The Admiral

Nice one there Steve, but I have to agree with Ken that your 'black' sky may be taking away some of the fainter stuff. I usually process in ST to give some background showing (heavens, it's either that or no target visible ), and then adjust the black point later in photo software to suit my mood. At least that way I can see what I might have missed. Ian

Thanks for your kind comment about my HH and Flame. If I am honest I've not done anything in particular about controlling flare; I had hoped to be able to reveal Alnitak's companion and as luck would have it is visible, but luck played a good part and I've not had to do anything special to keep it visible. I did wonder about using ISO400 to give me more DR, but in the end plumped for my usual ISO1600. "I think you've squeezed the Rosette bone dry!" Ha ha, I like that. I'm not sure I'll ever get the colours right though. If I understand correctly, the outer is Ha, and the inner is Oiii, so red and blue (?). May be more data will help. The first image is the colour that the camera sees, so in that respect is the 'correct' one. ST's colour module creates some bizarre colours as well as a fair number of green stars and I struggle to get anything that isn't too garish. For that reason I often tweak the colours in LR. Ian

I'm on a roll Here's my shot at the Rosette Nebula. The mount seemed to behave like a bucking bronco for this and I've had to discard a good proportion, leaving me only 73 x 30s usable subs. Not enough data really and framing wasn't the best, but I've squeezed what I can out of it. Heavy application of colour and lum noise reduction in Lightroom (which shows), and for the "colour" one quite a bit of work to reduce the psychedelic colours that the colour module churns out. Gear as before. No colour module Colour module I'll need to have another pop at this to add more data. Ian

Thanks very much Nige, but more luck than judgement believe me! Ian

Thanks Nige. I've had a look at adding to the number of subs, but realistically I can only add another 22, making 122 in total. I've reprocessed it, and I expect any difference is down to the processing than the extra subs. I also applied the extra luridity control (aka colour module). Here are the two results, the first without the colour module, and the second with. Colourful or what? I prefer the first one. Ian

Last night was the first clear night for quite a while where I'd be able to image, so as these moments are pretty rare I pushed on well into the night (for me!). Little dew, and a light frosting by the end of the session. First up was a re-image of M42 using short subs, because the last lot I'd taken before the New Year had poor focus. I can just about make out the Trapezium now and I'm planning to blend that with a set of longer subs, when I get a chance to process it. Next up was the Flame and HH. I took 180x30s subs, but by the time I'd aggressively weeded out the poorer ones, including some where I'd imaged a tree , I was left with just 100. The total time is barely longer than my previous attempt last March. I might try stacking more of the subs and see what difference it makes, and/or perhaps add to it later. I then spent an hour on the Rosette, though I haven't looked at that yet. So here is the first rush of the Flame and HH nebulae. Usual set-up, Fuji X-T1 through an Altair 102mm f/7 Super ED with a TS Photoline 2" 0.79x reducer/flattener. Mounted on a Nexstar 6/8SE Alt-Az mount. RAWs stacked in Astroart, processed in StarTools, and finished in Lightroom. 100 x 30s subs, ISO1600, 60 flats, 60 darks, generic bias. Ian

Coming along well with your modded camera Nige. 80° . Good grief, what sort of exposures were you using to keep field rotation in check? Ian

Thanks Nige, and I second that Ian

If in Steve's arrangement the camera faced the other way, would that help? Nige's arrangement should be able to reach balance with a single camera and heavy lens, I should have thought. Ian

Brilliant Nige, very inspirational. You've every reason to be pleased! Good nights are so few and far between, so to get anything is a bonus. Pretty fair here last night for once, and I had a good go at that old favourite, M42. Won't have time to process it though until after the New Year, as we're away . I was hoping to do some more tonight, but the gloom has descended. Ian

The other benefit of a derotator though would surely be to allow increasing the sub exposure length, and image at higher altitudes, even if the total imaging time isn't extended, assuming that the mount tracking was good enough (which I know isn't the case with my mount). Ian

You might live to regret making that offer Happy Christmas to all as well. Ian

Very nice that Nige, and I'm looking forward to you getting more frames. Ian

I was going to ask that very question! Ken's set-up is ripe for a simple transfer to EQ as most of the main issues seem well sorted. I can see you taking that inevitable step Ken . And don't feel that you need any justification! You've taken a very sensible step-wise approach to your astrophotography, keeping your options open. If only others would adopt the same approach rather than throwing everything at astrophotography in one go (as so often advised!), and then being disatisfied that they can't get the results they are seeking. Ian

