barlow lens, this one being a 2" model which magnifies the image 1.6X.

Figure 9 - Back almost a decade ago, I got this t-mount adapter so I could place my father's Contax camera (35mm film type) onto the telescope. This one didn't see much action and these days I use the Four Thirds one for my Olympus digital SLRs.

Figure 10 - This is an interesting 1.25" camera adapter (notice the threaded portion where the t-mount would screw onto) as you can either use it as an empty tube (prime focus) or place an eyepiece inside of it (afocal).

Figure 11 - This is also a camera adapter, but a 2" model.

Sunday, January 16, 2011

The Sky That Didn't Get Away

In the past few days, including most of today, I have been busily reviewing and editing some of my old digital photographs; some dating back seven or eight years. Only a couple of hours ago did I finally upload just over 100 photos, but I still have thousands of shots to go through, literally. If you check out my Flickr Photostream, you can peruse through these images. For interest, keep your eye on the camera I used for each pic; you'll see images from the now quite old Fujifilm FinePix 40i, the Sony DSC-S60 and the classic Olympus C5050Z.

But anyway, that's not the purpose of this post. Instead, it is about the image that you see below and I recommend you take a quick peek at the full size version; at least you can see some of the fainter stars. This photo brought back some fun memories for me. Succinctly, when I was attending university for my BSc in Computer Information Systems degree, I was told about a programming competition held at the University of Saskachewan and I decided to enter it along with a few other students. Since we were in Calgary, Alberta, this meant we all had a lengthy drive to Saskatoon. Although the scenery was a tad drab (it is the prairies after all) the drive was alright as the company was good.

Jumping ahead, we got to Saskatoon, checked into our cheap hotel, participated in the competition the next day, then had dinner and started the seven hour drive back to Calgary. During the trip to Saskatoon I rode with an instructor from the school and two fellow students, but a third student decided to take his own vehicle and drove alone. On the way back, I decided to keep him company and we chatted about various topics from the competition to daily life. Then a brief quite period manifested. I remember looking ahead, staring out at the headlight lit highway streaming at us and the nearby glow of the instructor's taillights ahead of us. It was just a little after eight in the evening, already completely dark, and we were somewhere close the border between Alberta and Saskatchewan. I got bored watching the yellow and white lines on the road entertain me, so I turned my head to look out the window next to me. This is where things got interesting.

Sounding quite excited, I asked the student to pull off to the side of the road. I told him that I just had to see the sky without a glass window in the way. He hunched closer to the steering wheel and peered up, and within a few moments flashed his headlights to let the lead car know we were stopping. Once we stopped I hopped out of the vehicle and by that time the folks in the car ahead where getting out also. They asked if anything was wrong and my driving buddy and I said, "nope but look up."

My eyes gazed up at the sky, quickly adapting to the darkness. For the first time in my life I saw the Milky Way. There were so many stars together in that galactic band that it actually did appear to softly glow. Unlike the long exposure photographs of our galaxy, I couldn't see its color, but still... it was awe inspiring to say the least. And because of our location, almost literally in the middle of nowhere, not a hint of light pollution spoiled the view as can be seen in the long exposure photograph below; that sky was an even pitch black. If only I had a dSLR and a wide-angle lens with me at the time (not to mention a tripod), I would've been able to capture this wonderful sight in much more detail. But alas, I had to make do with what I had. Since I couldn't handhold a 30 second exposure, I rested the camera on the student's vehicle by propping it up at an angle against the windshield wipers and managed to snap a few shots.

I wouldn't call this a great shot by any means, but it does remind me of something that was special to me. Considering a relatively inexpensive point and shoot camera developed this image, the color of a few bright stars can be seen a bit (plus a couple of hot pixels!) and evidence of how dark it was is clear. Oh well, at the least if I'm ever out in the middle of nowhere again, I'll be much better prepared. I've also been reminded by this that sometimes it's important to just take the shot if you can; don't let that moment get away --perfect picture or not.

Taken October 29, 2005 with the Sony DSC-S60 - 30 second exposure, 200 ISO, f/2.8 - Constellation of Cassiopeia visible middle left.

Thursday, January 13, 2011

Astrophotography, Part 1; Supplemental Post (A) - Photography with Imre - Episode 32

The world of astrophotography is not only an enormous topic, but a fascinating one too. Episode 32 of my photography series gave a very brief overview, but in this supplemental post I endeavor to provide much more detail. In future episodes relating to astrophotography, I'll be examining specific topics in more detail such as photographing auroras, planets and processing such images.

