[pure-silver] Re: spacing new shutter

  • From: Michael Briggs <MichaelBriggs@xxxxxxxxxxxxx>
  • To: pure-silver@xxxxxxxxxxxxx
  • Date: Sat, 18 Jun 2005 12:22:33 -0500 (CDT)

On 18-Jun-2005 Rob wrote:
> can anyone tell me if there is a very accurate way to adjust the spacing
> between the front elements and rear elements of a lens without using an
> optical bench.
> I have to replace a shutter and I want to make sure that the original spacing
> on the old shutter was correct.
> I can measure the old spacing and ensure the new spacing is the same but that
> does not tell me if the old spacing was accurate.
> The schneider lens has 2 spacing rings on the front element.  My guess is
> that the manufacturer uses the very thin spacing rings to compensate for
> manufacturing tolerances etc when they send out lenses with shutters
> included.

Is the lens currently in the original shutter, with the original shims?  Why do
you think want to check the original spacing in the old shutter?

If the lens has the original spacing, all that you have to do is duplicate the
current overall length when you move the lens cells to a different shutter. 
The specs on the thickness of Copal shutters are tight, +/- 0.025 mm according
to the instruction booklet for a Copal Press #1, so the new spacing should be
very close.  I don't know what the required spacing accuracy is to obtain
optimal performance, but suspect that it will be hard to measure performance
changes from 0.001 inch changes in the spacing.

If you think that the lens has been tampered with, probably the best course is
to send the lens to Schneider's repair service to be checked.

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