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07-24-2011, 01:29 PM   #1
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Lens - Reflection absorbing tube function

I recently had the good fortune to but a 200mm/f4 Takumar SMC lens in very nice condition. Unfortunately, when it arrived the rear, flanged, tube which has the function of absorbing stray reflections, fell out the back. (The 135mm f3.5 lens also has an equivalent piece.) I could see three dabs of glue residue, indicating this part had originally been glued in place, presumably with a glue that could be easily broken, for service work. I eventually decidied to glue the tube back in using the grade of Loctite intended to stop screw threads working loose.

This was good fortune because I obtained pictures showing what the tube does

The images attached are:
1. Before repair, bright overcast day at Pebble Beach CA.
2. Before repair, dull light in Carmel Forest CA.
3. After repair, looking direct into a bright light. The green crescent effect can be observed with the light in a variety of positions near the edge of the image (note DSLR cropping) but not with the light near the centre of the image - features in the middle of the image are not 'artistic'.
4. After repair, looking almost direct into sun on a wet day, Mawson Lakes, South Australia.
5. After repair, bright day, normal scene, Mawson Lakes.

The stray light reflections result in fogging the middle of the image.

Overall I am pleased with the lens, but it is long enough on DSLR that I have not yet had much chance to use it.

Interesting knowledge for me, as an engiener.

Attached Images

Last edited by tim60; 07-24-2011 at 01:35 PM. Reason: corrections and improving information
07-28-2011, 07:10 AM   #2
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there have been several threads about internal reflections and similar symptoms in the photos.

I have a Rikenon 135F2.8 which had a shinny black rear lens group ounting ring that caused similar problems and another forum member had a 645-K mount adaptor which was shinny and reflective that did the same thing.

just goes to show how important internal reflection is
07-29-2011, 12:09 AM   #3
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Lowell, thanks for responding. I had not found the other threads. I did think it intersting to show the effect on images of this component, and I have learned something about the lens through this experience that I would not have learned had it been in correct order when it arrived.

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