Friday, May 28, 2010

Part 2: Aperture Revisited - Photography with Imre - Episode 21

Now that's the way the episode on aperture should have been done the first time! I'm definitely happy with this show; properly scripted and plenty of diagrams and graphics to clearly illustrate the topic. Plus, I included a much better and detailed explanation of it too!

As usual, there are some links below if you'd like to find out a little more about the topic. Some of these sites (even Wiki, although I'm not a huge fan of it as more or less anyone can edit the articles) go into a fair bit of detail, but that of course that doesn't mean you need to know everything about f-numbers and entrance pupils to be a good photographer. As long as you have a strong grasp of the fundamentals, you'll be able to relate and manipulate settings with ease and most importantly, come away with the results you expected. And speaking of relating...

I did want to give a few more examples of how aperture, shutter speed, and sensitivity (ISO) interact. Below are some exposure settings that should result in virtually identical photos, except for depth of field which will change as the aperture size is manipulated:

1. Aperture: f/5.6  Shutter Speed: 1/15  ISO 200
2. Aperture: f/2.8  Shutter Speed: 1/60  ISO 200
3. Aperture: f/4     Shutter Speed: 1/15  ISO 100

I'll compare the second example to the first and third to the first as well to keep things simple. In the second example, the aperture size has been opened two full stops (from f/5.6 to f/4 to f/2.8), which means that four times as much light makes it through the lens (remember, if you open up one stop, twice as much light can get through). But to get the same result when taking the photo, the shutter speed is four times as fast; from 1/15th of a second to 1/60th of a second. Therefore, although four times as much light gets through to the sensor, the is only open for a quarter of the time.

As for the third example compared to the first, the aperture has been opened up one full stop, thus letting twice as much light through the lens. But you'll notice that the sensitivity of the sensor has been reduced to 100, which means that the sensor is now half as sensitive to light. And there you have it.

The last thing I'll quickly mention is in regard to depth of field. Although the size of the aperture affects how much of the photo will be in focus, distance to the subject (really to the point you're focusing) will also change the depth of field. As you may have already noticed, if you shoot a tiny little  insect with a macro lens set to f/4 let's say, only a millimeter or so of the picture is sharp. But point that same lens using the same f-stop at a mountain a kilometer away, and you'll likely see that pretty much everything is in focus!

So off I run for now! For the next episode, I'll be showing a neat trick shot that relates to aperture, so stay tuned for that! Also feel free to send me suggestions or questions for future episodes, and you never know, I just might honor your request! L8r!

Web Resources

http://en.wikipedia.org/wiki/F-number
http://en.wikipedia.org/wiki/Aperture
http://en.wikipedia.org/wiki/Entrance_pupil
http://www.dpreview.com/learn/?/Glossary/Exposure/Aperture_01.htm
http://digital-photography-school.com/aperture
http://www.photoxels.com/tutorial_aperture.html
http://www.cambridgeincolour.com/tutorials/camera-lenses.htm
http://blog.epicedits.com/2007/06/16/so-you-think-you-know-what-an-f-number-is/

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