View Full Version : How do I position this lens relative to film plane?

Robert Edward McClure
23-Jul-2007, 20:41
I am building a hand-held camera and want to affix one of my wide lenses, more or less, permanently. The "Hobo" is an example of the concept I am working with here.

I am confused. Do I just focus the lens at infinity, at, say, the smallest aperature. Then note hyperfocal point, and so on, for each aperature down to wide open?

Then I guess, because I will be working on a "rangefinder" basis, I would take a light reading, determine the longest shutter speed the scene can tolerate, set the corresponding aperature, then live with whatever hyperfocal distance this generates.

I think I understand, but I have become a little confused.

Thanks in Advance, Ladies and Gentlemen


C. D. Keth
23-Jul-2007, 21:06
I would do it with the hyperfocal of the widest aperture, personally. This would give you the closest distance you can have in focus and still limit your depth of field. Then, to get focus closer than that you just stop down.

Donald Qualls
24-Jul-2007, 15:10
Another option, if you don't mind a tiny bit of added complexity, would be to use a large format style lens board, set at infinity, and then use shims under the lens board to provide hyperfocal at, say, f/8, hyperfocal at f/16, and hyperfocal at the smallest aperture you reasonably expect to use (I use f/32 fairly regularly with my Speed Graphic, hand held, but I also routinely load ISO 400) -- you could even throw in one for a reasonable portrait distance (say around 4-6 feet), though that would get to be a pretty "thick" shim with anything like a normal lens. Depending on the lens, the "shims" might start to resemble an extended lens board, but you could "extend" the camera's front panel to keep the shims inside the body and not have to worry much about their light tightness -- that is, make the front panel with a well that will accept the lens board and shims; for infinity, you install the lens board and then put all the shims in front, for other focus settings you put different shims or combinations of shims behind the board and the remainder in front. Done this way, you'll be able to use the same slide lock or similar mount retainer for all setups.

At first glance this might seem to violate the simplicity of the Hobo concept, but in use, it would require only a few seconds to change focus settings, while still avoiding the need for ground glass, tripods, etc. and allowing rapid, hand-held photography with much more versatility than a fixed-focus camera with the limited DOF available even with very small apertures in large format.

Robert Edward McClure
24-Jul-2007, 16:28
Thanks, guys. This helps!

Glenn Thoreson
25-Jul-2007, 12:10
I recently built a fixed focus 4X5 box camera. I used an old 121mm WA lens, fucused for the hyperfocal distance at f/11. 34 feet, I believe. It will give closer focus as it's stopped down. That's not really important to me, as it will be used for landscapes. At f/11, the area of acceptable apparent sharpness would be a bit over 17 feet to infinity. That's good enough for what I will do with it. The first shot with it looked really good. Unfortunately, the negative got destroyed, so I can't show you.

Robert Edward McClure
25-Jul-2007, 12:42
Thanks, Glenn! Very helpful, also. (You do know, of course, "accidental destruction of a negative" is a sign of genius - sort of like Einstein, allegedly, failing fourth grade math - ha, ha!)