[rollei_list] Re: OT: Repolish (question for Richard)

  • From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
  • To: <rollei_list@xxxxxxxxxxxxx>
  • Date: Fri, 11 Nov 2005 12:05:06 -0800


----- Original Message ----- From: "john" <raga@xxxxxxxx>
To: <rollei_list@xxxxxxxxxxxxx>
Sent: Thursday, November 10, 2005 11:35 PM
Subject: [rollei_list] OT: Repolish (question for Richard)


Does anyone have experience with polishing front elements with
extensive, contrast-reducing extremely fine "cleaning marks"? Did the
performance of the lens change?

The $195 it costs to have Focal Point do polish/coat/recollimate is
more than I can afford and out of proportion to the value of the
lens. A thread on kyphoto recommends an outfit in Tasmania (Longman
Optical) that will repolish a surface for $28, plus $14 to recoat. I
have a LTM Jupiter-3 (Russian Sonnar 1.5/50 clone). Might be worth
trying.It looks easy enough to extract the front element; I can
recollimate the lens myself (it's easy to get at and adjust the
shims). Perhaps leave it uncoated.

(I also have a collapsible LTM Summicron, but I don't feel competent
to try to collimate it if necessary--dunno how to get at the
shimming, if there is any...AFAIK Leitz matched the mount to the
specific focal length of the sample, and there are no shims).

Richard, do you know what kind of glass is used for the Sonnar front
element...is it "hard" and could be expected to stay unscratched
after polishing with normal care? (Probably so, the prewar Sonnars
were happily uncoated). If it were you, would you consider having
this procedure done?

John Wilton
www.ragarecords.com/photo

Repolishing a lens is not trivial. While element thickness is often the least critical of dimensions it is still important. To some degree element spacing can be used to compensate, that is probably what is meant by collimating.
I have several prescriptions for the Sonnar, I am not sure which one was used in production lenses. I will try to coreleate the glass specifications with the glass catalogue to figure what was used.
Its hard to know how much degradation of contrast comes from a few scratches. I have seen (and have) some lenses which have so many fine scratches that it acts like coarse ground glass, this definitely degrades the image but only a few scratches probably don't make enough difference to warrent the cost (and risk) of resurfacing the lens.
There is a lot of hand work involved so I think John van Stelten's prices are probably reasonable for what he offers. I would be suspicious of prices as cheap as the Tasmanian ones you quote.

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx

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