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View Full Version : how to read a depth of field table?

8-Sep-2009, 20:22
Hi, Was just wondering what the figures meant on a depth of field table? For example, when looking at Schneiders depth of field table on their website, on the 8 x 10 format at a focus distance of 10 feet, shooting at 5.6, they give the near measurement as
9.63 (ft) and the far measurement as 10.28 (ft). Just wondering what they mean? By looking at these tables, I also came to the conclusion that by shooting at f2.8 on a 150mm lens on the 5 x 4 format, I would be achieving the same drop in focus as the aforementioned on 8 x 10. Basically I am looking to shoot full body portraits, wide open at 2.8, to get a shallow drop of depth, that would basically emulate this... From the sample images I am going off, the photographer has the image sharp from their eyes to their ears and then the image (background) falls off sharply.. Does the distance between the near and far measurements on a depth of field table, mean I should have sharpness from those distances? As mentioned before, I am looking to get both eyes and ears sharp... Or is the best way just to stop down? With my earlier tests shooting this wide open, I had trouble getting the person sharp. Also, was just wondering what an acceptable shutter speed (slowest) is to be using when using a field camera on a tripod?

Ok, thanks so much, any info and all of your thoughts would be greatly appreciated!!

Best Regards Josh

Nathan Potter
9-Sep-2009, 07:53
The Schneider table means just what it says - the near limit at 9.63 ft. and the far limit at 10.28 ft. with the point of best focus (PoF) at 10 ft. What the defocus is, (Circle of Confusion) at the near and far points is not specified but is often taken to be 100 um (5 Line Pairs per mm.) for Large Format lenses. The 100um CoC diameter can be taken to be about what can be resolved by the average human eye at a reading distance of say 12 to 16 inches. So that is suitable for an 8X10 contact print that would produce a just resolvable detail within the near and far focus points at f/5.6.

Nate Potter, Austin TX.

reellis67
9-Sep-2009, 09:35
Does the distance between the near and far measurements on a depth of field table, mean I should have sharpness from those distances?

A very simple way to approach this is to consider that the area between these distances will appear sharp, while the areas before and after these distances will not.

Or is the best way just to stop down?

I would suggest that the best way would be to look at the ground glass with a loupe. A large format camera is the ultimate what-you-see-is-what-you-get tool. The loupe will allow you to judge the results prior to exposure so you can stop down as needed to get exactly what you want.

As far as shutter speed goes, the tripod allows any exposure to work well so long as your subject does not move ;)

- Randy

Frank R
9-Sep-2009, 09:42
These help:

http://www.dofmaster.com/dofjs.html

http://www.cambridgeincolour.com/tutorials/hyperfocal-distance.htm

Peter De Smidt
9-Sep-2009, 10:45
Do test before exposing critical shots. Depth-of-field tables make some assumptions regarding enlargement size and allow circle-of-confusion sizes. (A circle-of-confusion is the effect that when out-of -ocus a point gets inflated to a disk. The bigger the circle, the less point-like a point would be.) For example, most depth of field scales on lenses assume a very small print. When I use my Nikon an Fuji depth of field scales, I stop down two stops from what is indicated as needed. I might be wrong, but the Schneider and Sinar scales also seem to be based on a small enlargement size. So, get a friendly test subject and take some pictures at various f-stops to see what you like best. An f2.8 150mm lens on a 4x5 would have a razor thin depth of field. Lenses that fast for 4x5, such as an Aero-Ektar, are rare. It'll be hard for the model to keep still enough that what you want to be in focus will be in focus when you click the shutter.

Leonard Evens
9-Sep-2009, 13:31
As Peter and others have said, the depth of field figures given in a table are based on assumptions. But the tables are also calculated on the assumption that the lens is perfect. In reality, lens aberrations will decrease DOF, particularly as you move from the center of the field. Also, few large format lenses are meant to be used wide open where the aberrations may be fairly large. In particular, because of curvature of filed, you may be misled about exactly what is in sharp focus. So Peter's advice to make some tests is very much to the point.