Xiga

Hi Mark I wish you well with this, as it's one of the most amazing objects to image in the night sky (imho) and i would love to shoot it myself. I too have a 135mm lens and a crop sensor DSLR. However, and i don't mean to be a wet blanket here, but i think this is going to be a tough one. I don't know what your latitude is in Wales, but here in N.I i am at 54 degrees N. Which means R.O never gets above 8 degrees altitude. To make things worse, it's a late Spring target, when dark skies are at a minimum (in fact there is no astro dark then, just astronomical twilight). I've done a bit of research into this, and the only time that's even feasible for us here in N.I is the beginning of June. At that time, there will be no moon, and there is just about 2 hrs of Astronomical Twilight around the time when the object transits. So if you have a very clear view of the Southern horizon, and the weather plays ball, then this is your best time to try and catch this. FWIW i'm not even sure i can see 8 degrees altitude to the South, the neighbour's house is probably in the way ☹️ Here is a great website for checking how much darkness there is on any day of the year. The link is for Belfast, so you'll just need to alter it to your nearest location. https://www.timeanddate.com/sun/uk/belfast Good luck. Hope you get it!

I like that Adam. I love these widefield shots with the main stars accentuated so you can more easily see the outline of the constellations. Betelgeuse is looking lovely too! Just one small bit of feedback - the stars look a little green on my monitor. I'd maybe try a quick pass of HLVG on a colour layer to see if it helps. ps - Is that a meteor you captured as well, just above Betelgeuse?

Amazing. So much detail, with just the right amount of saturation, and the stars are as good as perfect too. Very good indeed!

Did you use APT for all of the subs? Lights and calibration files? It sounds like Gain is a recent addition to the Fits header info. Clutching at straws a bit here, but you could maybe check your APT Log file with a fine tooth (no pun intended! lol) comb. Look specifically for Gain and Offset values for all the calibration files and Lights and make sure they match. Or if you'd like i'd be happy to take a look at the data for you, just to see if i get the same outcome. Even just a subset of the full data should suffice. Say 10 subs of each would do.

Not being a CCD user, i'm not sure if any of this is material or not, but i notice in the Fits header info that the Gain for the Darks is 0, but it's -1 for the Flats and Dark Flats. Also, the temp of the Flat is about -1 degree C colder than the other two. Could either of these be the culprit i wonder? I would at least try and get the temp of the Flats a bit closer, just in case that's it. I don't see any info regarding Offset. Are you absolutely sure all of the files (both calibration and lights) have been taken with the same Offset? Weirdly, only the Dark has an entry for 'Telescope' in the fits header info. The other two are missing this option entirely. It's a strange one alright. But right now my hunch is that there's nothing wrong with your optical train or gear, and that the most likely reason is just something silly that's gone wrong during acquisition of some of the subs.

That's a good point Adam. APP is now 'smart', so it is supposed to handle the files automatically for you. I still manually select mine one batch at a time (just because I've been doing it that way since the earlier versions, and, well, I'm on old dog, lol) so I don't know how well this functionality works. If you throw it files it doesn't actually need, will it ignore them? Or does it just know how to handle all the myriad calibration files, assuming you've selected all the right ones to begin with? Not sure tbh. Another tip for you regarding APP - you don't need to finish a stack to know if calibration is working or not. As soon as you've finished Step 2 (Calibration) you can select any Light sub from the list at the bottom, and change the drop-down box at the top of the screen from 'Linear' to 'l-calibrated'. This will show you what the Calibrated Light sub looks like, and it should be obvious if it's working or not. If the Bias files don't solve the problem for you - thinking outside the box here - you definitely haven't mixed up your Atik and QHY flats by any chance?

Hi Adam I think @vlaiv is right about the Bias files. I don't use Darks myself with my DSLR (although I keep meaning to run some more tests on that) however, it is my understanding that if you are using Dark Calibration files, then you should not also use Bias files, as I think it will remove the dark current twice. So it's probably over-correcting at the moment. Try without the Bias files and see how it goes.

Stunning as always Richard. You certainly know how to process the dusty stuff!

Here are my 5 best of 2017. Actually, aside form a couple of others, it's pretty much my entire output from 2017, lol. The biggest change for me this year was, getting the D5300 modded and picking up an Ha and OIII filter. I also picked up a cheap mono camera (IDS UI-6250SE) 2nd hand for doing Lunar work, which i used for the mosaic below.

