Is depth of field for landscapes dependent upon hyperfocal distance only? Then, is what you see in the ground glass exactly the final product, or, like with smaller cameras, is some of the depth of field "hidden" from view?

-- Jon Paul (jonspaul@jps.net), September 28, 1999

Answers

DOF is a lot more maaleable than you think. It basically hinges on the circles of confusion. When you focus, only one plane is theoretically in focus and light from this plane is focussed (theoretically) to a point at the film plane. Objects in front of and behind this plane form a small circle at the film plane which is referred to as a circle of confusion. Obviously the circles of confusion get progressively larger the more they are in front or behind the plane of sharp focus. The notion of DOF comes from the fact that if this circle is reasonably small, it doesn't matter and the eye will perceive it as a point. Try enlarging a picture a great deal and comparing it to a much smaller version - you should see smaller DOF on the larger picture than on the smaller picture. That's because the circles of confusion were enlarged sufficiently for the eye to notice that they were no longer points i.e., they are recognized as being out of focus. Whether you are able to judge DOF on the ground glass is iffy - it depends on your eyesight, teh amount of enlargement you're planning and the amount of enlargement the loupe you're using provides. Hyperfocal distances are based on assumptions about circles of confusion which themselves are based on assumptions about how much enlarging will be done. In general, they provide a nice enough safety margin to make them very usable in practical terms. These aspects are absolutely the same across formats (DOF across formats, of course varies as a function of longer lenses although that is qualified by the fact that you are enlarging less and you can stop down more with larger formats, which means more of a loss of speed - scheimpflug can help too). Hope this helps. DJ

-- N Dhananjay (ndhanu@umich.edu), September 28, 1999.

Your depth of field on the groundglass is exactly what the film would see, IF THE LENS IS STOPPED DOWN. When you are focusing wide open then the depth of field is minimized and what you see at f8 is not what you will get at f64. So stopping the lens down to the taking aperture, waiting long enough for your eyes to get used to the dim, dark groundglass will reveal what the film will see.

I should point out that you can see every bit of depth of field on a 35 mm camera if once again, you stop down the lens. Unfortunately this is feature that has been dropped by many 35 mm camera manufacturers.

-- David Grandy (dgrandy@accesscable.net), September 28, 1999.

"I should point out that you can see every bit of depth of field on a 35 mm camera if once again, you stop down the lens. Unfortunately this is feature that has been dropped by many 35 mm camera manufacturers. "

Not really. You only see the finder of 35mm camera with very low magnification. This would be the depth of field for a print of that same magnification or less.

With a view camera, stopped down to the required aperture, you can use a 4x, 6x, 8x, 10x loupe and see what the DOF is at that magnification.

Although unlike a 35mm finder, not all at once.

Also you can only see the limited DOF on 35mm if you use an SLR. Some of us use rangefinder 35s and then you don't see any DOF.

-- Bob Salomon (bobsalomon@mindspring.com), September 28, 1999.

Depth of field is a complex subject and to understand it you need a working knowledge of physics and maths. If, like me, you're a dumbo the best answer is to get a really good depth of field chart. You can download an excellent chart from Willis Boyce at www.gestalt- nassau.com/wbb. It is in the form of an Excel spreadsheet and you can set any focal length of lens, any circle of confusion and any subject distance. By the way, don't confuse the apparent increase in d.o.f. obtainable by using your swings and tilts with the real thing... depth of field remains the same, it's the PLANE of focus which changes! Regards,

-- Garry Edwards (creativephoto@hotmail.com), December 02, 1999.