Shooting the Celestial Wonders Without a Telescope
I have a feeling that if you asked some people to describe astrophotography they would likely include the word "telescope" in their sentence. Yet, a telescope is by no means required to take some amazing photos of the night sky or even in daytime for solar photographers... here comes the warning.

Warning: Seriously said, viewing the Sun, whether with the naked eye, through a camera, telescope or some other means, can be very dangerous and can result in serious eye damage or even permanent blindness. Simply said, take extreme care when photographing the sun and ensure you've done your research and know what you're doing, otherwise don't do it. In almost all cases, special filters should be utilized on the camera lens or telescope (or other device) and ensure that you do not use filters that are attached to eyepieces. I don't believe these have been produced for many years due to safety issues, but they tended to crack as focused sunlight heated them up, which as far as I know led to some people getting eye injuries and even being blinded. Proper filters are generally attached securely to the end of the lens or telescope where the light enters.

For the rest of this post I'll be sticking to astrophotography during the night.

So like I said in the video, you can simply take your camera, attach a nice lens and start shooting. Well ok, it might not be that easy, but here are some things to keep in mind. First of all and as you have likely already discovered, shooting things in almost total darkness will not only require lengthy exposures, but something to keep your camera stable. I have to say, I'd be pretty impressed with anyone who could hold perfectly still while taking a fifteen minute long exposure to get some star trails. Thus, if you're keeping things fairly simple and do not require tracking (which I'll talk more about in the second part of this post), then whip out your tripod. Oh, and you'll also likely be shooting in manual mode, along with manually focusing, but I talk about that further down.

Next up is sensitivity, but what setting you should use may not be that straightforward. Many people would think that if conditions lack light then high sensitivity levels should be employed like 800, 1600 or even 3200 ISO. This of course means that the picture will be noisier than at lower lowers such as 100 or 200. Ok, fine, but how does this translate into what is needed for, let's say, some nice wide field shots? Well here's the trade off you'll need to consider:
  1. Using a low sensitivity setting will obviously reduce the noise that manifests on an image, but this of course also means that the sensor will not be as sensitive to light. So in a given exposure time, the sensor may not pick up some fainter stars/objects as it would at a higher setting.
  2. Using a high sensitivity setting will result in more noise being present, but in this case for a given exposure time the sensor will pick up fainter stars/objects than if at a lower setting.
So at this point you're probably getting the technical idea, but you might still be wondering which setting is better for certain types of shots like doing star trails, of the moon, or wide field shots with no star trails. Well, I think these three common scenarios deserve an explanation.
  • Star trails: In general, I would suggest trying lower sensitivity settings at first, even down to 100 ISO. In the end, the result will be a cleaner image and with a fast lens wide open you should still discover that a very large number of stars show up on the photo; in many cases more than you can see with the naked eye. In addition, if you are taking star trail type photos within a large town or city, light pollution will usually wash out the star trails much faster at high sensitivity levels. If possible, escape the confines of the city and perform such shooting in the peace, quiet and darkness of the countryside.
  • No star trails (e.g. constellations): Now we have another situation, and remember, in this case we only have a tripod; no tracking mount. In photos like this, we want to get nice little bright dots as seen in Figure 12, a photo I took of Orion (details under image). If the camera sensitivity is lower, then longer exposures will be needed to pick up all those lovely details and even the different colors stars give off. But as the earth rotates, the stars glide slowly across the sky as well as the frame, hence star trails. So we need to use a shorter exposure (due to lack of tracking mount) to limit the star trail effect. Therefore, in these types of shots increasing the sensitivity will help, even if it does introduce some noise into the equation; using a fast lens is also helpful to limit light loss.

    Speaking of lenses, there are two other very important factors to consider: focal length and where the lens is pointed to in the sky (thanks to a viewer for asking this excellent question which you can see in the video's comments). If you are shooting toward or at the celestial poles, then the length of exposure you can use will increase as stars don't move as quickly. However, if you're shooting toward or at the celestial equator, where stars are zipping across the sky more rapidly, then exposure times must be decreased because star trails will form faster. By the way, if you're not familiar with the idea of the celestial sphere, check out the Web resources section below. Moving on, this factor interacts with the focal length of the lens you're using. For example, with a fisheye lens (e.g. a diagonal type where one would get 180 degree field-of-view from corner to corner) you would get a very large swath of the sky and stars appear as very tiny dots. Because everything appears smaller, movement is not magnified as much, so you can get away with longer exposures than compared to using a telephoto lens with a greater focal length like 300mm or 600mm. But keep in mind, even pointing a wide angle lens toward the celestial equator will mean you'll have to reduce the exposure time if you don't want to see trails

