ollypenrice

True. I think the N and H must be showing through the core which is saturated in O. That wouldn't work if the O were used as luminance but it will be getting only about a one third weighting if combined as a colour channel. I reckon even just one non-saturated O core would save the day. Olly

Extravagantly splendid! Beautifully crafted. Olly

I had another look at Dave's posted OIII stretch and it's certainly saturated in the same place, Dave. The screen grab goes off the scale in Curves if you mouse over it. (I've found that screen grabs are quite reliable where the histogram is concerned. I've tried uploading and screen-grabbing an image of my own to compare the grab with the original and found them equivalent.) However, I'm puzzled by why this should have happened, especially in the light of the comparison you make with your own linear data. Maybe it has had a stretch somewhere? Or is this some CMOS mystery like gain? Does the FITS header tell you what the gain was? I'm just wondering if it might accidentally have been set too high. Olly

Dave, I was all set to get cracking on an HOO because the OIII shell looked brilliant. However, the OIII stack as it is isn't workable. It has a significant patch which is fully saturated and contains no information as a consequence. The crop below is linear. This comes as a surprise, particularly in narrowband. Could it be that you were shooting in moonlight some of the time? The background sky is quite light so that might have eaten into your well depth. If so you might be able to make a separate stack of just the darkest subs and use it as a repair patch. You wouldn't need a lot of subs to get a good S/N ratio because the region is so bright. Failing that, you'd need to shoot a set of short subs to fill the saturated parts, as is always necessary for M42. Olly

That would be the day we drained and refilled ours with one last charge of clean water... Olly

'Yes I guess what I was trying to show was that the amp glow and dust from the first images was gone.' Yes, but so was about half of the image! My standard advice is always, and without exception, look at the image. So, if you look at the image above, what do you see? What I see is a decent M33 sitting in a dark pool which is darkest at the bottom. Let's measure it and see if this is correct. Below I've measured the brightness values of the background in different parts of the image an placed the value on the picture: This confirms what we see when we look at it. But how do we fix it? Well, one thing's for sure: there is nothing we can do to the whole image that will fix the irregular illumination of the field. Whatever we do is going to have to deal with different parts of the image in different ways. This will require a software designed to look for uneven illumination, AKA gradients and correct them. Pixinsight's DBE, Gradient Xterminator, Astro Pixel Processor, Astro Art and others have such tools. But you cannot fix it by black clipping in levels. Olly

I've just had a go at the Ha with three objectives: drag out the outer shell, give the core more attitude, flatten the background. I don't know if I've succeeded... I found it was a devil to flatten and never entirely got there with DBE. I ended up finishing the background sky by hand in Photoshop which is easy if you have empty sky round a central object. This was, as usual for me, a Ps Layers job, one for the background and stars, one for the outer shell and one for the core. I might not process quite as 'hard' as this for real but I thought it would be more useful to the thread to give it some welly! Olly

In your image there are hints of faint secondary features like the 'second broom handle' and outer arms of the broom's brush. Anything faint and teetering on the brink of visibility will benefit from more exposure but you need to know that signal to noise only grows as the square root of the number of exposures, so 'more exposure' is only effective when you have 'a lot more.' Wouldn't you know it!! 😁lly

Mars is red while this image is more like green. This could simply be a colour balance issue, rectified by weighting the three colour channels differently. However, it could possibly be a debayering error. (The Bayer matrix is the set of filters, one per pixel, in a pattern red, green, green, blue over the chip. Each pixel records just one colour. When the software extracts this colour information (debayers it) it needs to know which pixel lies under which colour filter so it can attribute the colours correctly. There are several possible patterns and you need to choose the right one in software for your camera. I'm sure someone on here with the same camera will be able to tell you which pattern to chose. Olly

That's very kind of you but I don't find 'not dithering' to be an issue, really. I've no time for 'rental only' software, either. Olly

There is no need for bias with a CMOS camera and you do need to take darks for flats (AKA flat darks) matched to your flats. (With CCD a master bias can replace a flat dark.) That is just massively black clipped so all the faint signal, whether wanted or not, has been discarded. This is not the way to fight gradients, vignetting, amp glow or light pollution. Here's your histogram: A healthy histogram must have some low flat line to the left of the histogram peak: Olly

My Mesus are pre-Sitech, using the non-ASCOM Stellarcat-Argonavis combination so I don't suppose they will work as yours do. Not the end of the world. I love the simplicity of the old system. Olly

Does this require an ASCOM compatible mount? Olly

I like that. I feel it now has more to say, but we're in the realm of personal preferences here. Olly

