Adreneline

I would tend to go for a range over one night because at least you will end up with something you can start to process and add to over future nights. Be aware that focus positions may vary betwen filters even if they are parafocal; my experience is that blue can be a problem in this respect. If you are going to go back to the same target over a number of nights the ability to plate solve is a real bonus. I would take darks on a cloudy night and create a master dark that would suffice for all your filters; same for bias if you want to take bias. I agree flats are best taken each time but having said that if you are using a 'sealed' filter wheel you can probably get away with only taking flats periodically or if you notice something like a dust bunny on one of your integrated stacks. Dark-flats are exposures taken with the same exposure time as corresponding flats but with the lens cap on (no light on the sensor). Stand back for a whole range of answers! HTH Adrian

Well @vlaiv I've given it a go and the result is not great as the OIII has pretty much disappeared again despite massive stretching of the starless image. At least I have practised the method! I just need to grab several more hours of OIII on a clear moonless night. Simple! Thanks for all your help. Adrian

Thanks vlaiv. I'll give it a go - nothing fancy though! Adrian

I am currently producing starless versions in the hope of creating a synthetic luminance from both the Ha and OIII. Is there a correct way to produce the synthetic luminace image? Is it a simple addition process? Thanks. Adrian

Hi. I learnt how to use PI using Light Vortex. One of my first AP attempts was M31 and LV do a complete start to finish processing of a colour stack from a dslr/osc. I found the best thing for me was to make a brief note of each step/process settings, etc. Over the past three years I have worked my way through just about every tutorial. The only one that hasn't worked for me was mosaics but all the rest are really good and everything is explained with loads of screen shots to show you exactly how to complete each process. Have to say I now use APP to calibrate and integrate, PI for virtually all my post processing and PS to add the final colour tweaks and noise reduction. HTH Adrian

Ha and OIII processed separately and with added synthetic luminance with help from vlaiv.

I think this is as good as it is going to get with the data I collected. Hopefully I can collect more OIII one day soon. I decided to crop the image tgive a more pleasing picture of this target. Thanks to @vlaiv for all the help in pointing me in the right direction to extract more detail; it's been quite a journey and a great learning experience. Adrian

I figured out how to do your maths in PixelMath and this is the resulting image, saved as a png so as not to introduce more noise/artefacts. It was very noisy so I've reduced the noise level in PS; the colour saturation and brightness has definitely increased. I had to convert the synthetic luminance to RGB and then extract the channels as L_R, L_G and L_B. I did the same to the HOO image saving them as R, G and B. This is the PixelMath dialogue: I think I need to start again now I know where abouts I'm heading. Adrian

A Bad Pixel Map created by APP. Right! I shall have a play around with PixelMath and figure out how to do this. I suspected my method was too simple! Watch this space! Hopefully I will get my next offering up this evening. Many thanks again for all your help and guidance - this has been a great learning experience for me. Adrian

I've pushed the colour a bit more @vlaiv - not sure it's an improvement though.

I used flats created immediately after imaging and corresponding dark-flats with darks and a BPM - all in APP. Not sure I understand this - I combined Ha and OIII using PixelMath with Ha assigned to R and OIII assigned to G and B. For the first image above I literally added synthetic luminance to the HOO image - no scale factors or anything - which resulted in it looking washed out. The second image in the P.S. was tweaked in PS using Selective Colour and a Hue/Saturation layer. Adrian

Well I have had a go @vlaiv at recreating your methodolgy in PI. OIII is binned 4x4 and stretched to breaking point. Ha is cloned and moderately stretched for 'colour' and more aggressively stretched for luminance. Ha and OIII combined as HOO in PixelMath and then synthetic luminance added to the end result, again in PixelMath. I then adjusted the black point in HistogramStretch and moved the 'mid-point' to the right to increase the contrast. The resulting tif was moved to PS for modest noise reduction. The end result is not as vivid as your rendition but it provides an interesting contrast. Perhaps I need to experiment with Selective Colour in PS to see if I can change the hue/saturation. I will have another go using Starnet++ before I stretch the OIII but that means using the PC rather than the MacBook (I just cannot fathom Starnet++ in Terminal on the MacBook). As ever I would value your comments - good and bad! Many thanks. Adrian P.S. This has been coloured up a bit in PS.