Hi Mike The one I've been using is called Remove Stars (Large Image). Good luck! ?

Just to be clear, i have only been using this on OSC data, so the images have all been set to RGB mode in PS. There is no separate background layer. So when you create the starless image, it becomes the bottom layer. Then put on top 2 identical layers of the regular non-starless image. All 3 layers blend mode should be on Normal at this stage. The you just need to change the blend mode of the top layer to Pin Light. Finally, as Tim pointed out, you then need to adjust the opacity of the MIDDLE layer down a tad (e.g 60-80%). In addition, i don't think it does remove the colour data from stars. I don't have any especially high-quality RGB data to showcase this on, but i've shown a crop below from an old M33 image i did a year or so ago, which had some very large stars, and as far as i can tell it doesn't reduce the colour.

The starless layer is definitely at the very bottom. But you're right that the blend mode for it doesn't matter, so you can just leave it on Normal. Sorry if that wasn't clear!

Did a little more playing around with this, and noticed something that i didn't before. The technique also seems to darken any extremely bright areas of nebulosity. I've shown a tight crop from an image below which shows what can happen, so care does need to be taken when using this method. FWIW, the image i'm working on at the moment didn't have too many areas that were affected, but i did have to use an extra layer and the eraser tool to clean up the affected areas. ps - i don't know if it's just me, but i could swear that this method does also improve the sky background slightly too. I have been using it on DSLR Narrowband images, which are obviously noisier than most, so perhaps it's proving more helpful for that reason, but i do think that it darkens some low-level noisy pixels that are just a tad lighter than their neighbouring ones. I can't say for sure though!

Hi Tim After playing around some more, it would appear that the starless layer at the bottom is not of paramount importance. But of course, you still want it to be as good as you can get it. I recommend Annie's Actions, they're not expensive, but i also have another source for a PS action to remove stars. I came across this one a while back, it's just a small action set made by a guy who offers it for free, and it includes actions to separate stars from sky background, i've attached the link below. I compared it to Annie's Action, and it doesn't do quite as good a job, as it doesn't really remove the big stars very well, but it still works quite well and it's certainly much better than having to do it from scratch. http://troypiggo.blogspot.co.uk/2010/11/troys-astro-actions.html I've also discovered that the blending mode of the starless layer makes no difference, so you can just leave it on Normal. The blend mode of the middle layer does matter, and needs to be kept on Normal (for info though, Luminosity, Lighten and Lighter Colour all work exactly the same too). But the top layer absolutely must be set to Pin Light. I'd be interested to see any before and after images that you try it on.

And here's a quick before and after M42 crop at 300% Think this technique might be most useful on the really biggest brightest stars. ps - you really need to flick back and forth on the images, and not just view them side by side at the same time, to see the full effect

Hey guys I know we all have our own favourite way of doing star reduction (i have used Noel Carboni's action, and i also like using the Minimum filter in PS too) but i think i may have stumbled across another new way, and i actually quite like it! The NC action tends to darken the image a bit, and it also doesn't seem to work well on extremely large stars, and the minimum filter does tend to soften the stars a bit (which can look quite nice, depending on the image) but this technique, if anything, actually seems to tighten up the stars, and you also get an Opacity slider to play with as well, so you can set as little or as much of it as you like. Also, the minimum filter tends to obliterate really small stars, whereas this method doesn't seem to at all, so depending on what you are trying to achieve this hopefully might prove useful to some. So here goes: 1. Create a 'Starless' version of your image. For this i use one of Annie's Actions and finish it off by using the Spot Healing Brush on any remaining star remnants. 2. Put this Starless layer at the bottom and set the blend mode to Colour (the blend mode isn't critical here, especially if you've done the starless image carefully, but using Colour will always ensure you don’t lose any hard-earned detail). 3. Add your Master Luminance (or what you had as your pre-star-reduction image before) on top of the Starless layer. Then duplicate it so that you have 2 of them on top of the Starless layer. So 3 layers in total. 4. Now change the Blend Mode of the Top layer to ‘Pin Light’. 5. Finally, bring down the Opacity of the Middle layer. 70% - 80% seems to work well, and can have quite a big impact, especially so on really big stars, but i wouldn't go any lower than this. I've shown a Before and After example below so you can see the effect. (apologies for the lack of resolution, it's from a very severe crop!) But i'd be really interested to see what others think of this, and whether or not the technique can be improved , or even if it's just to find out if it's actually no good at all! (i have no way of analysing images statistically, i simply rely on my own 2 eyes! lol). I know my way around PS pretty well these days (all thanks to AP) but it's basically all down to trial and error, so i don't consider myself an expert by any means. Just wanted to let people know that in advance!