    The viewer also asked how long the exposure times can be before trails appear. Unfortunately, I don't have any specific information in regard to this, but after a little poking around the Web I did find this post in a forum: The information seems valid enough, so this may act as a good starting point.
  • The moon: The moon is a fascinating subject, but in most wide angle lenses it looks like a bright white dot with little or no detail. But with a 150mm lens or larger you can take some very nice shots with detail showing on the lunar surface. Since the moon is fairly bright (although the brightness does change depending on the phase it's in), a moderate sensitivity setting is usually sufficient like around 200-400 ISO. You may have to play with the shutter speed to get just the right look, otherwise the moon may be blown out or underexposed, but don't be surprised if you're getting speeds around 1/250 of a second in some cases. Lastly, keep in mind that like stars, the moon too appears to travel across the sky due to the earth's rotation (in fact, the moon "moves" at a slightly different speed). By sticking to faster shutter speeds, you'll get a sharper image of our natural satellite.
Before moving on I just want to add that the above are just recommendations and with some practice and experimentation you may find that various other settings will provide you with the outcome you want, so as they say, have at it! In addition, for some shorter exposures a few of you may notice that the shot could be a tad sharper. Well that slight amount of blurriness could be caused by the mirror in the camera slapping up, thus creating vibrations that don't dissipate before the shutter opens. To help overcome this, and assuming you have the feature on your camera, use the mirror lock up function. This will slap the mirror up and out of the way when you are ready to take the picture, but the machine will let a few seconds pass (usually user customizable) before opening the shutter. Come to think of it, if you don't have a shutter release cable and must depress the shutter button by hand (how I do it), this can also allow for enough time to pass for the tripod to stop wobbling. For interest's sake, I have my camera set to two seconds.

Next up, I'd like to discuss the aperture of the lens and here are some of my thoughts about it. If my goal is to capture very faint stars/objects, then I generally use the widest aperture on my lens, which of course allows the most light through. On the other hand, although not usually very noticeable for some lenses, vignetting may occur (especially present when the sky isn't completely black) and often lenses are a bit sharper when closed down a little. So, if you aren't happy with how crisp the shot is, then try a smaller aperture. The evident downside to this is that less light will come through, so depending on the scene you're shooting, you may need to up the sensitivity or increase the exposure time if possible. As for the moon, you may find that stopping-down is fine, because as mentioned, the moon can be quite brilliant.

White balance should also be taken into account and I had a question about this on my earlier blog post. Most notably, you may have seen some wide-field photographs where the sky appears an odd orange tone instead of black. This color cast is caused by sodium type street lights and is prevalent in large towns and cities. But there are a couple of ways around this. First off is to simply travel to a location that is far from the light pollution; this generally means around a 30 minute to an hour drive away from the city. Another benefit of doing so, amongst others (like peace and quiet), is that you'll be able to capture and see much fainter stars and celestial objects than in the city. However, if travel is not possible, not all is lost. In my case, I almost always shoot RAW+JPEG and for such space based photos, I tend to exclusively use the RAW file. Although I could set the color temperature to something like tungsten, which will help cool off the image, for me, having the ability to set the temperature to wherever I want is a plus.

If you've already been involved with some astronomy, you've likely discovered how seeing conditions change due to many factors such as upper level winds, air temperature, dust/pollution levels in the atmosphere and moisture content in the air. Because these factors change from day to day, or even hour to hour, on some days the seeing conditions might be great and not as much of an orange cast shows itself on the image, while on other days the image looks less than desirable. So, this is basically why I like to take control. My advice to you here in regard to setting white balance, especially since one single color temperature generally won't work for all cases, is to experiment a little which will be a great way to see the results.

Great, we're getting there. You have your tripod up, camera securely attached, lens on and you've made up your mind about basic camera settings. Although a little tricky to see details in the camera's viewfinder, you manage to pick out a part of the sky to shoot and then press down on the shutter button only to discover that your camera doesn't want to take the shot. Why? Because it couldn't focus (ok, some cameras will take the shot depending on how they're set up and depending on the object you're shooting, but more often than not, focusing under such conditions can be an issue). Here are a couple of tips that should help. If the moon happens to be up in the night sky then use that to focus on. Even though it's much closer to us than even the nearest of stars, earth's satellite is at such a distance that this works well. There is a little downside though. Because of the moon's brightness, you may temporarily lose some of your night vision; just close your eyes for about 20-30 seconds after you're done focusing and your vision should recover.