Wow! Thanks vlaiv. That's very interesting and I will re-visit the data and the process and have a go myself. I have to say the main object of the imaging exercise last night was to check out the performance of my new 6nm filter with the 135/1600 combo and make sure I could achieve focus correctly with the spaceing I had set up. When I came to use the OIII the conditions were going down hill and the focus position was not optimal either as the focus position was not with the 'L' on the lens. This was entirely due to mixing filter types - Astronomik Ha (1mm thick) and Baader OIII (2mm thick). I knew I was pushing my luck trying to extract a HOO image but it was worth a go. Nothing ventured, nothing gained. I clearly need to save my pennies for an Astronomik OIII as well! Really appreciate you taking the time to do this. I will have a go and see how I get on. Adrian

Absolutely correct! I actually took 20 x 120s but only the first eight were worth keeping; high cloud rolled in earlier than forecast and the moon glow spoilt the rest. Thanks for looking. Adrian

Hi vlaiv Here are my calibrated/stacked and registered (but not cropped) fit files for Ha and OIII. Many thanks. Adrian H+S-960s-OIII_r.fit H+S-2280s-Ha_r.fit

Hi Gina, This is what Light Vortex has to say on the matter: " The PixInsight process responsible for this feat is LinearFit, which assumes that a mathematically linear function can model the difference in average background and signal brightness between a reference image you choose and the target image you apply the process to. As a result, it works best at the very beginning of your post-processing, when your images are linear, but strictly speaking it does not need the images to be linear for it to do its job. Please note that LinearFit requires that the images it is applied to are registered to each other, otherwise there is no correlation between the image we set as reference and the image we apply the process to. " See this page for a more complete answer. Adrian

I'm in that club too! I only know of one "expert" in PI. I think PI is a bit like quantum mechanics Adrian

Thanks vlaiv. That is really useful to know. In the tests I've carried out so far I find it really hard to distinguish between pre or post stretch but that may be due to other inadequacies in my processing regime. My experience is that 'processes' often are quick to say what they do and not so quick to say what they don't do! Use with care! The provider accepts no responsibility, etc., etc. Thanks again for your 'qualified' advice - it is much appreciated. Adrian

Thanks vlaiv. Light Vortex also advocate using LinearFIt for broadband imaging but recommend combining before stretching - the opposite of the advice given for narrowband. Would you recommend dropping LF for broadband as well? I've not tried synthetic luminance before - I will give it a go and see how I get on. Many thanks. Adrian

I know there are a lot of these images on offer at the moment but I will add this one to the mix and seek advice/opinions on combining Ha and OIII. This is 26 x 120s of Ha plus 7 x 120s of OIII. I had every hope of getting more OIII but the clouds had other ideas. The subs were integrated in APP and then processed in PI. I used StarAlignment, DynamicCrop, ABE (subtraction) and finally LinearFit before combining in PixelMath as RGB : HOO. Light Vortex recommends applying HistogramStretch (or whatever stretch process you prefer) before combining but this seems counter-intuitive to me because LinearFit has supposedly equalised the background levels. Any form of stretching is almost certain to result in background levels being different making it more difficult to remove any resulting colour cast. The question is should I combine and stretch or stretch and combine? What is the perceived wisdom when combining narrowband channels? Thanks for looking. Adrian

Used my Samyang 135mm and ASI1600 with my new 2" Astronomik 6nm Ha filter for the first time last night (delivery of new filter and clear night on the same day!). The results, to me, seem very encouraging. Had the usual game of finding the exact spacing to give star focus with the focus mark in the middle of the 'L' but I got there in the end. This is just Ha with very minimal edge cropping. The image is stacked in APP and processed in PI with minimal final noise reduction in PS. I also took a few frames of OIII with my Baader 2" filter. The focus point for the Baader was significantly different to the Astronomik and well before the 'L' mark on the lens. This is pure HOO. I combined the images in PixelMath before stretching. Light Vortex recommends stretching and then combining but that in one respect seems counter-intuitive to me. Having applied LinearFit to equalize the background it then seems right to combine. If I apply Histogram Stretch and then combine the chances of the backgrounds being the same are slim and I am sure I read LF works best on linear images. Anyway, here it is: Adrian

An awesome result Alan - the time and effort invested has really paid off. Love the colours and the clarity of the whole image. Excellent! Adrian

Ordered yesterday, arrived today (brilliant service again from @FLO ), installed in the filter holder, gear setup outside and foucssed with BM and now collecting amazing images of Heart & Soul - and not a cloud in sight! How lucky am I? Adrian

Hi Frank If you go to the Affinity Photo forum and type in 'astrophotography' in the search box that will throw up some macros, etc. Typing 'astro' in the search throws a bunch of discussion threads that are ongoing. You will need to login to access the forum. HTH Adrian

I can't help with the cause of the artefacts/dots in the image but have you tried using something other than PI - like Deep Sky Stacker? I usually stack in APP these days but if there is something odd in the resulting integration I often throw it all into DSS to see if I get the same effect. It's free, dead easy to use and worth a go - unless you're Mac only and don't have access to a PC. Adrian