Optimum aperture for a G- Claron

[John Kasaian]

Somewhere I read on this forum that G-Clarons perform their best at f/32. I'm curious as to if this applies to both the newer G-Clarons and the older Dagor types, or just the Dagor types, or just the newer ones.

I have a Dagor type G-Claron and it performs beautifully at f/32, but as I was setting up this afternoon on Sonora Pass, it occurred to me that maybe I shouldn't be so cavalier about this f/32 "aperture priority" business, so I thought I'd better ask the experts here.

[David Rees]

I've learned not to use my G Claron 270mm f9 at f90 (it dates from the 70s, I believe). Happy to use it between f22 and f64. Haven't noticed significant difference between f22 and f32, at least on my lens.

[Joe Forks]

John,
What focal length and format are you shooting? I _believe_ the circle of illumination is much larger than the circle of sharp definition but usable coverage increases as you stop down further. So it would just depend on image circle and format as to how much you could afford to open up. I believe I read somewhere that either F16 or F22 will offer optimum sharpness, but F32 or smaller could be required if you are pushing the limits of your format.

I also believe that 270mm WA G claron is a different beast. I don't have personal experience with it but my understanding is that it has a large image circle but sharp definition falls off rather rapidly.

I should know better than to spout stuff I read on the net, but I suppose if I'm mistaken someone will be along shortly to refute my statements, so we'll see :)

Best
Joe

[John Kasaian]

I'm shooting an f/9 240mm on an 8x10.

The WA G-Clarons are a different lens entirely according to the Schneider Rep I corresponded with a few years back.

~Cheers!

[Joe Forks]

As you probably know Schneider rates the coverage at a conservative 64°at F22, but coverage at F45 is reported to be closer to 80°. If this is true then F22 barely covers or doesn't quite cover 8x10 and equals no movements. You are probably limited to F32 or F45 in most cases.

I own a Doctor 240mm F9 Germinar which is very similar 6/4 design, F9 and 70° coverage. Mr Thalmann says F22 covers 8x10 with modest movements. F32 or F45 will provide "significant movements with good corner to corner sharpness". I suspect your G Claron is very similar in that regard.

Forks

[Brian Ellis]

I don't know that G Clarons perform "best" at any particular aperture. However, the design of the lens is such that the usable image circle gets larger and larger as you stop down more and more. That's one of the reasons why these lenses cover so much more than their specs would indicate.

[Christopher Perez]

My 305 and the 240 GClarons I've used in the past all worked brilliantly from f/9 through f/32. Stopping down gets sharper edges at the extremes of field coverage. But that's about it.

[Gregory Gomez]

I have used a 210 f9 G-Claron on an 8x10 wide open with focus on infinity. The lens covers this format under these conditions with movements. I would judge the image circle with the lens wide open to be about 400mm. The image circle grows even wider when the lens is stopped down, and reaches its largest dimension at f22. The image circle grows larger still when the lens is focused on objects closer than infinity. At one-to-one reproduction, the image circle is very large.

I also have the 240 f9 G-Claron. Its image circle is bigger than the one created by the 210 model.

The optimum aperture for G-Clarons, according to Ron Wisner and Schneider, is f22. Ron believes that the G-Clarons are the closet lenses that one can buy today to Goerz Dagors.

All recent G-Clarons are single coated and have been optimized for one-to-one reproduction. When stopped down to f22, they perform very well at 1-to-10 to infinity.

I hope this helps.

[paulr]

I think the reason for recommending the small apertures is that these lenses are optimized for small magnification copy work. They're actually apo lenses at and around 1:1. if you use them at infinity, stopping down keeps the performance from degrading too much, especially off axis.

[Brian Ellis]

"The image circle grows even wider when the lens is stopped down, and reaches its largest dimension at f22."

With G Claron lenses the usable image circle or the circle of good definition continues to increase the farther down you go, AFAIK it doesn't stop increasing at f22. There was a long discussion about this aspect of the G Claron design on the Wisner bulletin board some years ago.