View Full Version : Makro:Depth of Field calculations?
Well I just want to know what kind of Depth of Field I can get with a 4x5/5x7 ma kro 120mm lens; either Rodenstock or Schneider. Is there a sytem of calculation I can do to figure this out? If there isn`t, could you tell me what type of lens to use for a close up covering the aproximate dimensions 15 to 60cm wide by 30 to 70cm deep? This 3 dimentional space also has a height that ranges from 5 to 3 5cm. If at all possible I would like to keep most of these dimentions in focus. Is there some lens or leses that can pull it off? Cheers.
There are a number of on-line calculators, and formula are in a static page somewhere in photo.net. Any decent photo book will also have this information. See also some other posts over the last few days.
I'm not sure that I correctly understand your question. Say, your subject is 20x25cm. 4x5 film is about 10x12.5cm, so your magnigication is m=0.5. Conventional formulae for Depth of Field for a 120mm lens at f/45, CofC 0.1mm, give about 12.5cm (focus is from 30.8 to 43.3cm), and you seem to want 30cm. You get almost this much at f/90, if you can stop down that far.
For macro work, for a given magnification, changing the focal length has very little effect on the DofF. There are some very specialist techniques that might be usable, essentially by lighting a 'thin plane' of the subject, at the focused distance, and moving the subject down during a long exposure.
Before you ask, 35mm format would give you even less DofF.
My apologies for the statement about 35mm, it isn't correct, because we have small magnifications here. For 35mm format, magnification is m=0.144. For f=55mm, c=0.03, at f/45 (if you can get there), DoF = 20.5cm (which still isn't enough).
If anyone cares, and my apologies for going off topic, the 'cut-over' point where, for the same subject size and same aperture number, the DoF is equal in 35mm and 5x4 formats is about m=0.25 (35mm) and m=0.75 (5x4). The subject size is about 96mm by 144mm. For greater magnifications, 5x4 wins. For lesser magnifications, 35mm wins. This makes the usual assumptions inherent in the conventional DoF formulae.
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