Having recently found how well my ASI294 responds to a UV-IR cut filter on the ED72 I bought a similar filter for the SCT so I could have another go at some smaller targets. The results look promising. This is my first WIP on NGC1365, 25 X 600 second subs with darks but no flats. I am yet to work out an effective way to shoot good flats for the SCT, I have always found sky flats to be troublesome so I am trying to find a suitable screen to put a dim grey image on to be able to shoot at about the 5 second mark.
The weather is supposed to be good for a couple of nights next week so I can hopefully triple my data and combined with decent flats be able to improve the look of this one.
Ha, I did not spot that it had been picked until you posted that.
I am reasonably happy with it but want to capture loads more subs yet as I am not satisfied with the noise profile. Or the flats for that matter, the SCT is a much trickier beast to get good flats for without a flat panel. At least it is with the ASI294 which is itself a bit tricky to do good flats for. I am amazed at how well the vanilla C9.25 does on the right objects, I have still got some minor tilt issues to resolve but the Orion thin OAG is just not rigid enough on the camera side. I am not chasing the issues any further until budget allows for a new OAG. I am looking at the QHY medium format one as it has all bolted and threaded connections and the wedge/clamp connection on the TOAG is where I have a rigidity issue, and it is not set up to be able to be improved at all.
I have actually just discovered a light leak in the SCT that might impact shooting sky flats. The original fork mount holes look like they are blanked off at the base of the threads but it is just tape, and not very opaque tape that that.
I am just shooting some test darks with the garage light on as I knew it had a light leak but thought it was just a not very form fitting objective cap. Darks shot in light conditions on the SCT resulted in obvious light contamination.
It was similarly processed to the early one, though it has a problem with the flats that was a bit of a problem to deal with. I am processing it again as I type with a news set of flats so I may be able to stretch it a bit more, it needed oddball processing due to an ugly red cast on the sides that I think was due to the light leak when I was shooting dark flats.
Off to Bunnings tomorrow to buy some foil backed tape to properly black out the leaks I found, they may or may not prove to be the problem with the flats I am chasing, but they certainly impacted shooting long exposure darks.
It was similarly processed to the early one, though it has a problem with the flats that was a bit of a problem to deal with. I am processing it again as I type with a news set of flats so I may be able to stretch it a bit more, it needed oddball processing due to an ugly red cast on the sides that I think was due to the light leak when I was shooting dark flats.
Off to Bunnings tomorrow to buy some foil backed tape to properly black out the leaks I found, they may or may not prove to be the problem with the flats I am chasing, but they certainly impacted shooting long exposure darks.
I had issues with some of my early ones that was to do with flats calibration - I ended up with a circular gradient across the image. It was very difficult to fix. is your light leak circular? I am still inexperienced, but I get the feeling that nailing your calibration so you can push the image further is just as good as actually getting more data at the scope, of you know what I mean. It's amazing what you can pull out of a correctly calibrated image.
Anyway, good luck, looks like you've got some great stuff there.
Nice image being built there. Just be careful about black clipping. The histogram should have a bit of space to the left of it. Your data would show that cut off. The background should be more of a charcoal rather than black.
Yes, you are not the first to point out the black clipping, it was a bit of a compromise artifact in trying to get rid of the colour cast the bad master flat was inducing at the sides.
Markus, the impact on the flats was more or less invisible but on darks taken in daylight it showed up big curved loops of light from various parts of the edge of the frame, the holes were right back behind the primary mirror and there were six of them. I never saved the darks taken that way but I would bet that there would be an arc of light corresponding to each one. Before now I overcame it on darks by just shooting them at night but for sky flats that does not work obviously.
I am still not 100% happy but I reprocessed tonight with a new set of flats I took after finding the light leak, this was just a quick set taken with the garage lights on and the scope pointed at a wall with a couple of layers of white linen over the corrector and with about a dozen layers of gaffer tape over the holes. I could perhaps pull the background down a little more again with curves but I reckon I might stop until I gather more data to smooth the noise down some more.
