hyper-focal distance for 90mm on 8x10

greenspun.com : LUSENET : Large format photography : One Thread

I was hoping someone can help me with this calculation. I am building a box to mount a 90mm superangulon, to shoot 8x10 film. (I know it won't cover; that doesn't bother me). Found on Schneider website tables which show hyperfocal distance for 4x5 and 5x7, but not 8x10 (because lens doesn't cover format). For 4x5 it was about 10', and for 5x7 about 8.5', so I'm guessing about 7'-8' should provide adequate focus from a few feet to infinity. Measured with my 4x5 the film to lensboard distance focussed at 8' (about 115 mm). Just thought I'd see if anyone else has done something like this, and can tell me the depth of box they built. Thanks for any assistance. Sharon

-- Sharon Gervasoni (lightmonke@aol.com), December 10, 2001

I would build the box to put the focus at about 50-100 feet and then use insertable matboard shims behind the lensboard to focus the lens closer based on your review of test pictures with various shims inserted.

I say this because I found with the Hobo that the recommended hyperfocal settings were quite unacceptable: the first thing viewers do when scrutinizing an 8x10 chrome is move in very close to see how sharp those things are off in the distance.

It's very difficult to build a box camera precisely anyway--a millimeter can make a huge difference--so some sort of shim arrangement is advisable in any case; once you have the option of inserting and removing shims you may find that you sometimes set the focus closer (for street photography involving people) and sometimes further (for grand-vista types of landscapes).

I discussed my thinking about the importance of infinity focus awhile back on the MF Digest forum:

http://www.photo.net/bboard/q-and-a-fetch-msg?msg_id=001QGu

But whether you agree with those opinions or not, incorporating some sort of shim arrangement will let you shoot a set of transparencies so you can tailor your camera to your particular lens, holders, and focusing preferences.

Feel free to e-mail me if you have comments/questions/criticisms....

<

-- Micah (micahmarty@aol.com), December 10, 2001.

Assuming that you are happy with Schneider's choice of Circle of Confusion for 4x5 and are willing to just scale it up proportionately for 8x10, then the hyperfocal distance will just be half that given for 4x5. You don't mention aperture, though - you do realise that the HF depends on aperture, don't you?

-- Huw Evans (hgjevans@yahoo.co.uk), December 10, 2001.

Sharon, The calculator at the below site will be useful.

http://www.frii.com/~mbaltuch/HyperFocal.html

-- Linas Kudzma (lkudzma@compuserve.com), December 11, 2001.

Yes, Huw--I realized after I posted that I forgot to include that I intend to maximize dof at F22-F32. Thanks for the responses so far!

-- Sharon Gervasoni (lightmonke@aol.com), December 11, 2001.

Try this on-line calculator:

http://albedo.net/~marko/main/dof.htm

It gives the following hyperfocal distances for 8x10 (I rounded them off):

f/8 - 11 f/11 - 8 ft f/16 - 5 1/2 ft f/22 - 4 ft f/32 - 2 3/4 ft f/45 - 2 ft

I can't vouch for its accuracy.

Don Wallace

-- Don Wallace (don.wallace@nlc-bnc.ca), December 11, 2001.

On-line calculators!? Good grief! Has everyone gone berserk?

The equation for hyperfocal distance is simply:

h = f*f/(c*N)

where f is the focal length of the lens, N is the f-number, and c is the diameter of the circle of confusion (CoC). Use the same units, e.g., millimeters for f, c, and h. If you get the answer, h, in mm, divide by 304.8 to get feet.

The only thing to argue about here is the choice of c. Marko's calculator above uses 0.3mm for 8x10, although I think that 0.2mm is a more common choice (and 0.1mm for 4x5, 0.025 for 35mm, etc.).

I'll try not to start my rant about why you'd go to a larger format and then allow a larger CoC.

-- John H. Henderson (jhende03@harris.com), December 12, 2001.

I should have said, "The calculator on Marko's web site," instead of "Marko's calculator." Marko credits Michael Gillett with writing the calculator.

-- John H. Henderson (jhende03@harris.com), December 12, 2001.