Another thing you can do is to set your camera to focus on the center dot, aim at a really bright star, press the shutter button half-way, and once the camera is done focusing immediately switch to manual focus and do not touch the focusing ring. Most dSLRs are good enough to "see" that bright dot and lock onto it. Lastly, you may simply have to aim at a bright star like previously mentioned, but use manual focus and a few test shots to see if you got the focus right.

Holy smokes! I was going to write about using telescopes, but seeing how large this post is (and that I've been writing this for many, many hours over two days or so) I'll write a second part geared to that a little later (plus I'll have more resources to add). So happy shooting, be mindful of cold weather shooting if in such a climate and cya L8r!

Web Resources

Figure 1 - An old photo of my 10" Newtonian telescope on its Dobsonian (an alt-azimuth) mouth. A 28mm eyepiece is attached and you can also see the blue finderscope on top.

Figure 2 - Close-up view of the eyepiece holder and finderscope.

Figure 3 - A 1.25" 10mm Plossl eyepiece. Decent quality for viewing purposes.

Figure 4 - A 2" 28mm Plossl eyepiece. Excellent and bright wide-field viewing with this optic.

Figure 5 - This is my pride and joy, a high-end 1.25" 7mm eyepiece; almost 90 degree field of view, razor sharp and huge eye-relief which works well for photography and those who wear glasses. You can't quite tell from the photo, but this thing is huge; almost hard to wrap your hand around.

Figure 6 - Unlike cheap telescopes, higher quality ones require you to place an eyepiece adapter in them depending on the size of eyepiece you want to use. On the left is a 1.25" adapter and to its right is a 2" one.

Figure 7 - Here's a 1.25" variable Barlow lens. You put this into the telescope first, then the eyepiece goes into this unit, and the image is magnified by the value its set to. I've rarely used this one at 3X as the image becomes quite dark and somewhat soft.

Figure 8 - And here's my other Barlow lens, this one being a 2" model which magnifies the image 1.6X.

Figure 9 - Back almost a decade ago, I got this t-mount adapter so I could place my father's Contax camera (35mm film type) onto the telescope. This one didn't see much action and these days I use the Four Thirds one for my Olympus digital SLRs.

Figure 10 - This is an interesting 1.25" camera adapter (notice the threaded portion where the t-mount would screw onto) as you can either use it as an empty tube (prime focus) or place an eyepiece inside of it (afocal).

Figure 11 - This is also a camera adapter, but a 2" model.

Figure 12 - The constellation of Orion. Taken with the Olympus E-500, lens at 14mm (28mm in 35mm equivalent), f/3.5, 200 ISO, 30 sec. exposure

Tuesday, January 11, 2011

Astrophotography, Part 1 - Photography with Imre - Episode 32

After a few solid days of work, the introduction to astrophotography video is finally done!

I will have a lot more to write about in the supplemental post and to provide a little teaser I'll be including additional details in regard to telescopes, calculating magnification and other tidbits about astrophotography that I couldn't reasonably get into this episode.

Saturday, January 8, 2011

Can the foreground be blurred?

I thought I would take a quick moment and answer a question that was posted to my YouTube profile in regard to whether the foreground can be blurred when one is taking a photo. The answer is yes the foreground can be blurred and in fact is almost always blurry in almost every photograph taken.

This may not be very apparent in many cases though, because quite a few scenes do not have anything present in the foreground; more specifically, there is nothing to see between the subject (that is in focus) and the camera lens, except for mostly invisible air. In addition, if you're using auto-focus as many of us do, very commonly the camera system will focus on the thing nearest to the lens. This is of course assuming a general setting where multiple points throughout the frame are used to determine focus.

But there are a few different ways around this so you can get that blurred foreground and I'll present a couple of ideas here. To begin with, even if you're using auto-focus, switch to a single-point mode on your camera. This will allow you to either select the spot to focus on or you could just use the center point and the tactic of focusing on the subject you want crisp by putting the center dot on the subject, holding down the shutter button half-way, then framing the scene while still holding down the shutter button half-way and only pushing the button fully when ready. Personally, I most often use this method. In addition, you can also simply switch to manual focus, which more or less ensures you get focus on whatever you want.

