Choice for the Circle of Confusion?

[Drew Wiley]

Whhhhat, Neil? I know what you're implying regarding circle of confusion; but some of us might like our prints worthy of viewing both up close and at a distance. I'm stating this for sake of argument, and not just in relation to the poster's special requirements or your response to it. But it is how I actually approach the issue. I simply don't believe in any of that "normal viewing distance" nonsense. Do we need to place a gold nylon rope around our framed work, along with a security guard, to keep people at a prescribed distance? You stated things as if, the bigger the print is, the less sharp we need to make it, which of course would be a misrepresentation of what you probably meant; but it still came across that way.

[Doremus Scudder]

I approach the CoC issue from another perspective. The goal when making negatives is to find the optimum compromise between depth-of-field and diffraction, i.e., finding the aperture that gets the job done while providing the most possibility for enlargement. Scenes with a very shallow depth-of-field end up allowing for a great deal of enlargement, but often a scene will require a very small aperture to get everything acceptably sharp, thereby limiting the degree to which it can be enlarged. I made tables years ago, using a rather small CoC, which show the maximum acceptable (for me) print size for the aperture used. This has served me well over the years.

FWIW, f/32 for 4x5 work makes stunning 11x14-inch prints and enlarges well to 16x20. Even the occasional 20x24 print works if the viewing distance is not too close. The proof is really in the enlargement itself.

Best,

Doremus

[Drew Wiley]

As formats get bigger and lenses longer, and as images get enlarged to greater sizes, depth of field issues require more and more strategic thought. There are numerous factors and options. But a blanket approach or formula might prove counterproductive, both in a mechanical and esthetic sense. With long-lens 8x10 work particularly, which I tend to enlarge, I find that it is important to prioritize what parts of the scene need to be in acute focus, and which are subsidiary, in a support role, so to speak. I'd generally rather do that than just throw a blanket over the whole thing in terms of theoretical diffraction limits, increasingly confusing circles of confusion, and so forth. Contact printers might logically approach the problem from a different angle. But when I contact print, it's apt to be with the same negs that I enlarge, and intend to be versatile.

[neil poulsen]

. . . I made tables years ago, using a rather small CoC, which show the maximum acceptable (for me) print size for the aperture used. This has served me well over the years. . . .

Thanks Doremus! . . . Of course, that's the "obvious" solution. (Not so obvious to me, I guess.) As it is, I will have tables for each of three formats. I couldn't see, in addition, having tables for multiple prints sizes. It also helps that, I tend to print small.

I appreciate everyone's input. This has been quite a productive thread.

[Tin Can]

Bob,

I have an original NOS Rodenstock DOF Calculator in hand, with case and 2 pages of fine print instructions. In German and English.

I am studying!

Thank you Alan!

And Bob Salomon

It is now called the Linos calculator as Rodenstock Precision Optical was sold to Linos and then Linos was sold to Qioptiq.

The scale is about the width of a dress shirt pocket as the calculator easily fits in one, in its case. One side calculates DOF at several scales for 35mm to 810. So it can also calculate DOF for DSLR FF Cameras. It also calculates the angle of the camera to the subject.

The opposite side calculates Scheimpflug for the same film sizes and also camera angles.
Lastly the calculator will indicate how much exposure correction might be required, depending on the chosen image scale.

The scales are printed in very legible type on the calculators and are easily readable even with my 78 year old eyes with or without my glasses.

While it comes with a detailed instruction sheet the designer, Dr, Schön, numbered each step to do the calculation determination and even his some pictograms to show what each step is doing on the calculator.

Unlike dragging a DSLR out with you to do the DOF the Linos weighs about 2 or 3 ozs and fits flat in your shirt pocket. In all the years that we distributed them we never had one wear out nor had we ever had to replace one. They are extremely durable and easily cleaned off, if necessary. Rodenstock also supplied them OEM for other European companies like Sinar and Linhof without reports of problems, save for people who didn’t read the instruction sheet. But simple, short telephone conversations fixed those problems.

[Bob Salomon]

Bob,

I have an original NOS Rodenstock DOF Calculator in hand, with case and 2 pages of fine print instructions. In German and English.

I am studying!

Thank you Alan!

And Bob Salomon

Enjoy!