Depth of Field Question

[Pro-Vista]

I've just got a 1Ds MkIII attached to a Canon 24-105mm IS f/4 lens (i.e. the latest kit). I bought this lens for studio work, where I'm almost always shooting at f/8 @ 1/125. Previously, I used a Nikon fit Kodak DCS SLR with a 24-70mm Nikon lens (f/2.8), shooting at the same aperture and speed.

However, I'm noticing that the depth of field (I think this is the issue, rather than wrong focussing) seems a lot, lot narrower, so any subjects further back fall quite quickly out of focus.

Am I doing something wrong, or does this lens/setup have a narrower DoF compared to my old Nikon kit? I hope not, bearing in mind how much I've forked out for it!!

Thanks.
Pro-Vista

[jeffcable]

Originally Posted by Pro-Vista

Am I doing something wrong, or does this lens/setup have a narrower DoF compared to my old Nikon kit?

Thanks.
Pro-Vista

The DCS/n was a 14Mpx body and it used a full frame sensor (35mm equivalent) if I am not mistaken. The Canon uses an APS-h sized sensor giving you a 1.3x field of crop. Lens focal length has an effect on depth of field and the longer the focal length the less depth of field will be available, at any given aperture.

Your 24 ~105mm lens is 35mm longer, at the 105mm end, than the 70mm of the 24~70mm lens which you used to use. If your habit is to turn the zoom ring to longest focal length, then your Canon lens will have less available absolute depth of field at 105mm (albeit somewhat negated by the smaller sensor size) than the 70mm of the the Nikon lens.

OTOH, you are shooting in a studio, and you can use a smaller aperture to regain your lost depth of field. Often, studio shooting can require that one has minimal depth of field settings so there is one possible advantage to your current lens.

Personally speaking, a lens with a maximum aperture of f/4.0 is going to be a bit too slow to produce knife-edge thin differential focus and it requires something like the 85mm f/1.2, which would most certainly be the puppy for that type of work. YMMV

[Jerry Skrocki]

It's actually the other way around. The Nikon branded Kodak DSC 760 is a 6 megapixel 1.3 cropped ccd sensor and the Canon EOS 1Ds Mark III is a full frame 21.1 megapixel cmos sensor camera.

The full frame camera will exhibit a greater depth of field range (fewer objects in focus) while the crop frame sensor will have a smaller range (more objects in focus).

[Pro-Vista]

Hi guys,

Sorry to have mislead you. My Kodak was a full frame Pro SLR/n, and my Canon is, of course full frame. Therefore, I don't think it's anything to do with this.

Any other suggestions????

[Jerry Skrocki]

Originally Posted by Pro-Vista

Hi guys,

Sorry to have mislead you. My Kodak was a full frame Pro SLR/n, and my Canon is, of course full frame. Therefore, I don't think it's anything to do with this.

Any other suggestions????

You are comparing 2 different lenses from 2 different manufacturers. One lens is Canon f/4 with a longer telephoto range (24-105 IS) and the other Nikon f/2.8 with a shorter telephoto range (24-70). Did you shoot at the same focal length with each lens as well? I think the focal distance has a lot to do with the difference you are seeing.

[Pro-Vista]

I haven't checked the focal distance in detail, but I know from the type of shots I've taken with the new Canon lens that the problem certainly occurs at the wider angle end of each zoom lens, not the telephoto end. In other words, at that range of the lens where DoF should be greater. I'm really confused/concerned!!

Just another thought. I'm using the full AF function (rather than manual). Could this be anything to do with it? (I can't think why this could be, as my problem is that although to closest subject is in focus, the furthest isn't.)

[jeffcable]

Originally Posted by Pro-Vista

I haven't checked the focal distance in detail, but I know from the type of shots I've taken with the new Canon lens that the problem certainly occurs at the wider angle end of each zoom lens, not the telephoto end. In other words, at that range of the lens where DoF should be greater. I'm really confused/concerned!!

Just another thought. I'm using the full AF function (rather than manual). Could this be anything to do with it? (I can't think why this could be, as my problem is that although to closest subject is in focus, the furthest isn't.)

I had taken it that you had meant the full frame DCS but I had misread the Canon as the 1D3 rather than the 1Ds3. My apologies to you for the confusion. As to your issue... 24mm on full frame gives a 24mm angle of view approximating to about an 84 degree angle of view. I cannot see how the depth of field should be different at the same focal length. (I am not saying it isn't possible, just that I don't see how it would be the case... YMMV)

EDIT:
Canon Lenses :: Angle of View // sweeting.org

The interactive chart shows the focal length of various lenses on the Kodak to be within a negligible number of minutes of the angle of view on the Canon 1Ds. Not all lenses are there and it appears not to be comparing really up to date cameras or lenses but instructive, nevertheless.

I now wonder if the lens is not focussing accurately and as it is possible to get a poor copy, it is probably worth your while to take it into a Canon service centre and have them check and calibrate it.

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