Adreneline

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

I’m a fan of BYEoS and the focus aid is great. Others will advise APT which is much cheaper and more versatile and has a variety of focus aids. I seem to recall that if you go to the BYEoS site it gives you the optimum ISO to use for each Canon camera it supports. Excellent first image though - loads better than my first attempt. Well done! Adrian

Wow! Well that gives a completely different perspective on things. Which bit in particular are we looking at? Very nice stars - the RASA8 appears to be doing a great job for you. Thanks for sharing. Adrian

The situation with PS is now worse for Mac users. I purchased an education licence of PS CS6 Extended for Mac some eight years ago (~£180 instead ~£950); it has been used extensively for regular and astro photography over the years and I've certainly had my monies worth. However, with the introduction of Catalina things have gone pear-shaped. If you upgrade a Mac to Catalina in will advise you that certain pieces of software on your computer will no longer run and will be removed as part of the upgrade process. One of those piece of software is Adobe Photoshop CS6! I contacted Adobe and asked if I could exchange my Mac only licence for a Windows PC licence - response "No". When my 10 year old iMac and 7 year old MBP fail that will be the end of my Photoshop. I absolutely refuse to pay more to Adobe. Adrian

I am sure it is but when you buy a ZWO camera it comes with a whole bag of shim type spacers as well as various metallic spacers with various threads - unlike an Atik camera which in my experience comes with nothing! Adrian

Without my 0.75mm of spacers the 'infinity focus' position was before the 'L' mark and I had significant star shape problems in the extreme corners of the image with very noticeable 'coma' type star shapes in the top right and bottom left of the image. If I add another 0.25mm spacer the focus point moves beyond the 'L' mark. I cannot be certain my current spacing is 'perfect' but the star shapes are acceptable (to me). On modern lenses the lens can be set to focus beyond infinity - although I am not sure exactly what that means. As a final complication the focus point is different for all my filters. Using the ZWO EAF as a reference the focus position varies from 28302 to 28382. Now I've not done the maths to work out exactly how much that has moved the focus ring on the lens but I do know that even at the extremes it still stays within the 'L' so I am happy I've got it about as good as I am likely to get it without becoming obsessively compulsive about it. I hope this helps. Adrian P.S. As a footnote I spent two entire evenings stripping the camera and lens apart and messing around with an array of spacers before I got to where I am now. I'm in no rush to change anything! Good luck!

Hi Carole, I found it very difficult to get a combination of spacers that allowed me to get the 'infinity' focus position in the right place, i.e. within the bounds of the 'L' mark on the lens focus ring. In the end I had to take a 5mm spacer and grind it down using a belt sander (! - nearly ground my fingers away at the same time!) until it was just a shade over 4mm. I had a 3mm ring spacer but that wasn't enough - a 5mm spacer was too much. My experience is that the spacing is super critical. In my current setup I have 0.75mm of spacer between the EFW and the ZWO 16.5mm spacer; if I remove the 0.75mm the focus point is before the 'L' on the focus ring on the lens. I know the quoted spacing is 44mm but my experience with this lens, filter wheels with filters and astro cameras is that 44mm is a good starting point but it will not give an optimum focus position within the 'L' mark. I had exactly the same experience with the 85mm lens that I used to demostrate the effect of gravity!! I also understand there is a tolerance on the 13mm quoted on the camera but I am not confident to quote the figures I have seen. Theory is one thing but as with most things in this game it is careful experimentation that generally gives the best solution - and that coming from a theoretical physicist! I should go wash my mouth out. Adrian

The distance from my Samyang end plate to the camera sensor is 46.25mm and that takes account of the 1.25" Baader filters I use. I currently use the lens with a ASI1600 (6.5mm backfocus) but I have also used it with difficulty with an Atik428ex (13mm backfocus). This site gives some useful info: "So the first thing you need to do is check to see if your lens has an ∞ symbol printed on the barrel. Some lenses actually have an additional marking that tells you how far you need to go backwards after that hard stop in order to focus to infinity. This is typically shaped like a sideways “L.” If you line up the distance indicator (a vertical line) with the infinity sign, you won’t get the correct focus. If, however, you line it up with short vertical part of the “L,” you’ll be focused to infinity. Theoretically. Remember that if you’re off even a little it could mean the difference between tack-sharp stars and pancake shaped stars, so you’ll need to double check using the method below." My lens focusses here:

Looks great and excellent framing. If you're open to suggestions, if you lighten the background a little to R:G:B = 23:23:23 (advice I received on this forum), or thereabouts, even more of the hydrogen and outlaying nebulosity starts to appear and the background sky looks more natural and less clipped. As already suggested incorporating Ha into Red as a lighten layer can produce very pleasing results - worth a shot perhaps. Adrian

Very nice! Looks amazing to my eyes - love the colours - not too overstated. Adrian

Thursday night was quite fruitful in many respects. This is a two pane mosaic of the Rosette and Cone taken with the 135/1600 combo. Lens at f2.4 : camera at gain 139, offset 50, temp -20 degrees. Each pane is Ha, 10 x 180s unguided. Preprocessed and stitched together in APP; background extracted and histogram stretched in PI. Adrian

Exactly why I have gone for the iOptron CEM25-EC + ASIair to use with my Samyang/1600 combo. I can be setup and ready to image in less than 15 minutes and the ASIair plate solving is a godsend when it comes to repeatability to build up an image databases for these feint target. All I need now is the portable 12V supply and I am good to go. Question is which 12V power pack to go for?