My MPC 90mm super macro lens

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Lou Jost
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Post by Lou Jost »

That was discussed extensively in the linked thread, where Rik made an excellent argument, by considering the limiting cases. If the baffle is right at the sensor, it does nothing! Likewise if it is right at the aperture. The effectiveness of the baffle increases as you move away from either extreme. Somewhere near the middle (the exact spot is difficult to know) is the best balance.

MarkSturtevant
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Post by MarkSturtevant »

Perhaps it is to stop the light rays before they can reflect off of something, rather than blocking them afterwards.
Mark Sturtevant
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ChrisR
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Post by ChrisR »

I've got an old pic for that too :)

Image

Unfortunately it can be difficult to mount baffles "in the middle", so wherever you can, would be better than nothing.

Also too as well, not all the reflections off the sides of the tubes will be "mirror", some will be diffuse, so I'd guess the more baffles the better.
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Post by rjlittlefield »

MarkSturtevant wrote:Perhaps it is to stop the light rays before they can reflect off of something, rather than blocking them afterwards.
ChrisR wrote:I'd guess the more baffles the better.
Both are true, at least up to a point. The goal is to prevent indirect paths from any point on the aperture to any point on the sensor, via reflections from the sides of bellows or tubes or whatever. Diffuse reflectors are harder to handle than mirror reflectors, because the diffuse reflector will send light all over the place after the reflection, producing a lot more paths to block.

I have seen highly detailed technical papers on optimal baffle design for telescopes, but "optimal" in that case was something like using minimal material given that you could put the baffles anywhere. With rigs like we use there are usually lots of other constraints, so optimal becomes something like getting the best baffle shape at each of those few positions where a baffle can be placed at all.

--Rik

MarkSturtevant
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Post by MarkSturtevant »

I have meanwhile managed to expand the flocking with Protostar, and I put in a mock-up of a rectangular baffle sort of near the sensor. This was done before the recent bit of discussion. It is certainly true that it is hard to put up a baffle near the middle; at least I could not figure one in my case.

So here I show a longish tube of double-layered flocking material mounted near the front of the Pixco tube. It extends to pretty near the rear when the tube is fully retracted. The oily and reflective insides that are exposed when the tube is extended will be in much deeper shadow.
Image
Image

The mock-up rectangular baffle is shown next. It is mounted between the Pixco tube and the rear part of the Neewer ring, so it is a bit over 20mm away from the entrance to the camera. Not too close to the sensor, I hope. It is at present made of black paper. I can make a much better one once I get a feel for what size is good and avoids vignetting. Right now the rectangle matches the size of the camera sensor (~ 22mm X 15mm).
Image

Can't really test the modifications now since the camera body is in the shop, getting its sensor cleaned. But I am excited about these additions! Very useful and profitable discussion for me here!
I am also ready to build a 2nd super macro out of other parts. This will be smaller but about as powerful. Its best feature is that it will zoom in and out a lot faster and easier because it will be built around a de-glassed telextender (that idea is very much inspired by Johan J Ingles-Le Nobel). Slow zoom is an issue with the Pixco tube since it takes many, many turns to change its length.
Mark Sturtevant
Dept. of Still Waters

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