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Hypergraph6 aka Sharpstar150 - circular reflections

TS-Optics Hypergraph 6 Sh2-240 Troubleshooting Artifacts
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Georg N. Nyman avatar
Georg N. Nyman avatar
I would like to ask you about a problem, which I currently have under certain circumstances with the above mentioned OTA: Everything is fine as long as I do not use a full frame camera (I use QHY600M) with NB filters - if the target is very dim and of very low contrast - like currently the OIII emissions of SH2-240, I get on the stacked frames a circular reflection - see screenshot.
My optics train is - OTA with built-in corrector, Baader Universal filter system with 50x50mm square filters, QHY600M shooting the full frame. 
As you can imagine, as soon as I switch to my QHY268, no reflections anymore visible.
And even if I use my flats, those circular reflections do not vanish - meaning, that they even during taking the flats do exist - I observe the opposite effect - an overcompensation of the reflection - that area becomes darker than the other areas of the image. 
I have blackened all inside surfaces of the optical path after the corrector, but what is still unpainted is the outer rim of the deflection mirror - I was told, that all those telescopes are delivered with unpainted/unblackend sides of the deflection mirror - do you think that this might be the reason? 
What is your experience - have you had this as well and how did you get rid of it?
Thanks and CS
Georg
codwyer avatar
codwyer avatar
It look like the internal reflection if one of the dapaters, between the M63-M48 adapter that comes with the scope, and anythign else between there and the M54 attachment to the camera.
Hypergraph 6 does not like the imx455, its a torture test for most optics. I use the imx572 APS-C but also tried the full frame imx 410 and stopped using it with the hypergraph 6. APS-C is good, vignetting light fall off, but no issues with star shapes at the edges.

My guess is the bottleneck and reflection from an M48 sized attachment along the optical train, probably closer to the corrector and further from the sensor, i.e. the M63 to M48 adapter.

I use an M63 adapter for my APS-C on this scope, and instead screw it directly into the focuser housing above the corrector, so I keep the adapter aperture as wide as possible until I get to the sensor to avoid any vignetting or internal reflections.
Helpful
Brian Puhl avatar
Brian Puhl avatar
I had a very similar issue when I ran my newt at F/3 with the Nexus.      My solution was simply taking longer flats and bias exposures.    I made sure my flats were at least a second, and my bias were ~0.5 seconds or better.        Strange, but it fixed it for me.  Same exact issue.
Helpful Concise
Georg N. Nyman avatar
Georg N. Nyman avatar
Update: I have covered absulutely everything inside the OTA from the entry to the sensor with either a special black "velvet" or a superblack paint….. and tried it again with OIII - oh wonder!!! No reflections anymore! Job done!
Helpful Concise Engaging
Ashraf AbuSara avatar
Ashraf AbuSara avatar
Do you mind sharing what black paint you are using? I am having the same exact problem and I think I have to do the same.
Well Written Respectful
andrea tasselli avatar
andrea tasselli avatar
Just in case: MUSOU Black anti-reflective paint 100 ml - the world´s blackest black-TSBLACK100 (teleskop-express.de)
Ashraf AbuSara avatar
Ashraf AbuSara avatar
andrea tasselli:
Just in case: MUSOU Black anti-reflective paint 100 ml - the world´s blackest black-TSBLACK100 (teleskop-express.de)

Thank you. Wish focuser / scope makers would just spare us the trouble and make sure everything is painted with that color.
Georg N. Nyman avatar
Georg N. Nyman avatar
Ashraf AbuSara:
Do you mind sharing what black paint you are using? I am having the same exact problem and I think I have to do the same.

Yes....the one mentioned by Andrea - from TS
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