Where to measure Depth of Field Large Format

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So for an small format camera at far enough distance you can probably take the film plane and lens to be the same distance from the subject

For large format though and especially at close up ( e.g 1m with 480 bellow for 240mm lens) where you measure the subject makes a considerable differance

So do we measure subject to camera distance at the film plane for DOF calculations?
 
acrobatic_Citron said:
So for an small format camera at far enough distance you can probably take the film plane and lens to be the same distance from the subject

For large format though and especially at close up ( e.g 1m with 480 bellow for 240mm lens) where you measure the subject makes a considerable differance

So do we measure subject to camera distance at the film plane for DOF calculations?
Click to expand...
This also affects MF cameras such as the Mamiya C220/330 type and this article is worth a look.
 
I haven't looked at the site Peter gave, so this is my provisional understanding.

Depth of field calculations depend on a number of variables, but two of them are the lens to film plane and lens to subject distances. In my day, these were named (algebraically) as u and v (or v and u...). For a thick lens (meaning anything other than a thin plastic one!) the point to measure the two distances from were the nodal planes of the lens, which typically would be at different physical locations on the lens - and never, as far as I know - marked. Most people would approximate to the centre, because it was never critically important.

In your case, I'd measure from the front of the lens since the depth of field is going to be very shallow and check on the ground glass stopped down. You can always use a narrow beam torch at the subject position to check sharpness if the light is insufficient.

You can (if you know the magnification) calculate back from that, but I'd rather not take that route of explanation...
 
acrobatic_Citron said:
So for an small format camera at far enough distance you can probably take the film plane and lens to be the same distance from the subject

For large format though and especially at close up ( e.g 1m with 480 bellow for 240mm lens) where you measure the subject makes a considerable differance

So do we measure subject to camera distance at the film plane for DOF calculations?
Click to expand...
I would measure it from the centre of the lens, ie around he plane of the shutter. This is unlikely to be precisely the correct position, but close enough, given how rough and ready any depth of field calculations will be in practice.
 
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