Chamonix 4x5- Creating a DOF Scale

[nimo956]

I just read Ken Rockwell's article on how to choose the sharpest aperture here:
http://www.kenrockwell.com/tech/focus.htm

Could someone tell me if I did this right:
1. I measured the circumference of the focus knob of my Chamonix 4x5 as 93mm.
2. A full revolution of the focus knob moves the front standard 20mm, giving a scale factor of 93/20 = 4.65
3. This yields the following roughly:

F/16- 3mm
F/22- 6mm
F/32- 12mm
F/45- 25mm
F/64- 51mm

4. I measured a piece of paper and made the markings at those distances. Then I attached it to my focus knob. It looks like this:

148904

Did I do everything correctly? Now I just need to figure out how to use this in the field exactly!

[Doremus Scudder]

Looks right to me. To use in the field, you must start at the "zero" mark at one focus extreme and then note the f-stop marking that is in that same position at the other focusing extreme. I don't know your camera, so I don't know if you're focusing closer or farther if you turn the knob that direction, if could be that "zero" should be the closest focus point or the farthest. The problem as I see it is that you need some way to accurately not the "zero position" at whatever point you focus on so you can read the appropriate f-stop at that position after you have focused on your second focus point. Eyeballing may be good enough, but you might need to install some indicators or make some marks...

FWIW, I use a similar system outlined on the LFinfo homepage here: http://www.largeformatphotography.info/fstop.html . All it entails is having a mm scale on the camera bed (or knob) and then consulting a table. I have the my table printed on a sticker that is stuck to my camera backs.

Best,

Doremus