ollypenrice

Going back a few steps in the conversation I keep things simple by capturing onto two PCs. I know I'd tie myself in knots if I tried to run both cameras on one PC and I have more screen space which is good. How precise your second scope alignment needs to be depends of the relative FOVs of the two rigs. The original dual rig had identical kit on both sides so it had to be close to perfect. The solution came, at staggering expense, in the form of a second hand Cassady T-GAD alignment system but FLO now do a good alternative. If one FOV is much larger than the other you might get away without anything. (The T-GAD has no difficulty holding two TEC140s still at a highest resolution of 0.9"PP.) I don't dither but I do take a lot of data and the noise patterns of the two cameras are not the same, which I think helps. (One guy on the French forum insisted that 4 + 4 hours from two cameras gave the noise of a 4 hour capture while 8 hours in a single camera gave the square root of that amount of noise. I don't think he's correct.) Is a two mount solution easier? Sara automates her capture while I don't. In her case I can see that it might be easier but in my case the dual rig works like a charm. Olly

Aha, I was baffled when one camera lost its long-time column defect. Maybe I nutted it while fumbling around in the dark! Olly

This is certainly true. For what it's worth I prepare images for print by adjusting the curve along these lines: The idea is to lift the lower brightnesses so that faint detail will not be compressed into oblivion. I find print has an effect rather like black clipping, but since it can also white clip I'm careful to hold down the brightest parts. The good news is that print resolution will not capture the finest pixel structures and these include noise. Tony's list of things to get right at capture is certainly a sobering one! I'm not suggesting for one second that it isn't both expensive and sometimes exasperating and certainly I think that those who do it while fighting bad weather and LP are downright heroic. As for those who have to drive their kit out to dark sites every time, well, they are beyond heroic. But, while the list is long, there is no one thing on it which you could really call difficult. When everything works ( ) an experienced observer, new to imaging, can get to the successful capture stage in a couple of nights. I see this fairly regularly here. However, I have never seen anyone teach themselves to process successfully in three days. Anyway this is an aside to the main point of the thread. Apologies. Olly

It might be worth citing Tony Hallas, here, too. He advocates dither, bias as dark and that the dither be of at least 12 pixels to combat DSLR 'colour mottle.' Olly

Ouch, I feel tempted to don a tin helmet before peeping above this parapet! However, some jottings: - I feel it would be, almost by definition, a shame to bring earthly parochialism into our study and enjoyment of the vastness of space, so magazine sections 'From Britain' and 'From Elsewhere' would sound a very wrong note for me. (I'm tempted to add, 'Especially at the moment.') - A magazine article or 'occasional series' on the trials and tribulations of a beginner or LP dweller strikes me as interesting. It might include suggestions from an experienced imager at the end. (This is very much the astro forum format, after all.) - Magazines are physically quite small and print resolution is lower than screen resolution so many of the advantages of extremely long exposure and very expensive equipment are lost in print. The print playing field, if you like, is much more level than the pitiless screen playing field with its potential for zooming in to full size and (hiss!!!) pixel peeping. - Data acquisition is a learnable mechanical process with a clear and not terribly high ceiling. Processing is far more complicated, open to more varied approaches and limitless in terms of potential for improvement. I know not everyone agrees with me on this but I don't really care where the data comes from. My own joy lies in interacting with it (and so with the objects it contains) at the processing stage. (Great artists used to mix their own paints from pigments etc. Now they mostly buy their paint. Is this important? OK, that's a tenuous analogy. ) - Having been addicted to sporting competition on motorized and non-motorized vehicles for more than half my life I absolutely love the fact that astrophotography is not a competion! - I hope Keith isn't going to turf me out of the pages of his excellent magazine because I... well, you know, sort of... live in France. Olly

Nice. How much signal did you find in RGB? Olly

Very fine. Olly

I never go out and battle the moonlight but perhaps I should! Olly

I find it depends on temperature with mine. A master bias-as-dark works fine when I can get down to -15 or so but when I can't, in summer, it does need darks. Olly

