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01/16/2007 09:04:44 PM · #1 |
Why do digital lenses behave differntly to film camera lenses - eg When I went to look for a 50mm prime lens the guy in the shop said, in passing, that it behaved like an old fashioned 80mm lens.
If this is too complicated to explain here I'd appreciate a link to a good site, (or a recomendation for a good book), dealing with the more mathematical aspects of photography - I can find plenty of tutorials on CS2 etc on the web but I'm using Wikipedia for the more detailed stuff, such as calculation of f/stop diameters and sometimes I'd like a reliable alternative resource. |
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01/16/2007 09:07:20 PM · #2 |
The guy in the store was telling you what the equivalent field of view is.
Since the sensor on your camera has a 1.6x crop factor, the view through a 50mm lens on your camera has the same field of view as an 80mm lens on a film or full frame camera. |
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01/16/2007 09:10:36 PM · #3 |
| Thanks for that amazingly quick response. If it's not too much trouble, what's a crop factor ? I can figure out the obvious - my camera sensor crops the image, giving a narrower field of view, is this because of some limitation in the size of sensors compared to film sizes. Do all digital cameras do this ? Do they all have the same crop factor ? Does it make any difference ? |
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01/16/2007 09:13:38 PM · #4 |
You've got it right. The sensor covers less space than the regular film plane. That is what the crop factor is.
Not all DSLRs have the same crop factor though most of the Canons that aren't full frame are 1.6. I believe one of the 1D line has a 1.3 crop factor.
Nikon I believe is 1.5 and the Olympus is 2.0.
Message edited by author 2007-01-16 21:14:08. |
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01/16/2007 09:14:16 PM · #5 |
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01/16/2007 09:18:55 PM · #6 |
Originally posted by thelobster:
Why do digital lenses behave differntly to film camera lenses - eg When I went to look for a 50mm prime lens the guy in the shop said, in passing, that it behaved like an old fashioned 80mm lens.
If this is too complicated to explain here I'd appreciate a link to a good site, (or a recomendation for a good book), dealing with the more mathematical aspects of photography - I can find plenty of tutorials on CS2 etc on the web but I'm using Wikipedia for the more detailed stuff, such as calculation of f/stop diameters and sometimes I'd like a reliable alternative resource. |
In Layman's terms... I hope:
Best way to demonstrate is look at a 35mm negative and an APS negative. The APS negative is smaller. That's what is in your camera.
In the digital world, what you are doing is cutting the picture (crop factor). So basically that 50mm isn't seeing the whole world to your digital camera, it is only seeing what reaches the sensor which is APS sized not full 35mm size. This of course does not include "full frame" SLRs.
Now as far as a 50mm acting like a 80mm... Suppose you have an 4x6 print . We'll call this "Full Frame". Pretend the picture was taken using a 50mm lens. Now crop the picture off so that it is 1.5 times it's original size. (APS size). Use a color copier and make it an 4x6 again. What do you have, a 4x6 that appears closer to the subject than the orignal 4x6. So it almost looks like you took a step or two forward, so your 50mm "seems" like an 80mm.
Now in reality the lens didn't change so your real focal length is the same as a 50mm. What does this mean... means depth of field functions exactly the same as a 50mm and not an 80mm. Wide do people get all upset, mostly because of the wide angle. You need increasing wider lenses to have the camera "see" what the same lens would see on a full frame camera. You really never here telephoto shooters complain.
Hope that helps. |
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