Of late, I have been having a lot more reflections in my images than I reckon I should have. This shot was really a quick effort to see what happened. It consists of 5x660sec at 800iso on my tak 130F with flattener, attached to a modded 40D cooled DSLR. I have taken HH before and not had this result, yeah I have had some small reflection around the bright star, but nothing remotely like this. As I said a very quick and nasty with only flats and bias applied, no darks. I have been told to expect some reflection around bright stars with my refractor, but I feel this is over the top. Any suggestions etc welcome
That's a very sweet shot You could get rid of that halo easily in PS by using a difference layer as a mask. There are a few tuts around. Alnitak always casts this kinf of artefacts. I don't think it's a limitation of your gear. This is an extreme case really. Like the pleiades.
Pete, you actually have 2 reflections in this image. All I can sugest is getting a good antireflective UV/IR filter and mounting it at the end of the imaging train and see if a reduction in reflection is possible. I have had quite some improvement using a Baader IR blocking filter mounted on the end of the camera adapter. Not a total resolution, but not a failure either. The QHY8 has reflections from the CCD to the filter or reducer in front on any bright stars and this has reduced significantly.
Stuart, have been using the flattener for over 12 months, it has never caused this sort of artifact(I am referring to the large reflection at present). I did notice that the eos clip LPAS filter was a tad loose in its mounting, maybe this could be the culprit, but I have once again been using this all the time, especially in light polluted suburbs.
Have you been imaging with things as bright as Alnitak in the FOV? Maybe they've always been there, just not evident because of the lower intensity of the other stars?
Doug, If I cant get this resolved, I will contact Matthew Lovell who lives just around the corner and see if he will lend me a UV/IR filter, dont want to buy one unnecessarily.
As pointed out Alnitak is an extreme test but even so I tend to agree with you that your reflection is large and excessive.
As also mentioned it almost certainly coming from the flattener back to the camera. There also may be something reflective in your optical train.
Check for any bright metal parts and blacken them with a texta.
Or add some felt to the insides where you can.
Usually these reflection problems are with large chipped mono cameras
where the filters used for LRGB reflect back and forth from the flattener and perhaps the CCD window or some bright uncoated metal bit around the CCD.
Baader, FLI research and Astronomik seem to be the best for anti-reflection coatings.
Hopefully your flattener also has anti-reflection coatings as well they usually do.
A mask over the camera so only light going through to the chip helps so stray light is blocked like a baffle.
Greg, the flattener is made by Takahashi, it has reflective coatings, and I have been using it for 18 months without this reflection. Gonna be a tough one to track down.
Here is virtually an identical image shot a month ago, no large reflection on this image.
I have found the culprit, it is the damn EOS clip in IDAS filter. I removed it tonight and used a 48mm screw on type that I got a lend of, and surprise, no monster reflection. I think Hutech, would have known that bright stars can cause this internal reflection with the clip in type filters. I had my own screw in filter, which I sold when I bought the 40D which came with the clip on version filter. Hmm now I need to buy another one.
