Optimal aperture for Rodenstock 210mm?

[Ken Grooms]

What is the optimal aperture for the Rodenstock 210mm f/5.6 Sironar-N MC?

How old is this lens (serial #10332xxx)? Thanks.

Ken

[Ken Grooms]

Thanks, Jim!

f/22-32

[Steve Hamley]

The optimal aperture you want is the one that gives you the depth of field you need.

Steve

[paulr]

In a lot of cases you'll have enough enough depth of field through a range of apertures. If everything you want in focus is in a single plane, you'll have enough d.o.f. at any aperture. Only one aperture will be sharpest on average from axis to edge. That's what the question's about.

With most modern lenses it's in the f16 to f22 range. Wider than that, it might be a bit sharper on axis, but you lose a lot of sharpness in the corners. Closed down much from that, overall sharpness declines from diffraction.

[Bob Salomon]

1981

[Brian K]

I do extensive lens testing and I find that most of the modern lenses are their sharpest in the f16 to f22 range. They can be extremely center sharp at f11 but will tend to lose the corners a bit and require very accurate focusing. When you start going past f22 you get more dof and more latitude in your focus, but the lens itself starts to lose sharpness due to diffraction. These are general statements and there are always exceptions, but as a general guide you'll find it most often true.

[Christopher Perez]

Occasionally wide open performance in the center of the field is also outstanding. I have seen this more with tessar formula lenses than plasmats. But I have a few plasmats that hold their own wide open, if you will.

[Brian Ellis]

Much of the time it's a matter of picking the aperture that gives you the depth of field you need while also providing maximum resolution. In other words, there may be a choice of apertures for the needed depth of field (e.g. anything smaller than f22) but only one that will combine needed depth of field with minimal loss of resolution. So except in a theoretical/optical bench sense it's hard to say that one aperture is the optimum, in practice it varies with the situation.

There are tables you can use to determine the optimum aperture in any given situation. Linhof published one that I use, another is included in Peterson and Hansma's articles in the March/April 1996 of Photo Techniques magazine. There is also an excellent article in this forum dealing with focusing the view camera that I think goes into all this. As a general proposition, the greater the distance between the near and far focus points the smaller the optimum aperture will be. But the question remains, "how small while also minimizing loss of resoltuion?" For that I think you need a table unless you want to do your own testing.