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Lozlo Sep 12, 2002 10:37 PM

Digital Camera's Depth of Field?
Below is something I read in the Nikon forum. Does anyone know if it's true? Is it really that limiting? Nikon brags about 'true depth of field' on their cameras...what's up with that?

"...CCD is so physically small on point and shoot camera’s, you’re depth of field pretty much looks like you only have the one aperture settings (permanently in F22..."


BillDrew Sep 12, 2002 11:31 PM

Not right at all. The depth of field is deaper than 35mm with consumer digicams because the lens has a much shorter focal length. A 50mm "equiv" lens in a consumer digicam has a physical focal length of something like 10mm. It is the short focal length that gives a deaper depth of field. It does vary with physical f/stop.

The same is true of all consumer digicams, though not to exactly the same degree for all.

Lozlo Sep 13, 2002 12:48 AM

Thanks for that answer, but I'm still curious...are you able to open the aperture wide and shoot with very little depth (blur the bg) as you can with a film camera?


BillDrew Sep 13, 2002 9:42 AM

Yes - if you are comparing it to a film camera with a 10mm lens. Which will only blur the background if it is *many* times as far away as the forground.

For portraits is not often possible to blur the background with using a consumer digicam. So the background blur is more often done with a photo editor instead.

[email protected] Sep 13, 2002 11:41 AM

Yes you can if the lighting condition alows you to select the widest aperature but the results may not meet your expectation. And I guess you're talking about taking portrait pictures, and for this purpose, you will use the telephoto position on your zoom lens, that's where the problem comes in, because at this position, the widest aperature will be much smaller, usually at F/4.5 to 5.6 or smaller, and the effects may not satify your needs. Most digicams have their widest aperature of F/2.8 at the wide angle position. So if you really want to use this application, you should consider to look at the SLR digicam with interchangable lenses options. Cheers

[Edited on 9-13-2002 by [email protected]]

padeye Sep 13, 2002 2:04 PM

The issue is not film vs. digital but the scaled down focal length as others have said. DOF calculation is very complex and I can direct you to some information but one of the biggest factors is magnification ratio. Think of it in terms of the ratio of the distance from film to lens nodal point compared to the nodal point to the subject.

If I shoot a portrait with an 85mm F2 lens on a 35mm camera I'll have shallow depth of field. If I shoot it with a 2/3 CCD camera I'll need a true focal length of about 21mm to get the same field of view at the same distance. Even though I'm seeing the same thing the magnification ratio is very different between the two cameras. Even if my lanes has an f2.0 aperture I cannot get the limited depth of field of the 35mm camera.

Nikon's "true depth of field" is a non-sequitur. It doesn't tell you anything but sounds like a feature to the uneducated. All cameras have a true depth of field. A pinhole camera may have a virtually infinite DOF and an 8x10 view camera at f5.6 may have an extremely shalllow one. Nikon's cameras are bound by the same rules of optics as everyone else.

bacellar Sep 13, 2002 2:13 PM

You should visit
where you find tables for calculating depth of field, unfortunately not available for short focal lenghs as in digicams but makes the subject clear, It's fun!

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