Sironar S lens SHIMS - lens experts help needed

[paul_4875]

I am fitting my Littman with a 135mm sironar S, but when I unscrewed the front element from the copal 0 shutter, I find a small shim set between the lens and shutter, really thin - perhaps a fraction of a mm - obviously put there by Rodenstock, as its a brand new lens.

However, the Littman requires that the front element is removed often to close the camera. I will loose this shim at some point if I have to do this, so I wondered: can I put it on the rear element unit, thus maintaining the lens' rear-of-front-section to front-of-back-section distance, or is it affecting something else?

perhaps someone can also explain the purpose of such a shim, although how to get around it is more important than the theory for now..

[Vamsi M]

Hi,

This is a question which can only be answered authoritatively by an optical engineer. Perhaps the company rep. can put you in touch with one.

I have read (I think on usenet) that the shims are critical to maintain the performance of the lens. The precise placement of the stop can affect the performance of a lens, so I would not mess with it. It may well be that the loss of sharpness won't be noticed in many situations, especially in a handheld camera. However, in my opinion, if you've spent the extra money on a Sironar-S for it's technical performance, it doesn't make sense to degrade that characteristic.

Vamsi

[Frank Petronio]

Why are you wasting a Sironar-S on a Littmann? It's not like you need the coverage. I would trade you an shim-less N plus $$$ for the S....

[paul_4875]

a sironar S is not just about coverage Frank - it's able to shoot a stop faster (i.e. a stop wider open)
which is rather important in a hand held camera.

[James E Galvin]

The spacing between the elements is much more critical than the stop placement, so moving the shim to the back should OK.

[Ole Tjugen]

If it's a stop faster you need, I'll trade you a Schneider Xenar Series 1C 150/3.5 for it - it cost me all of $40...

[paul_4875]

thanks Jim, that's what I suspected, but needed an expert like you to confirm.

interestingly enough - the mounting threads inside the otherwise identical Copal 0 shutters are different - so... I need to swap the shutter unit as well as the lens element units, which is annoying, as its a tight squeeze in this camera.

(it has an apo symmar 150 in Copal 0 at present)

[paul_4875]

"If it's a stop faster you need, I'll trade you a Schneider Xenar Series 1C 150/3.5 for it - it cost me all of $40..."

what is this - a street vendors market?? largeformatbarter.com??

I need ultimate resolution at a wider than normal aperture.
there's only one modern multi coated lens that specifically does that - the Sironar S.

[Ole Tjugen]

I just couldn't help myself...

But form my experience, the difference between older singlecoated and modern multicoated lenses in terms of sharpness, resolution and contrast is overrated. Will the resolution still be "ultimate" when the shim has been moved - or even removed?

I also have a (single-coated) Planar 135/3.5 which will have to be pried from my cold, dead hands.

[Michael Jones]

Praying I do not get flamed for this suggestion: email Bob Soloman at HP for the answer.

bob at hpmarketingcorp dot com

Good luck.

Mike