ollypenrice

Hi Anne. I first tried Straton but it made a mess, so I made a copy layer, used Noel's Actions to select brighter stars on the top, expanded and feathered, erased them, then ran the dust and scratches filter on the bottom layer. This meant I could see the effect of Dust and Scratches in real time. It wouldn't have been satisfactory as a de-starred standalone image but I wasn't wanting that anyway. When I then put the original on top in Blend Mode Lighten I could let the stars back in at an opacity I liked. They were a bit spikey-looking so I gave them a very slight Gaussian blur. I suspect that with diff spikes your only option would be the clone stamp. Olly

By the way, Monique spotted a human face in this one. It's in profile, facing to the left. Find the closed eye above the Eagle's claw and you'll spot it. We called it 'The bearded face.' It would make a companion for the WItch Head. 😁lly

This is a reprocess of old data using a star reduction technique I hadn't encountered at the time I did the original. Obviously we're in the thick of the Milky Way here and holding down the stars to let the nebulae do the talking is tricky. The image is HaLRGB from the Tak FSQ106N and full frame Atik 11000 (still my favourite camera...) Both nebulae were enhanced by applying higher resolution data from the TEC140. All I did was remove the stars entirely from a copy and then replace them with the originals at only partial opacity in blend mode lighten. Very easy indeed and, for the first time, I'm happy with this one. Mount, as ever, was a Mesu 200. Olly

Don't beat yourself up, these things are a nightmare. I think the origin of the four obvious halos is 51 Cygni because the repeat reflections are all equally spaced. No Nobel prize for getting that far!! I may be wrong but I get the feeling that we are seeing a lot of posts like yours since the new CMOS astro cameras appeared. I don't think internal reflections were so prevalent with CCD though they did happen. The glass in the system includes corrector plate, primary, secondary, filter, chip window and (I think,) chip micro-lenses. The trouble is that it will probably be an interaction between some of these surfaces, but which? I wish I knew. Olly

I agree with Billy. It's best to do darks off the rig with the camera's window cover in place. Many have screw fit metal covers for this purpose. The tiniest light ingress will invalidate the darks. I also do try to do flats in the dark, even on refractors which are sealed. When I can't I put a dark drape over the rig while shootng them. I think you'll struggle to get food reflector flats in the light. Olly

The situation regarding dark flats is different in the case of CCD chips and CMOS chips. A CCD camera can have its flats accurately calibrated by subtracting a master bias because this will, to all intents and purposes, be the same as a short dark exposure to match the flats exposure. WIth CMOS chips a flat dark must be shot at the same settings as the flats in question. With regard to an uncooled DSLR camera (especially in warm Malaysia!) I really don't know what you should do. Personally I would experiment. Try making a stack of flats uncalibrated and then use the same set with dark flats and see if there is any difference in the final deep sky image when you try one then the other. Sometimes I find dark flats necessary to avoid over-correction and sometimes I find I can't tell the difference. In theory you should certainly take them but when you have no control over chip temperature I think only experiment will find the best answer. Olly

First or second for me. There really isn't any 'background' in this frame anyway. Good stuff, Carole. Olly

Per used a 10 Micron with quasi-absolute encoder guiding and a sky model. I'm sure about this because it was in our robotic shed which he designed! He didn't guide on a star but there was a feedback loop between his mount encoders and the drives and the sky model corrected for changes in atmospheric refraction due to altitude. I have a pretty good idea of what he would have said about the DFO website... Olly

No, this war has been rumbling on for at least two hundred years... Just one word of caution to the OP: when you read apo refractor nuts (which might include me) banging on about the quality of the image, they are generally talking about posh refractors. Expensive ones. I have two of those which cost, between them... well, never mind... As a general rule a budget reflector will beat a budget refractor. 😁lly

Rob, the mod is to the mount, not the camera. However, it seems that a Canon 200D in a 130P would be imaging at 1.17 arcsecs per pixel if I have that right. This would require a periodic error of 0.6 arcseconds over the duration of the sub. Is there is any experienced imager on this forum who would believe that? Such a claim is absurd. This mount modifier should stop talking about this scope or that and simply state the periodic error in arcseconds which he is prepared to guarantee. Bear in mind, Lucas Mesu claims 4 arcseconds peak to peak for his stunning 200 Mount. And let's have no talk of round stars! You'll get round stars as long as your tracking errors in RA and Dec are about the same but you'll still have lost resolution. On another matter, if we look at the OP's very promising M42 we see that it is heavily black clipped: The histogram pedestal is jammed up against the left hand edge of the frame meaning that all the faint signal to its left has been discarded. Don't throw away what you catch while out under the stars! A healthy histogram looks like this: Be careful not to bring in the black point too far. Make sure you leave a bit of flat line to the left before the histogram peak begins to rise. Olly Edit: a standalone guider can be had but, honestly, even a tiny laptop is a great help when imaging. Don't think about the largest scope you can get away with. Think first about the tracking accuracy you can achieve. Guided this might be between 0.5 and 1." Double that and that is your finest possible imaging resolution. There is nothing to be gained from a longer focal length and all you will do is lose field of view.

