I did my best image a few weeks ago, of Orion (on literally the only other cloudless, moonless night we've had for about 17 years). Achieved it by getting stacks of different ISOs - ie 25 x ISO 800, 25 x ISO 1600 etc - and exporting different versions of them (lighter & darker) from DSS, then stacking the resulting processed TIF files, then using Photoshop to combine various elements. Worked great.
Tried the same thing again tonight on last night's capture of Omega Centauri. Not thrilled with the result. For one thing, the colour was all over the damn place from stack to stack. Not seen that before. Maybe a neighbour's back yard light came on and threw off the white balance. Or maybe it's just my cheap DSLR behaving like a cheap DSLR.
Anyway. Any thoughts / suggestions for improvement welcome. Cheers!
Chris, it's actually not a bad result. You've picked up star colour which is hard to achieve on this object. When you say " I tried the same thing again tonight ", I assume you're referring to varying exposure lengths and iso values with the subs you're stacking. It looks like you may have overdone the shorter exposure/lower iso subs, thereby preventing the capture of the smaller, fainter stars in the cluster. Maybe try restacking your subs with less of the shorter subs which will let the longer exposed subs display more of the fainter stars. Your polar alignment looks to be a tad out too but overall it's a pretty good shot. The colour change could be due to high cloud drifting past during your session which may not have been discernible to the naked eye but becomes obvious as you flick through your subs.
What is your field of view like? Is that image your full frame or have you cropped it? If it is cropped, I would have a go without cropping unless you have field curvature or another issue that makes things look muddy full frame.
I have always found Omega Centauri and 47 Tuc to be more appealing targets visually in wider fields that pull the mass of stars together more tightly.
Yes, the image is cropped to around 50% of the original. Stretched stars get worse the further from center you get. (Couldn't be bothered setting up guiding principles even doing a proper drift align because I was only planning on 20-sec subs.) Also really just wanted the cluster on its own as I already have several wider-field images from my ED80. So yeah, cropped for both practical and aesthetic reasons in this instance, but I know what you mean.
Re the blending of different brightnesses, I think you're right - kinda went overboard with reducing the core brightness which took the fainter stars down further than they should be. I'll have another go at blending them.
Re colour, there were no clouds at all (I checked all subs before stacking) - just changing the ISO resulted in startlingly different tints. I honestly think that's just the camera - I've used my high end full frame cameras occasionally, and have noticed a massive improvement in colour rendition at high ISOs. They nailed the colours of Trifid whereas this thing just made it all red and purple. Just prefer this one for its crop factor, so guess I'm stuck with it for now...! I think I need to try to get the different stacks closer in colour, but DSS isn't the best program for fine tuning colour accuracy.
I'll have another shot at processing and editing and will report back. Thanks again for your feedback.
