Toho focusing question

[Peter Esbensen]

For those of you with a Toho FC-45X or similar camera, how do you determine the appropriate F stop? On my previous camera, a Toyo 45CF, there was a scale that I could use to determine how far apart the near and far points were for my desired depth of focus. Then I'd look up that distance (in millimeters) on a cheat sheet to figure out what F stop to use.

I don't see any such scale on my Toho. I also don't see any obvious place to paste a homemade scale onto the camera. So how do people figure this out?

Thanks for any help you might have!

[Ralph Barker]

How about taping a cloth measuring tape, like those used in sewing, to the front standard? You could then conveniently measure the distance to the rear standard at both focus points to determine the difference for use with your cheat sheet.

[Jim Rice]

I do it via the groundglass image. I focus and tilt/swing wide open, and then stop down for the elements in between. I like the range of f 22~32, though I'm sure I get some diffraction in there.

[Alan Davenport]

You could add a scale to your camera. It looks like you could fit a mm scale somewhere on the monorail. Or, find find a landmark on the front and rear, measure at both focus points, take the difference.

[Scott Schroeder]

I made dial on the focusing knob that leonard describes here:
http://www.math.nwu.edu/~len/photos/pages/dof_essay.pdf (http://www.math.nwu.edu/~len/photos/pages/dof_essay.pdf)
Using the technique outlined here
http://www.largeformatphotography.info/fstop.html (http://www.largeformatphotography.info/fstop.html)
you can focus far and near and using the dial see what the spread is and apply the proper f stop.

[Leonard Evens]

You just tape a scale to the rail. I bought an adhesive backed metal tape with a metric side. I have enough left over for a hundred view cameras. I would be happy to mail you an appropriate tape segment if you send me your address.

You do have to remove the Toho logo on the side to which you affix the scale. It is just held on with adhesive and comes off easily.

Scott already referred you to my essay at

www.math.northwestern.edu/~len/photos/pages/dof_essay.pdf

That lets me estimate distances to a few tenths of a mm. What I did was to photograph a metric scale with a digital camera, scale it appropriately in a photoeditor, print it out and affix it to the focusing knob. Since the focusing knob is geared down with respect to the rail, movement on the knob magnifies movement along the rail allowing for more precise measurements. (You can also make do with a handmade scale of the same sort.)

As Scott indicated, there are a couple of simple methods for determining f-stop from focus spread. One is simply to multiply the focus spread by ten and divide the result by two. A fussier standard is obtained by using Paul Hansma's method described at the reference Scott gave you.

[J. Wolfe]

I carry a tailor's tape in my pocket and measure the extensions from the lensboard to the film plane. Then I have tables in my notebook for each lens.

[Peter Esbensen]

Thanks to all for all the great suggestions!