ollypenrice

Sensitive processing. It's so important not to bring the black point in too far because the ultra-dark dust lanes are so easily clipped. These are spot on. Olly

I don't have the groups facility in my stacking programme but it is a good idea and should let the Sigma routine work as if all subs were from the same run. Olly Edit: For anyone else without a 'groups' facility you have the option of calibrating all the subs with the right flats and darks without combining them and then stacking all the calibrated subs without further calibration. That will have the same effect.

Let's assume you can use the same darks and flats for both runs. To some extent the choice between 'stacking the two stacks' and stacking the lot in one go depends on which stacking algorithm you're going to choose. If you're going to use a Sigma Reject algorithm, which is very powerful, then the more subs in the stack the better it will work. It's looking for rogue pixels, outliers from the norm, so the more subs you have, the more successfully the algorithm can establish a norm, and so identify the outliers (which will be awarded the average value of the norm.) If you have a sat trail in an otherwise good sub, for instance, and you have a lot of subs in the stack, the rogue values of the trail will be overwritten by the average values of the norm in a Sigma routine. The trail will vanish. The same is true for random residual noise after dark subtraction. Since it's random it isn't part of the norm and will be over-ruled by the norm. So if using Sigma it is certainly best to restack from the start. (If you use a simple averaging algorithm the trail will be 'diluted' by the averaging but not excluded.) If not using Sigma it still has to be mathematically better to stack from the start as well, but less so. You may not notice much real-world difference. Do stack from linear in all cases, though. I would always restack from scratch and use a Sigma routine if the calibration files were applicable and the images from the same scope. Olly

Super image. Really good. The colour looks stronger in the LRGB than the RGB, maybe because you continued to push the colour after or during the combining with L? Olly

Good progress on the processing. Olly

It's all in place but for me the noise reduction is very intrusive. I wouldn't be frightened to leave a little gain in the image. Olly

Crisp and contrasty image. Olly

Nice star colour, too. Olly

In support of this observation the 'shuttlecock' artifacts are predominantly red, suggesting that the lens is not controlling those newly active deep red wavelengths. Note that the shuttlecocks are all orientated as if racing away from a roughly central point, strongly suggesting an origin in the lens. Origin

It's a rather special instrument because it isn't bought for its performance but for its charm and, I suspect because of its astonishing price rather than in spite of it. (So the question arises, does the Questar buyer actually want to pay less?) I always think of it as astro-jewellery so I suspect the market will be quite unlike the regular astronomy market. Olly

This comes up regularly. To clarify, the formula stating that exposure time increases as the square of the F ratio is predicated on having a fixed focal length and a variable aperture, meaning that aperture is the 'active ingredient.' On top of that we have to consider pixel size because what really determines exposure time is the ratio of objective area to pixel area. And on top of that (oh no!) we have to consider 'regions of interest.' At short focal lengths we may end up capturing an enormous amount of sky in which we are not interested and concentrating plenty of light from our target onto too few pixels. Professional telescopes are often of slow F ratio but work very quickly because they have large aperture and large pixels. Olly

You can't safely compare F ratios at different focal lengths. Oly

These are dusty targets which always need very substantial integration in order to come out looking smooth. In fact they never really do because I suspect the dust is naturally grainy. The Iris shows that the second image has had a harder stretch which goes with its higher noise. I think you just need much longer integration on this kind of target. Olly

Typing paper works fine as a dimmer and can be adjusted easily by adding or removing sheets. With a CCD you don't need dedicated flat darks, you can calibrate your flats by using a master bias instead, though the flats exposure shouldn't be too long if you do that. Olly

Sounds right but if you have a filter of x mm thickness in the train then add 1/3 x to the extension. Olly

Result!

Purple? Seriously? It's slightly magenta but I didn't 'go for it,' I found it in the data when the sky was calibrated to parity and the bright stars compared with their spectral classes. Obviously you can trawl the net and find any colour scheme you like but that is hardly a constructive way to inquire into what agrees with the astrophysics. We don't ascertain the date of the battle of Hastings by voting on it. The Hubble team are pretty serious but, unfortunately, they concentrated on the core. This is a warm colour with the spirals striking me as a mid blue. Since they can out resolve everyone else their blue stars will be held more towards to points than amateurs can manage so the blue will be less diffused into the arms. The Hubble image is done in broadband colour and many amateurs will add Ha which, obviously, will slew the blues towards longer wavelengths in exchange for picking out interesting structures. When this is declared it seems perfectly legit to me. Olly

It looks like a miscollimated lens to me, at first sight. Olly

Tom has now posted a 'zoomable' version of our Orion on his website. This is the best way to see it. Put the image to full screen first. https://www.astrophotography.ie/mosaics.htm Olly

Rather than use a pinhole star test why not use the classic ballbearing method? Glue a ballbearing (EG from a bicycle wheelbearing) onto a black card and prop up a torch to shine on it. Observe this from as far away as possible but it will work at 10M. Only light from the bit of the BB closest to the objective will be reflected back towards it so you get an excellent artificial star. Olly

Have you checked that the filter will work OK at this F ratio? Just a thought... Olly

In rather doom-laden era it really is great to see FLO thriving and employing new staff. Well done. Behind your update lies a phenomenal amount of professional retailing skill and creative thinking. Round of applause! Olly

Head-banging pursuit of that outer shell! (I wouldn't really chase as hard as that but this was just for the hell of it.) I couldn't find much star colour but it isn't very intense in my long exposure version either. Olly

I've used tappng for revealing star colour. I don't think I've tried it for going deep. I'll give it a go. Olly

Do you really need a long focal length? Since pixels are getting so small you can hit the useful 0.9 (ish) arcseconds per pixel scale at a metre or even less. If you want to stick with larger pixels or bin 2x2 how about an 8 inch Edge? Olly