I cannot be sure about our QuadTCC working with your scope to produce no reflections. However, i do know that our 130 field flattener will work and produce zero reflections. It has been designed with convex radii so that any light reflected from the filters will be dispersed toward the outside of the focal plane and not towards the middle.
here is a simple test that you can do to determine where the reflections originate. Take an image with your filters and no field flattener or telecompressor in the optical path. If you still see reflections, then it is caused by your filters. Filters like the Astrodon series, have a sharp cutoff of each color, so they will pass the principal color and reflect the ones outside their passband. The colors that are reflected back up toward the telecompressor will then be rejected if they are reflected back from the telecompressor down to the chip. They will not be able to pass thru the filter again. Other filters may have less steep cutoff, and thereby allow some of the reflected light to pass again thru the filter and produce halos or reflection artifacts.
I have used Astrodon filters in all of my cameras since many years now and have never seen reflections like the ones in your images. However, I know about your reflections because I did have multiple reflections from a set of less expensive filters.
As far as using our 130 Field Flattener, I can assure you that this will not produce reflections, even if your filters do not have a sharp cutoff. If you have been watching our group for some time, you may have seen images taken by Ignacio, a lot of them became APOD images, and you will see the contrast and zero reflections in all of his images. I worked with him years ago to produce just the right Flattener design geometry to eliminate even the slightest hint of reflections - Ignacio was extremely demanding that this optic works perfectly.
So, the solution might require both testing a different filter and a different field flattener. The problem is not coming from the main objective for sure. So try my suggestion of removing the field flattener first and see if the reflections go away. Then the solution might be either change the filters or change the field flattener or both for best results.
From: Jon <jonkelly999@...
Sent: Sat, Feb 13, 2021 6:08 am
Subject: [ap-ug] Reflections Nightmare - I'm ready to give up the hobby!
I have posted previously about reflections with a Riccardi reducer but now have the same issue with a native flattener and I have tried everything I can think off.
My objective is to purchase a QUADTCC to replace the Riccardi but I cant do this until I sort out the existing reflections which I now suspect are coming from the sensor/filters.
I have now spent over 20 imaging sessions since October trying to sort out the issue and it has become such a chore that I'm ready to give up the hobby - can anyone help?
Equipment - CFF 135/926mm, QHY600L, Chroma LRGB and 3nm Ha/OIII/SII.
I have tried reversing filters individually in all permutations, moved spacing from between Objective and Filters to between Filters and Sensor and its just balloon squeezing. One filter works, then another one doesn't. Lights work but flats don't or vice versa. Nothing I do seems to help.
I can take images with no bright stars ok but as soon as I try something like the Pleiades I have issues.
These are the latest test images on Pleiades, one for each filter - all 120s subs. All have reflections.
Can these reflections be resolved or am I wasting my time?
I would be very grateful if anyone could help or work with me to try and sort this out.