Although it covers all aspects of making a Dob, this book is considered a bible: https://www.willbell.com/tm/dobtel.htm If you decided not to make it yourself you're only a stone's throw from David Lukehurst. https://www.dobsonians.co.uk/ The key tool in Dob making is probably a router which will allow you to cut good circles for the Dec bearing. Olly

Flats you need. No question. Darks, if you are dithering, maybe not. When you find the community disagrees it is best to experiment for yourself. However, using imaging time for taking darks will never make a profit. Olly

It can be had in the Baader 8nm filter because that's what I have, but narrower bandpasses are certainly better. I'm sure a dark sky is important, though.

Flawless, Rodd. Olly

Nicely done indeed. Because the main cluster is bright, folks often don't take enough time to do justice to the nebulosity. Your 12 hours here are showing what happens when the target gets the time it deserves. Olly

Does it have to be in PI? In Ps I'd just do two stretches, one for the bulk of the image and one very soft one for the saturated regions and their immediate surroundings. Then I'd blend them using layer masking. Alternatively you could experiment with home brewed curves. Essentially you'd bring the curve to a straight line quite low down as below. This would also be the kind of soft stretch I'd use for one of the layers (the one in which we are trying not to further blow the cores.) I agree with Vlaiv that blown luminance cores are a fact of life but in post processing this can be fixed. Have you considered using your RGB as a set of short exposures for blending? This often works very well so I often do it for cores. You can convert them to greyscale and treat them as short luminance exposures. Olly

At least I'll be glad to hear that it isn't just me! I shoot more data than most members, doing this for a living and running up to three rigs per night, so if it's a random problem it's likely to hit me more often than most. With some dual rigs operating remotely, though, some other members are now shooting more data than I do. I always follow this issue with interest because there must be an explanation for it. Olly

No bother at all. I'll PM you. Olly

Me neither! Gimme layers! ly

What a great idea for a composition and that snake of dust just hanging there really makes it! I have 24x30 minutes of Squid OIII data which I'd be more than happy to send you if you fancy a play. 24x30 might sound like a lot but in fact it's pretty thin. Still, just PM me if you'd like it. Olly

Mount first, yes, but I'd argue for camera second and optics third. However, I think I'd go for the Esprit myself. Olly

That was a good stretch, really emphasizing the propeller feature. Olly

This isn't my field but Vlaiv and Dave seem to have a handle on it. I do sometimes see atypical background artifacts in Ha data and put it down to the fact that I'm often stretching my Ha data (especially for galaxies) way, way harder than I would stretch anything else. The endgame of galaxy Ha is, after all, often little more than the addition strings of low resolution 'blobs' to spiral arms. In the way that I combine the Ha only the brightest signal will end up in the image anyway so low level artifacts will be excluded, as Rodd says early on. I don't think we really quantify the severity of our stretches. I certainly don't do so. It might be interesting to know the extent to which a background sky value, for instance, has been stretched. Obviously it will be far, far higher in NB than broadband. Olly

A lot depends on whether you aim to do broadband or narrowband imaging. NB imaging asks far less of the optics because you are working in nearly monochromatic light, so good colour correction is not needed. This really involves a mono camera. If you are shooting in broadband, whether one shot colour or mono and LRGB, the Esprit will give you perceptibly smaller, tighter stars, particularly in the case of the hot blue ones which will bloat a little in the ED80. It's hard to quantify such improvements but put it this way; offer me either an Esprit with a DSLR in it or an ED80 with a cooled mono camera and filters and I would take the ED80 any day. No hesitation at all. The cooled mono could be a less expensive CMOS or more expensive CCD. My rule of thumb regarding priorities goes mount-camera-optics. Olly

Sensational result, Peter. The best I've seen. (I've seen plenty where I was left wondering what I was supposed to be looking at!) Your PN images are always terrific but this is at an even higher level. Olly Edit: The 6 inch refractor strikes again! Yesssssss.......

Couldn't you fix up a projection screen? Olly