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 Author Topic: DoF for 30D and 5D  (Read 2549 times)
Celeste Shuen
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 « on: March 08, 2006, 07:34:24 PM » Reply

The crop factor of 1.6 on 30D means that the Field of View (FoV) of a 5D is 1.6 times that of a 20D; so for a 5D to have the same FoV to a 20D set at 50mm, it will have to be set at 80mm.
My question is: suppose a 20D and a 5D are set at the same distance from the object and are adjusted to have the same FoV, what will the difference in the Depth of Fields (DoFs), if there is any,  between the two cameras be?
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DarkPenguin
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The 5D will have shallower DOF.  I can't remember how much.   Just over 1 stop, I think.
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Ray
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The 5D will have shallower DOF.  I can't remember how much.   Just over 1 stop, I think.
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That is correct, I believe, unless BJL is wrong   ) . I have to confess I've never actually tested this because the situation is complicated by the different performance of different lenses at different f/stops, as well as the different resolving capabilities of different format sensors.

I understand that theoretically, if one had a 12mp camera like the 20D with pixel quality equal to the 5D's, and if one had a 50mm lens which at f5 performed as well as the 80/1.8 (for example) at f8, then the DoF multiplier would be 1.6.

But these theoretical ideals rarely exist, so it's all approximation.

Sorry! It's not the 80/1.8 but the 85/1.8, so there's another complication.
 « Last Edit: March 08, 2006, 10:03:37 PM by Ray » Logged
benInMA
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There are depth of field calculators all over the web.

The difference is generally not that large when you're look at it with a calculator, but differences in the appearance of out of focus areas, etc.. seem to change more, and differences due to the different lenses used also exaggerate the visual difference.

e.x. for normal lenses

35mm film - 50mm - f/2.8 - 8ft - 1.3ft in focus
APS - 31mm - f/2.8 - 8ft - 2.93ft in focus     (lens chosen as allowing most similar FoV & working distance)

Sigma has a 31, when I was using my 10D they didn't have it yet, so you ended up with a 28mm or 35mm lens for your normal.

APS - 28mm - f/2.8 - 8ft - 3.65ft in focus

But what the calculator doesn't mention is how out of focus a given object is X distance out of the depth of field.

That's where the differences in visual appearance come from IMO.

edit: #s are slightly off because a 10D/20D/30D is not exactly the same size as APS film.
 « Last Edit: March 09, 2006, 08:43:52 AM by benInMA » Logged
jimhuber
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