Good capture, good processing. This doesn't belong in the 'getting started section!' I think what's particularly successful is that you've left the black point high enough not to have clipped those extra-black parts between the wings of the butterfly. These dust lanes are darker than natural background sky so you need to keep the background high enough to show this, just as you have done. You may already have done this, but any OSC data can benefit from a Photoshop trick: Image-Adjustments-Selective Colour-Reds. Move the top slider left to lower the cyans in red. This usually makes any Ha signal pop. You can use the trick like that or you can save the result and use it as luminance over the original. The blue seems to be restrained in this image but that's probably inevitable with the filter. A consequence is that the Ha regions are more orange-yellow than they would be with more blue. Moving the reds towards magenta might help but you might perfectly well prefer it as it is. Olly

Sorry, my bad. A zero too far! I'll edit it but thanks. Olly

Vlaiv tells you how to do it by the book, which is fine. However, this is how I actually do it: - I don't dither because mine is a dual rig and I take different exposure lengths on each scope. If I could easily dither I would but, quite honestly, it doesn't matter. Slight polar misalignment, reframing after the flip, reframing on different nights, etc, builds in natural dither anyway. - I do shoot bias at 0.0001 0.001 second and I do use them as darks for for flats. If there is a difference, on this camera, between dedicated flat darks and a master bias it will be imperceptible and the tedium of shooting dedicated flat darks is absolutely not worth it. The same applies to my much noisier Atik 11000 as well. I don't know anybody who uses dedicated flat darks with CCD. There is no point since bias does the job, but it is necessary with CMOS. And, yes, you do need flats. Even with my TEC 140, which has a flat, well illuminated field the size of Hampshire, I need them even when there are no bunnies - though there always are. - I've tried using a bias as a dark instead of full length darks with this camera and it works fine if you're at -10C or less but, if you're running warmer than that, it is worth using darks. This is just what I've found with my own 460. Interestingly, and contrary to what one might expect, I find a bias-as-dark and bad pixel map works better than darks on my Atik 11000. This is where experiment leads me to disagree with Vlaiv. When I stopped using darks on the 11000 and used bias and BPM I got significantly cleaner stacks and with a lot less trouble. Plenty of other imagers have stopped using full length darks as well, finding they get better real world results with bias and bad pixel map. Theory and practice do not always agree. - Atik software is free to download from their website. I'm using the older Artemis Capture, which I love, and am rather dreading having to learn my way around the new software. I had some advice from Ian King many years ago: If you're having trouble with a product, run it in its own software. That's the argument in favour. However, the old Artemis won't communicate with PHD so, to dither, you'd need a capture software which did. That's the argument against. (I don't know where the new Atik software stands on this. Anybody?) - Finally a 460 quirk (on my example, at least.) I get clean stacks with good signal. However, when I begin stretching process I find that the background sky values remain very low. If I use a conventional log stretch in Ps Curves I'll find the brighter signal is reaching the upper limit before the background sky has come up to the kind of value I like (which is around 23 in Photoshop.) In the end I usually have to settle for a darker background than I'd really like. I can't explain this and it might not happen at a site with LP. My skies are very dark. Essentially it's an easy camera to use and does the business. Have fun! Olly PS Anyone interested in a 460 should know that SGL member Gorann has an unused one for sale.

I agree with this. The key difference between the two is that Photoshop is a work of genius in communication. Nobody could accuse PI of that! Ps, from its inception, set out to provide a visual interface between new-generation mathematical digital types and old-school printers, graphic artists and photographers used to working in analogue environments. Beneath the surface both are purely mathematical but Ps has an interface which creates what are, in effect, metaphors which will communicate with visual people. We are making pictures, so a pictorial interface makes a lot of sense to me! Olly

...exactly why I like Photoshop. Olly

One thing I'd try would be a dose of SCNR Green in PI. It's adjustable with a slider and might do well on this image. Olly

That's pretty good but I get the feeling it could go significantly further in post processing. I don't know what the 'EZ' processing scripts are but I don't like the sound of anything which suggests that 'one size fits all.' In American English EZ says 'easy' and that doesn't exist in AP. For me, post processing is all about looking at the image, taking a small step, and looking at it again - very carefully. When I look at this image very carefully I'm sure it has even more to give. Olly Edit: I didn't spot this first time around but this thread is in the wrong section. Mods?

Does anybody else on here think that telescope manufacturers who sell kit-form telescopes should actually state that this is what they are selling? Olly

This is a great sensor. Look at all that signal! Olly

The plus side is that, unlike motor racing or flying an aeroplane, the running costs are low! Olly

I'm very happy with the Baaders. I'd go upmarket for Astrodon or Chroma for narrowband but not for LRGB. (Unless I were using an ustra-fast optical system, which I'm very unlikely to do!) Olly