[pure-silver] Re: spacing new shutter
- From: "rob c" <spam@xxxxxxxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Sat, 18 Jun 2005 23:40:32 +0100
Sounds as though it may be possible to check for accuracy but adjusting for
accuracy may involve a lot of trial and error with shims unless a bench with
micrometer adjustment is available. Perhaps I will just change the shutter and
see how it is before deciding to send it away.
At 18/06/2005 13:06 -0700, you wrote:
>----- Original Message ----- From: "Spam" <spam@xxxxxxxxxxxxxxxxxxxx>
>To: <pure-silver@xxxxxxxxxxxxx>
>Sent: Saturday, June 18, 2005 9:02 AM
>Subject: [pure-silver] spacing new shutter
>
>
>>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. The schneider data sheets don't give a distance from flange to
>>flange of the front and rear lens, ie how thick the shutter should be. There
>>is some data of distance from front of front lens mount to rear of copal
>>shutter and rear of shutter to end of rear lens mount. This gives overall
>>length but doesn't cater for innacuracies of mount of lens elements within
>>the mount. I think this is why the spacers are important, because on an
>>optical bench they can be set to correct width for optimum of that particular
>>lens/shutter combination. In my neck of the woods optical benches are as
>>scarce as rocking horse poo!
>>
>>Is there a way to test this at home or does it mean sending lens away for
>>setting?
>>
>>rob champagne
> One way is to adjust for minimum oblique spherical. You need a very distant
> object. Focus so that this is sharp at the center of the field. Then move the
> image to the margin of the field and adjust the spacing for best sharpness
> there. You will have to juggle between center and edge a few times. The
> correct spacing is where you get the best compromise between sharpness at the
> two points.
> Some lenses are more sensitive to cell spacing than others. Tessars, for
> instance, are very sensitive, some symmetrical lenses much less so.
> I also agree with the idea that you should measure the spacing of the lens
> in the original shutter (assuming the image is good) and set the cells up in
> the new shutter for the same spacing. Unless you are changing the dimensions
> of the cells by machining them you can measure from the edges of the two cell
> rims.
>
>---
>Richard Knoppow
>Los Angeles, CA, USA
>dickburk@xxxxxxxxxxxxx
>
>
>
>---
>Richard Knoppow
>Los Angeles, CA, USA
>dickburk@xxxxxxxxxxxxx
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