However, composition must be part of the picture (excuse the pun!) as you still have to ensure that an object or two lies between the lens and the subject further in the distance. This is easier said than done as of course you pretty much have to get out there to scout locations and experiment with various angles which will end with the desired result. Nonetheless, it may be worth it and foreground objects, whether sharp or blurred, could add an interesting aspect to a photograph. Below I've posted a few of my shots in which a blurry foreground element is present.

Saturday, January 1, 2011

Some thoughts on full frame vs cropped sensor cameras. And Happy New Year!

First, I want to wish everyone a Happy and Prosperous New Year!

Second, I recently got an email from an individual who wants to purchase a dSLR, but asked for my thoughts on whether a full frame or cropped sensor type camera should be chosen --especially since this would be the person's first dSLR. I have to say that I thought this was an excellent question and it really had me considering both the technical and personal usage sides of this query; in fact, it was the latter that I hadn't really pondered in the past.

From a technical standpoint, full frame dSLRs generally have the upper hand over their cropped brethren primarily in regard to producing higher quality images (e.g. less noise at higher sensitivity settings) and shallower depth of field versus cropped sensors (great if you're doing portraitures). In addition, many full frame cameras have higher-end features like weather sealing, more durable build quality and shutter mechanisms, along with faster sequential shooting amongst other things.

As I continued to discuss the topic in my email, I couldn't help but include the old adage of the law of diminishing returns. Full frame cameras are almost always more expensive (sometimes substantially) than smaller sensor cams and frankly, it's not like cropped sensor machines don't deliver excellent results (think images from the Canon 5D/7D, Nikon D7000 or D300s, or even the E-5 from Olympus, including even some entry-level dSLRs). Full frame dSLRs are also generally large and weighty, including their lenses, so this might not be attractive to shooters who like to travel light. But here's where the line started to blur and some new branches sprouted.

What are your intentions with the camera? How are you going to use it? Are you just an enthusiast photog and will mostly record precious personal memories with the device with some artsy work thrown in? Are you planning to create large prints from your work and sell them? Or perhaps you want to become a professional photographer who does weddings or shooting for corporate clients?

Answering these questions, as well as others that may suit the scenario, will likely ease the decision that needs to be made. For interest's sake I've added some of my reasoning to a couple of situations, which might help you decide if you're ever faced with such a quandary.

If you're a hobbyist photographer, a full frame camera will likely be overkill, unless you have amassed some impressive personal wealth and spending upwards of five figures is pocket change so you really don't care. But otherwise, such a system will be quite expensive, many features will probably go unused and on the money saved buying a cropped type camera, one could invest into buying a few good lenses instead. Like I wrote in my email, I'd rather have a larger selection of lenses than a slightly better camera body with fewer pieces of glass. And if you plan to do some part-time shooting for money, say next to a day job like yours truly, even that may not justify getting a full frame beast assuming there are no special requirements (e.g. huge prints, like poster size or larger; plus see below). Even as a full-time photographer you may be able to employ a cropped sensor camera for things like weddings, portraitures and various other corporate work, and have little to no issues at all with such a camera type.

But what applications could a full frame camera be used for where you would really see it shine? Well, quite a few places actually. To begin with, most full framed machines have more pixels, thus work requiring larger prints will demonstrate their superiority in terms of resolution and cleaner images (less noise). Many can also shoot around eight to ten frames per second versus their lower-end buddies, so sports/action photographers will appreciate that. And many such photogs are also in environments where unpredictable weather could be an issue. Although not in all cases, most full frame models are sealed so they can handle higher levels of humidity, including being in rain or snowfall (but it's worth mentioning that there are several cropped sensor cams which are weather sealed too). Shooting in places where there's a lack of light or flash is prohibited for whatever reason makes full framers stand out. Since the sensors are quite large, the photosite (aka pixel) density is often lower, thus using higher sensitivity settings will usually result in images that are more usable compared to noisier cropped sensor sized cameras; serious astrophotographers might also see a benefit in this arena. Lastly, portrait photographers will achieve shallower depth of field more easily with such equipment, whereas cropped sensor users may need to find potentially more expensive fast lenses to get comparable results. I'm sure there are even more reasons, but I'm sure you get the idea.

Obviously there are far too many factors (personal, technical, financial, etc.) for me to go through, so it goes without saying that you'll ultimately be the one deciding on what to go with, if you're in such a position. Nonetheless, I found it quite interesting to consider such a proposition and mull over how I would handle this, and I certainly hope you find this useful.

Web Resources