Well, let's just say I've dabbled. I did a straightforward process on my M45 and there wasn't a lot of difference between that and a ST processed one. However, other things I've tried haven't been very successful. To be fair though, I've not studied it, particularly as there isn't as much teaching material around that one can dip into, as there is for ST. The modus operandum is I think more like PI, with operations needing to be performed in a certain sequence. It does seem to have a multiplicity of 'filters', most of which I haven't a clue about what benefit they bring to the table. As I found during a brief acquaintance with PI, getting colour into the image seems to be difficult. I am sure that it is fine for good subs, but when things get marginal I do find ST gives me more for less effort. At least, with my limited expertise. Ian

I had another quick attempt at processing my crescent neb, but without the, perhaps excessive, stretching I used before. It's OK, but I can't say it fills me with great pleasure, and this was from a couple of hours exposure! As I said previously, I think that this is on the limit of what might be achievable with my set-up. Stacked in AA, processed in ST, and tweaked in LR. Ian

That's an amazing image for just 15 minutes Nige, just shows how much the red sensitivity has been improved. I must look again at my crescent neb image and perhaps rein back my stretching to a more comparable image. Ian

Interesting aspect. I guess that the "Detect and Clean Remaining Hot Pixels" thniks the bright star centres are hot pixels then! I must say that in the short time I've been using Astroart for stacking, I've noticed that my 'bright' stars just look 'different'. I've not done any close analysis though. Mind you, and perhaps I'm showing my ignorance here, if you use the autosave in DSS I thought it didn't apply any curves to the stacked image. Most of us who use StarTools I guess are taking the output of DSS without using DSS to pre-condition the file presented to ST. So I'm not sure how relevant the dip in the transfer curve is here. Ian

Also, I use a 0.79x reducer on my 'scope to reduce the focal length from its native 715mm, with the aim of reducing the degree of oversampling and improving the number of photons per pixel. And it gives me a much needed wider FoV. It's still oversampling though. But in the end, there's only so much fine tuning you can do with available optical accessories. Ian

Hmm, now you're asking! . Well my take on it would be that the if we could take the 2.04"/px as gospel, to which we might add the effects of less than perfect focus, Bayer array, low-pass filter, and 'scope diffraction (which I am assuming isn't incorporated), then sky conditions would contribute the rest of the blurring. It is said that you shouldn't have significant over-sampling because I suppose you are spreading the photons more thinly than you need (though deconvolution may require some) and the camera's resolution is being wasted, so I guess that there is room to improve the situation. But, I'm not sure what effect that 'improvement' will actually bring. You need the input of a seasoned imager here, I think! But the thing NOT to do is chase the numbers. Ian

OK, then definitely NOT under-sampled! I think I've also read that in order for deconvolution to work you need some degree of over-sampling anyway. I agree with Ken, under our typical conditions you are probably not going to get significantly more detail. And with field rotation I think your best resolution is really only going to be in the centre of the FoV, as in the periphery the image will be smeared to a greater or lesser extent, depending on exposure time/location in the sky. Ian

To me I would say that they were over-sampled if anything. Is that before or after software binning? Ian

I think that probably if you are going to go on a nebula safari that you might well wish for a better red response, but obviously your choice in the end. As for under-sampling, have you zoomed right in to pixel level in ST, and do you find stars comprised of a group of pixels, or solitary square blobs? That'll tell you if you are under-sampling. Cheers, Ian

I'm running at about 1.7"/pixel, when I'm using the focal length reducer/flattener, according to astronomy tools FoV calculator. The Dawes limit is supposedly 1.14". And of course, with a OSC camera the whole thing becomes complicated and is not what it seems, especially if the sensor has a low-pass filter in front of it. I'm not sure that one can afford to get too hung up about it. Not only that, but if you up the FL then you'll end up with fewer photons/pixel, which means longer integrated exposure times. I don't think M33 is an easy target, and to me it always looks a bit fuzzy. I know it's relatively large but it isn't very bright. If you want something as 'clear' as https://stargazerslounge.com/topic/282951-m33-with-10-quattro-and-atik-383l/#comment-3096430, you'll need to remember that he's using a 10" f/4 (800mm FL) and presumably good seeing, rather better than we're accustomed to getting! I'm still dubious about the 'necessity' of a modified camera, and I know I'm going against the tide here and no doubt there are many who'll argue the case, though it does rather depend on what sort of performance your unmodified camera has. And just what you want to image. Would an modified camera help with M33? Do you want to record exaggerated reds or natural colour? Just my 2d. worth. Ian