This is great, thanks Mark! Quick question: do you think there would be any benefit to using this approach just to create a stretched image for use as Colour only? In other words have 2 completely separate images, and stretch the first one (however you normally go about doing it) for use as Luminosity, and then stretch the 2nd image using the above approach and use it just to colourise the Luminosity image. The reason I ask is, when I used the Gamma curve approach it appeared to me that a lot of the Green noise (i.e pixels) got removed, similarly to what HLVG does, but a side-effect to this was that the background then became more pockmarked. Processing colour separately to Luminosity should cure this. Thoughts?

I'm not sure if this is the reason Tim, but it looks to me like you've done your Exposure and Curves the wrong way round. You want the Exposure Layer showing as being *below* the curve layers.

You were quite right Mark, PS was indeed doing the weird posterization thing on me. Although on my system it was a little different, it would show things correctly at any zoom level above 63%, not just at 66% and 100% specifically. I'm using PS 2014 CC. I tried lowering my cache down to Level 1 but, while it did indeed get rid of the posterization, i found the overall slowness unbearable tbh. And i'm using an SSD as well! In fact PS even crashed on me while i was using it on Level 1 cache. That's the 1st crash i've ever had in the 3 or so years i've been using it, so i had to go back to Level 8 myself. It wasn't that big of a deal though as all i had to do was keep the zoom level above 63% As far as actually getting the stretch to work properly, the issue i was having originally was that i wasn't grouping the layers (Grey Multiply, Exposure, Curves) as you showed in your last picture. I was just changing the Blending Mode of the Grey Multiply Layer to 'Multiply' as you said in your original post, but it wouldn't work for me until i grouped them all together and set the overall Blending Mode to 'Multiply' (the default was Pass-Through and it also didn't work for me). Anyways, just thought i'd let you know, and thanks again for this, it will completely revolutionise how i process my images from now on! ps - I'm just noticing some slightly pinkish star cores. Got any solutions how to fix that?

Hi Mark Okay i had another go and actually had some success this time. And WOW, what a difference this colour-preserved stretch makes! I'll cut straight to the chase and post 2 pics below. The 1st one uses a regular stretch using multiple iterations of curves, and the 2nd one uses your colour-preserved stretch method. I tried to get the histograms as close as possible on both. Although there was a very slight difference, it didn't affect the comparison. These are crops of an M33 stack i did last year, and the stack had already had gradient reduction and colour balance applied. The difference is nothing short of remarkable. Right throughout, the colour of everything has been maintained. I used a Gamma of 2.5 as you suggested, and i think i used 2 or 3 curves. What's more, i was expecting to see an increase in the background colour noise, but it's the exact opposite! The red blotches are significantly reduced and, for whatever reason, the green blotches actually look like they are now 'missing' from the image. Honestly, looking at the image, i would have guessed that HLVG had been ran on it, but it hasn't! Is this normal behaviour for a stretch like this? I did find a quirk in getting the process to actually work, i'll write another post next to explain. Amazing work Mark to figure all this out for us PS guys who haven't moved over to P.I yet (in my case due to cost).

Hi Mark I had a go at this last night but I couldn't get anywhere with it. I also have PS CC and my steps looked exactly as per your picture above, but all I could get was a massively blown out galaxy and very strange stars, everything was basically white. I forgot to take a screen grab of how it was looking, doh! Do you have any ideas what was going wrong? Would it help if I posted a link to the stack?

Top stuff Mark. Thanks for explaining that, it makes perfect sense now. Hopefully I'll get a chance to test this out on some old M33 data tonight. If I do I'll try and post up a comparison to just doing a bog standard stretch.

This looks great! I'm a PS guy so I can't wait to have a go at using this. Quick question. The example you gave used just 1 gamma adjustment and 1 curve. Normally when i do my stretching I do each one in small to medium amounts, so it can take quite a few iterations before I'm done. How would the gamma adjustment work in such a case, should it always be in the region of 2.5 or would it need to be lowered significantly? I'll do some experimenting myself to be sure but would like to hear from the expert all the same ?