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I've been imaging Thor's Helmet for the last couple of nights in Ha and O3. I notice that RGB data can be used to correct star colour. What exposure is recommended to capture the stars and how many should I take? It looks as if I've one more clear night for the time being. Thanks Anne
Hi guys With the weather here in the UK being so bad recently, and with work commitments and other boring life stuff going on I haven't done much imaging lately, but I did finally manage to get out and grab some OIII data a couple of weeks ago to go with my old Ha data of NGC 1499 from back in September. The Ha data was from first light for the newly modded D5300 and Baader Ha filter. We have an outdoor sports facility only a couple of hundred yards from our house, and annoyingly the ridiculously bright floodlights don't turn off until after 10pm on weekdays, so even though there was no moon to contend with, I had no choice but to wait until the lights were off before I could start shooting the OIII. I thought about shooting more Ha while I waited, but in the end I decided to shoot some short subs without any filter, just to use for RGB stars. I stupidly didn't use my IDAS-D1 filter, and the scope ended up pointing almost directly at a streetlight for all the RGB subs. The result was a stack that had a simply insane gradient running through it, and which made gradient reduction on the stack impossible, as it was changing so much between subs. In the end I had to run gradient reduction on each individual RGB sub before stacking, and then run it again afterwards! Thankfully I only shot 20, so it wasn't too laborious. In the end I had something which, despite having a really ugly background, did at least have useable stars. As for the OIII, boy was the signal weak with this one. I'm used to dealing with weak OIII signals on the D5300a, but this one really took the biscuit! Thankfully J-P Metsavainio's tone-mappng technique allows one to get the sledgehammer out for such cases, so I was able to stretch it far enough to get something out of it (even if it doesn't yield any fine structural detail for the OIII). So this is 23 x 8 min Ha, and 9 x 20 min OIII subs. Calibrated with Flats and Bias, and dithered aggressively. The stars are made up of 20 x 90s subs. Everything shot at ISO 200. The usual gear was used, HEQ5 Pro Mount, SW 80ED (with FF/FR), guided with PHD2 and a Finder-Guider and Legacy QHY5. Captured with SGP, pre-processed in APP, and processed in PS. I have to say, I really like having the stars in a separate layer in PS. So much so, this is how I'm now going to process all my images from now on. It makes things so much easier being able to adjust whatever I want and not have to worry about constantly protecting the stars. I'm not actually finished processing this one, but I thought I'd post it up for now anyway, and update it later. I still haven't ran any noise reduction on it yet, so I need to do that next, but hopefully the final version will not look much different to this. I did have some fun playing with the colour on this one. I have noticed today though, that it looks quite different on my work Dell monitor compared to my cheap Korean one from home. I think it looks a bit duller today, but I'm just not sure! What do you guys think, does it need more or less of something in particular? All comments welcome, I'm always looking to learn! Cheers all!