Like the title says; how much depth of field is there in an enlarging lens? Is there a way to know? Do shorter focal length enlarging lenses have more depth of field, like a wider angle lens on a camera?
Does everyone know about this, except me? !!
thx!
An enlargin lens has as much depth of field as any other lens.
Depth of field is defined by two parameters, aperture and magnification (it’s really only aperture but magnification makes it easier to understand
in the real world).
Any lens of any focal length has exactly the same depth of field at the same aperture and magnification.
.
The reason we think wide angle lenses has greater depth of field is because we usually take photos of lower magnification with them. Would you actually walk up close and shoot with greater magnification depth of field is the same as a tele lens shooting from the distance, given the magnification is the same, ie the photographed focused object has the same size on the film.
it's physics so you have to abide
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There are formulas for computing DOF based on the focal length of the lens, the f-stop used, and the distance from the film to the subject. Search for COMPUTING DOF.
You can calculate the optimum aperture for enlarging warped negatives, or curved field lenses, based on the focus spread (based on view camera focus equation of Hansma).
N = 20/(1+M) * square root of 'dv'
N = Aperture number
20 = user dependent constant (circle of confusion 0.15mm for me)
M = magnification
'dv' = millimeters of focal depth on the enlarger column.
Yes the optimum focal point is, for all practical purposes, in the middle point of the 'dv' or focal spread. Just like focusing a view camera. The 'dv' is obtained by moving the whole head up and down and recording the distance between sharp and blurry.
Depth of field...now that's pretty straightforward. Dewpth of field, on the other hand...is a whole different kettle of fish!
Didn’t you mean depth of focus?Originally Posted by John Layton
Indeed. Depth of field is at the negative stage, depth of focus at the paper (image) plane.
I'm sure everyone understood what the OP was discussing. I am no expert, but with the distances involved and the flat-field nature of enlarging lenses, that whatever you want to call it, depth of field or focus, is pretty small (short?).
I was somewhat surprised when I tried some things (I guess because I didn’t do the math first - it was something else I was testing for). Basically I was raising and lowering the easel after focusing and found more slop could be tolerated than I had expected. Of course it depends on a number of things but anyway. Apologies for the pedantry.
Now you can laugh at the people that put a piece of paper under the focus loupe. I do, however, so I don't scratch the easel
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