View Full Version : Review Request before submission: Making a dof calculator for your geared focus knob
Sean suggested me to compile a document for my recent answers to the Arca Brainb ox question. So I'm working on this document (http://www.phys.ufl.edu/~mhayashi/dofkno b.html) although the section for Example using Arca Swiss F-li ne Classic camera is not started yet; basically because I need to take pictures of my prototype and post them (I shouldn't have sold my Nikons when I started LF ...). Otherwise, 3/4 of the document is done and ready for submission to the LF homepage soon or later.
I was wondering if anyone is interested in reading, commenting, making a point f or correction or suggesting anything to the document before the submission. Than ks everyone. E-mail after May 17th should be directed to here (mailto:hayashi -@td5.so-net.ne.jp).
Sorry if you see "Contribute an answer" button in my document. It's not supposed to be there.
Is this some sort of arcane intellectual puzzle solving? Why not view the image on the ground glass at taking aperture (with a good loupe)? I bought my first 8x10 view years ago. At the time I had a ton of Nikon gear. When I realized that I was no longer shooting 35, and this took a while to set in, I went to KEH Camera Brokers (King had not been in business for a long time then) and sold all of my cameras, lenses, meters, all of it. Haven't looked back! IMHO anyone who wants to seriously learn photography should start out with 4 x 5 at a minimum! Sorry, I'm becoming a curmudgeon in my old age! WAES HAEIL! fred
no no Fred, I have never meant this document to be an intellectual puzzle solving. Or I don't even want to do that unless I get something worth to the effort and time I put in. I basically made a simple C-ring ring that calculates minimum f-number required for a given dof. "dof calculator" is rather misnomer in a sense (but of course f-number and dof are related). I had a reason (http://www.phys.ufl.edu/~mhayashi/dofknob.html#reason) to do this and it was worth it.
BTW, It's probably a good chance to buy something like Nikon Coolpix 950 or 990 for web purposes. I'm not a digi person yet so please be easy on this topic....
Good idea. This sounds similar to the DOF scale on the focussing knob of Rolleiflexes and other TLR type cameras.
Bob Salomon - HP Marketing
"Good idea. This sounds similar to the DOF scale on the focussing knob of Rolleiflexes and other TLR type cameras. "
The DOF scales like a Rollei one are for only one reproduction ratio. A view camera needs it for several.
Linhof uses a DOF calculator on their GTL called AMSthat computes DOF at several ratios and a different version on the M679 that computes 2 ratios.
The easiest, most convenient way for someone with any format camera from 35mm to 810 to compute DOF over several ratios is still the pocket sized Rodenstock circular calculator which also gives exposure increase as well as DOF for both level and inclined cameras and computes Scheimpflug movements as well.
By the time one is part way through entering all of the formulas the Rodenstock would have finished the calculations. And you don't need batter
Bob, thanks for your comment. As stated in the document, the dof calculator shows min. f-numbers at M=0 or infinity focus. However, the calculator essentially contains all the information at different magnifications as stated in Good things to know section:
The min. f-numbers calibrated are correct at magnification M = 0, infinity focus. However, at any magnification, the min. f-number required for a given delta will be less than that at infinity focus. Therefore you're always guaranteed to get min. dof for a given delta at any magnification.
At magnification M = 1 (life-size, 1:1), the min. f-numbers N on scale are half. At any magnification in between 0 and 1 (infinity focus), the min. f-number required will fall in between the f-number scales and their corresponding halves. For arbitrary N, use N(M) = 1/(1+M)*N(M=0) to figure out exact min. f-number required at M. For example, at M = 0.5, N(M=0.5) = 2/3*N(M=0). So multiply the f-numbers on scale by 2/3.
For example, if the scale is made for 4x5, the ring can be used for 8x10 as well by dividing a min. f-number by half, provided the circle of confusion for 4x5 is simply doubled. But one may want to have more than one ring for different formats to avoid confusion and mistakes.
I have the Rodenstock calculator. It's well made and I still use it if I want to calculate phi for accurate optimum plane of focus and if I have enough time. The Rodenstock is complete, having options for inclination angle (alpha), subject angle (beta), and min.f-numbers at different magnifications and formats. Most of the time, all my settings are alpha = 0, beta = 0, format size = 4x5, magnification = unknown (unless I'm doing macro). Then I bracket towards overexposure. I find the more options the calculator has, the more confusing and time consuming it can be. For example, I wasted my time guessing what beta should be until I figured out beta doesn't really matter unless I'm doing macro work. I also had to make sure format scale was on 4x5 and alpha was 0. My whole goal to make this calculator was not about completeness, but it was about moment.
I'm lucky because my Cambo Legend comes with a depth of field calculator built in. I called Calumet and was able to find out that the assumed circle of confusion is 0.30mm for the 8x10 scale and 0.15mm for the 4x5 scale.
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