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I have been trying to get  a Riccardi M82 0.75 reducer to play nicely with my CFF 135mm refractor, Full Frame CMOS camera and Chroma 50mm filters for several months and have adjusted spacing down to what seems to be optimum, finally using 0.10mm  steps.  This graph shows convergence of center and corner focus at 77.94mm spacing which is not far off the theoretical value when the 3mm thick filters are taken into account.


I can get almost round stars in the corners with some wavelengths(filters) but others are disappointingly elongated.

The main issue however is reflections in Lum, Blue and OIII, the Blue and Lum can be seen here.


I have also used the CFF/RR and no filters with a D750 and this also showed reflections so I don't think its the filters that are the problem.

I have been able to somewhat reduce reflections by reversing the orientation of individual filters but they are still present in Lum and Blue - I haven't tried reversing the OIII filter yet but that may help. I have also noticed the Riccardi is slightly soft in one corner - seen on two different cameras and this doesn't seem to be tilt related. I have seen varying amounts of tilt with each spacing I tried but with the current spacing tilt is very low at 2 or 3 percent (CCDI).

I have a dedicated flattener for the CFF and whilst I only briefly tested it with the Nikon D750 it all looked very good and I didn't see any reflection in the brief testing I did. I will do some more detailed testing with this and the CMOS when the clouds clear.

I know someone who has an almost identical set up but with an older Riccardi and they don't get reflections, so whilst I don't know for sure where the issue is arising I am suspecting the Riccardi.

I'm pretty much out of ideas and starting to consider a replacement for the Riccardi but there don't seem to be many suitable reducers and also no guarantees that something else would be any better - any suggestions?




Edited by Midnight_lightning
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  • 1 month later...

Sorry to see you didn't get much of a response to your problem! I can't offer any clues either, but would like to ask if you have been able to sort out the reflections? I'm considering the CFF as well and the question of suitable reducers is an important one.

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