An ordinary entry-level guided mount will out perform pretty well any unguided one if we consider encoder-guided mounts to be guided. As SamAndrew says above, guiding will vastly out-perform tuning. Olly

Looks good to me. Nice streamers appearing in the dust. If you want to get clever you could start with the original and make a copy. De-star the copy and then give it the kinked curve treatment, only harder. It'll probably then need a de-noise. Finally apply this as a top layer over the original in blend mode lighten. If you do this, the top layer's dark background sky will not appear in the blend, and the stars will be entirely unaffected. The de-noise will only be present in the highly stretched nebulosity where it's needed. Olly

Fabulous image, Pieter. Astrophotography at its best. Sorry about the accident! Olly

You might want to read this thread: https://stargazerslounge.com/topic/350628-dark-frame-experience/ I would use the WO since nothing is more portable than a small refractor and it will travel well without costing you time collimating in the field. An alternative line of attack would be to keep the Star Adventurer and buy a cooled OSC CMOS camera for use with a fast camera lens like the Samyang 135. You'd need to be sure an adapter was available but FLO will sort you out there. The key advantage would be speed. You'd have fast optics and a fast camera with low read noise, so it will work well with short sub exposures. This makes tracking less of an issue, as does the short focal length. There are lots of great widefield targets out there... Olly

The simplest way is to use Curves. This is in Ps but many graphics packages have it. First put a fixing point on the curve at at the level of the darkest parts of background sky. That's the second highest point on the curve below. Put a fixing point beneath it. Next, raise the curve just above the background (the third highest point on the curve) and, finally, restore the curve at the top as far as possible without putting a negative bend into it. You're just trying to hold down the stars. This was a qickie but with careful attention to the shape of the curve you can concentrate the change only onto the faint nebulosity. You could also try a similar but slighter adjustment to the blue channel only but you're no longer being so honest with the data. The pinning of the lower part of the curve has the same effect as masking out the background sky. There are plenty of masking techniques as well but the kinky curve trick is the easiest in my view. Essentially 2 hours is not long if you're going for faint signal. Olly

When people say something is 'just a theory,' I think that, nine times out of ten, they mean, 'That is just an hypothesis,' and fail to understand the difference. The same people, ironically, are full of assumptions which they hold as certainties when, in fact, they are 'just theories.' 😁 They will hold it absurd, for example, for time to begin. In the same irony it is they, and not the scientists, who believe in absolute reality. Are you not in danger of putting words into Andrew's mouth, here? He never said or implied that humans certainly have the intelligence to understand where the universe came from. I rather doubt that he would say such a thing. Olly

Since the BB runs time backwards to within a vanishingly small time before something which looks like 'a beginning' it seems to me to be natural to speculate that, after all, the 'universe' we're looking at here may not be all that there is. I think it would be obtuse not to speculate along these lines but it would also be obtuse not to realize that we are only speculating. However, if we could come up with an hypothesis of 'other universes' which predicted observable indicators present in the one we can observe then we could look for them and we'd be doing science again. The speculative hypothesis has been the start of many scientific theories. What would be profoundly unscientific would be to say, 'We will never have have any way of constructing a substantial theory of other universes.' I'm not accusing you of saying this, by the way, I'm just following the idea. Olly

I think I need to read about fields in general... It's a very strange notion for me, though clearly a powerful one. I see Carlo Rovelli has written a book about time. That's on my list as well. Olly

Of course, you're a long way ahead of me but I do know 'An Introduction to Modern Cosmology' as a one-time course textbook. But I think, as many do, that the notion of creation 'ex nihilo' runs against the grain. That's not to say it's wrong and, as I never tire of thinking, nature has no obligation to seem reasonable to us. We are a product of our immediate circumstances, not of all the circumstances which may be. But I do think the question, 'What happened before the BB' is worthy of consideration and additional dimensions can resolve it - very vaguely. Why would we assume that we can perceive all that there is? I'm instinctively highly suspicious of string theory, though I have not the slightest competence in its mathematics. My doubts arise from my readings in the history of science, encouraged by Lee Smolin's 'The Trouble WiIh Physics.' One of our regular guests is a string theorist by profession and said that he had considerable respect for Smolin's objections. But the detail is far beyond me. Olly

Words matter. Within the Big Bang theory the phrase 'before the big bang' is meaningless because the theory has it that the dimensions of space and time as we observe them began at the big bang. 'Before' is a term which is only meaningful as a term within that time dimension so it cannot be used outside that dimension. 'Before the BB' is as meaningless as 'On the Matterhorn in London.' The Matterhorn is not in London so the phrase is meaningless. However, nothing in the BB theory stipulates that are no other dimensions in existence. Dimensions outside our observed space and time dimensions can exist and from those dimensions our BB universe could have been born. I think it safer to talk about outside the big bang universe rather than before the big bang because the term before should not be applied to dimensions other than the BB's time dimension. It's already bad enough without having two different concepts of 'before' sharing the same word! The same can be said for space. The space dimension(s) of the BB universe exist only in the BB universe but those dimensions may not be the only ones. It's also worth remembering that the idea of past, present and future cannot be regarded as fact. They are themselves part of a theory of time and may be illusions. Olly

Either way is interesting. Olly

A friend sent me a link to this article about a woman injured by a meteorite. Curiously, I've never heard the story before and, being only one at the time, I have no direct recollection of it! I've encountered articles about a car hit by a meteorite dozens of times, which only goes to show what our priorities are!! 😁 https://en.wikipedia.org/wiki/Sylacauga_(meteorite) Olly

Good to know. Maybe they should check all scopes before sending them on, though, since the problem is widespread. Taks are extremely expensive, after all. Olly

One thing to check: does a single sub show the same distortion? It's just possible that the stack might be accumulating field rotation from polar misalignment if the guide star was closely on-axis. Unfortunately there have been plenty of problem FSQs reported on the forums in the last few years and I've seen three here. Olly