DoF Calculating with Lens Distance Chart

[dwdallam]

First of all, the distance scale isn't that accurate, so measuring the distance with a tape measure and then dialing in the focus adjustment simply is not practical. You're much better off using AF with a single point where you want sharpest focus.

Second, if you're really going to be that anal about controlling DOF, you're going to need the tape measure and the DOF spreadsheet regardless. Measure your subject distance and input that (and your best estimate of focal length if using a zoom) into the sheet, and select aperture accordingly.
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That's what I've been doing, yes. I also think hitting the spot you want in focus, like you say, and then using your smallest aperture setting that renders enough detail is probably the best way. I say "best" because if you want X in focus and you want the background in focus too, and you spot focus on X and use your smallest aperture, then you either got it or you didn't, and it doesn't matter--your camera / lens is not capable of it.  And it's faster than all the calculating and measuring.

Thanks Jon.

[dwdallam]

Not to say some of the solutions proposed aren't viable, but wouldn't the easiest approach be to bang out a couple bracketed frames? Set up the shot and shoot f/8, f/11, f/16 then move on. You can pick which frame has the DOF you like best when you get home.

Messing with a calculator/chart/laser rangefinder seems a little bit of overkill, and perhaps more prone to error or miscalculation.
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What I said--yep.

[klane]

This statement is utterly wrong.
This statement is not wrong but meaningless in this context.

-- Olaf
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How is that utterly wrong?

please explain.

[01af]

DOF is focal length/distance dependent, not format size.[a href=\"index.php?act=findpost&pid=188047\"][{POST_SNAPBACK}][/a]

This statement is utterly wrong.[a href=\"index.php?act=findpost&pid=188170\"][{POST_SNAPBACK}][/a]

Longer the lens the more shallow your DOF becomes.[a href=\"index.php?act=findpost&pid=188047\"][{POST_SNAPBACK}][/a]

This statement is not wrong but meaningless in this context.[a href=\"index.php?act=findpost&pid=188170\"][{POST_SNAPBACK}][/a]

How is that utterly wrong?[a href=\"index.php?act=findpost&pid=189094\"][{POST_SNAPBACK}][/a]

1. DOF does depend on format size.

2. Whether DOF becomes wider, remains the same, or becomes shallower with a longer focal length depends on a wealth of other factors. So a blunt statement like yours, without providing context, is meaningless.

-- Olaf

[klane]

OK the second statement is a bit out of context, I see that.

But the first statement I feel as if we are talking about the same thing and wording it different.

Here is what im trying to say:

If we take two different to match a fov lets say FF 35mm sensor(5d) and MF sensor(A22)

We would need a 50mm for the 5d, we need a 70mm to match that on the A22

Shot at the same aperture and distance the 70mm on the A22 will produce a shallower dof.

I can understand what you are saying since by using a larger format we have to get closer to the subject to equal the same field of view, but my statement is correct as the 70mm is going give a thinner dof at the same distance and given aperture than the 50mm.  

I hope that makes more sense.

[01af]

If we take two different [focal lengths] to match a FOV, let's say 35-mm-format sensor (EOS 5D) and medium-format sensor (A22), we would need a 50 mm lens for the EOS 5D, we need a 70 mm to match that on the A22. Shot at the same aperture and distance, the 70 mm on the A22 will produce a shallower DOF.[a href=\"index.php?act=findpost&pid=189264\"][{POST_SNAPBACK}][/a]

That's right.

... my statement is correct as the 70 mm lens is going give a thinner DOF at the same distance and given aperture than the 50 mm. I hope that makes more sense.[a href=\"index.php?act=findpost&pid=189264\"][{POST_SNAPBACK}][/a]

Actually it makes no sense at all. Your statement was, DOF does not depend on format size. And that's definitely wrong. I cannot see how your example above is supposed to provide evidence for your erroneous statement.

-- Olaf

[Sheldon N]

Changing format size does affect DOF, and it affects it in the opposite direction that you think it would.

If you hold all things constant (focal length, aperture, focus distance, print size) and only change the size of the format, then the larger film format will have more depth of field than the smaller format. This is because the larger film format requires less enlargement to reach the desired print size, and therefore uses a less stringent COC.

It is only when you change focal lengths to match the FOV between formats that the larger format has less depth of field. The effect of lens focal length overpowers the effect of format size when calculating DOF.

A simple way to state it is:

Larger formats require the use of longer focal length lenses to accomplish any given photographic purpose, and that use of longer focal length lenses leads to functionally reduced depth of field.

[klane]

A simple way to state it is:

Larger formats require the use of longer focal length lenses to accomplish any given photographic purpose, and that use of longer focal length lenses leads to functionally reduced depth of field.
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Thats excactly what I was trying to say, thank you!