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Old Jan 18, 2005, 4:55 PM   #1
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Traditional 35mm cameras have aperture ranges like f/2 to f/22.
Digital cameras seem to have smaller ranges, like f/3 to f/6.

How come? Does this really mean I can't get the depth of
field I would get with a 35mm film camera at f/22?

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Old Jan 18, 2005, 5:05 PM   #2
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You must be talking about digital point & shoots. The F-stop range on DSLR's is the same as on film based slr's. Depending on the lens F1.2 to F32 is possible.

With the tiny lenses in P&S (remember that in P&S the real lens range starts around 5mm) it is a matter of physics. If the diaphragm opening becomes too small, you stop getting good images and start getting all kinds of diffraction problems.

With these P&S cameras you get ahuge depth of field even withthe largest aperturesof F2.8 because the actual lens in them would fallin the ultra-wide-angle range for SLR's.The P&S cameras are actually shallowDOF challenged.:lol:It is really hard to get a background to blur out in many images.

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Old Jan 18, 2005, 5:12 PM   #3
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pbaxter wrote:
Quote:
Traditional 35mm cameras have aperture ranges like f/2 to f/22.
Digital cameras seem to have smaller ranges, like f/3 to f/6.

How come? Does this really mean I can't get the depth of
field I would get with a 35mm film camera at f/22?

Non-DSLR Digital Cameras have very small sensors. As a result, you have a much greater 35mm equivalent focal length, for any given actual focal length.

Some of these models have sensors so small that shooting at f/2.8 has almost as much depth of field as f/22 on a 35mm model.

This isa great thing if you want more depth of field (more of a scene in focus). But, it's a bad thing if you are trying to blur backgrounds by using a larger aperture (smaller f/stop number) to help your subject stand out from distracting backgrounds.

See this handy Depth of Field Calculator to see how this works. If you select a camera model, and plug in the actual focal length of a lens (you'll see a table containing this information for many models), coupled with a focus distance and aperture, you'll see why it's extremely difficult to get a shallow depth of field with a non-DSLR model.

http://www.dofmaster.com/dofjs.html




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Old Jan 18, 2005, 5:43 PM   #4
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Aperture is relative to focal length. So f2.0 on a 100mm lens is quite a bit bigger than f2.0 on a 28mm lens. Digital cameras may claim to have such and such 'equivalent' focal lengths but their REAL focal lengths are much smaller.

For example, the actual focal length of the Sony V3 zoom lens is 7mm - 28mm and the aperture range is f2.8 - f8.0 (in 1/3 stops). At 7mm and f8.0, the physical size of the aperture on the V3 is less than 1mm across which is small enough to cause a diffraction effect across the entire image...making it softer. As you open up the aperture (or increase the zoom) the size of the opening gets large enough that the diffraction effect disappears.

If digital cameras could stop down to f22, the opening would be so small that it might be difficult for the camera to get enough light to the sensor AND the diffraction effect would be much more pronounced. It would be unusable.
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Old Jan 19, 2005, 9:16 AM   #5
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Thank you all for your answers.
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