PDA

View Full Version : Aperture Question Re 355 G-Claron

Robert McClure
5-Sep-2005, 14:19
I just found myself an f9 355 G-Claron. It has indicated f-stop markings down to f64. The lens can be stopped down to at least two more stops, to around what would be the equivalent of f128 (and then some).

Question: have the conservative German lens designers said, in effect, that beyond f64 they feel resolution suffers significantly enough (due to refraction) that they are not recommending exposing at smaller than f64?

What about for contact printing? (Yes, I know I'll probably just have to expose at those tinier apertures to find out!)

Thanks!!

sanking
5-Sep-2005, 14:37
Robert,

The term is diffraction, not refraction.

Diffraction-limited resolution depends on color of light, but can be roughly calculated by the formula Resolution = 1800/taking aperture. For example, if you make a negative at f/64 the diffraction-limited resolution is 1800/64, or 28 lppm. If the taking apertue is f/90, the diffraction limited resolutin is 20 lppm, at f/128 it is 14 lppm.

The limit of human vision is about 14 lppm at an optimum viewing distance of ten inches. If you don't view your prints any closer than ten inches you can probably get away with stopping down to f/128 if you contact print.

On the other hand, some people tend to view prints very critically from closer distance, and even with contact printing I can see a difference in apparent sharpness between f/64 and f/128, but not between f/64 and f/90.

John Boeckeler
5-Sep-2005, 16:16
My G Claron 355 is marked from f9 to f90. I bought it new about 8 years ago.

Robert McClure
6-Sep-2005, 09:58
Sandy, thanks for the terminology correction. The Resolution formula is also helpful!

John, the SN for my 355 puts it at 1996. Strange that the f90 designation and beyond would have been dropped. Since I am afflicted by CPD (Curious Photographer's Disorder) I will try to contact Schneider directly. Perhaps their deisre for "precision" (ha, ha!) will prompt them to answer a neophyte's questions!

Thanks!!

John Boeckeler
7-Sep-2005, 05:36
I'm a little curious too. My serial number is 14577542: according to the chart, made between April '95 and January '96.

Struan Gray
7-Sep-2005, 05:56
Some speculation.

First, the very small aperture settings (high f-numbers) on graphics arts lenses were not there for picture taking, but for when making half-tones with a ruled line screen. In this use the dots on the page are small replicas of the lens aperture, and small dots require small apertures.

Second, folklore has it that in the late stages of the G-claron's life cycle new ones were mostly being sold for use on regular cameras and not the repro-cameras they were originally designed for.

It would therefore make sense if Schneider stopped marking the very small stops on the aperture scales.

Another possibility: the lens was mounted in a shutter by someone other than the factory and they used or made an aperture scale that left off the smallest stops.

Robert McClure
7-Sep-2005, 06:32
John,

I will be sure to post on this thread any response from Schneider I receive. I emailed questions to their tech support address yesterday.

Struan,

Thanks! These are the first logical, plausible-sounding ideas I've received after having asked the question on at least one other occasion. I'll post Schneider responses.