ollypenrice

Quite apart from sampling theory, there is the matter of exposure time to consider. Even assuming you are not over-sampling (by shooting at less than about an arcsecond per pixel) you will need a lot more integration time to produce an image which looks good at 100% than at a reduced size. As Vlaiv said, if you are over-sampling the image will never hold up to scrutiny at full size (when one camera pixel is given one screen pixel.) But even if you are under-sampling it will take you longer to get a signal to noise ratio that will support full size scrutiny than one to be viewed at reduced size. In general I try to reach an S/N level which will support full size and sometimes, when imaging small targets, it's essential to do so to get the target to a respectable screen size. However, in shooting a widefield mosaic, for instance, you might feel that there was no need to make the final image of several panels hold up to full size. You might prefer to reduce the exposure per panel, resample the panels downwards and still end up with a very large picture. This might take the panels down from 10 hours exposure to 5 with negligible loss once shown at considerably reduced size. It's part of the planning, therefore, to decide in advance what your target presentation size will be. Of course, if you want to play it safe you should follow the advice of SGL member Maurice Toet who, when asked how long he intends to expose for, replies, 'As long as it takes!' Olly

Personally, without stabilization, I prefer to come down to 8x for a steadier image and I find 42mm gives a nice compact binocular and a bright, crisp image. Olly

Spot on. Tip top. Olly

So will I. Olly

You need an accurate, motorized mount for this job. That's my honest answer. Olly

You can use masks as one way of separating dust from background. Carole did an admirably clear video on a technique of mine which makes use of the equalize filter. However, my first step in lifting faint glows out of the background uses a simple kink in Curves. Put the cursor on some pure background sky and alt-click to put a point on the line at this brightness. Apply a fixing point to the line below that. Now put a third point on the line just above the first and lift it very slightly using the input-output values on the curves window. Finally return the line to straight so as to keep the upper brightnesses almost as they were. This will hold the pure background where it is and slightly brighten the faintest glows above the background while having little effect elsewhere. If your background sky is uneven be sure to pin it at a point where it is at its brightest or you'll introduce a gradient. Here I'm trying to pull out the Owl's faint OIII halo. Background was pinned at 22. Fixing point placed at 12. It's like trying to get a lever between two objects so you can prize them apart. Once you have them separated just a bit to start with there are lots of other techniques which are more subtle. Olly

I'm inclined to agree. Olly

There are plenty of videos online but some of them are absolute rubbish and are put out by people who haven't the slightest idea of what they are doing. It is usually easy to spot these. When you hear phrases like, 'I usually just play about with xxxxx till it looks right,' stop watching. Any competent image processor knows what they are doing with each tool and will tell you what it does and how it affects the image. They will not simply present a series of clicks and draggings. (Draggings is a new word! 🤣) Expert names to trust: Jerry Lodigruss, Robert Gendler, Adam Block, Warren Keller, Tony Hallas, R Jay GaBany. There are many others but do make the most of Steve's book. It is very sound. One thing to start doing straight away is to enhance your ability to make a critique of an image. When we start we are likely to be impressed by all images. Greater discernment comes with experience. Is the sky a neutral dark grey but not jet black? Is there an overall colour caste which shouldn't be there? Green, magenta, red, whatever? Is there any visible noise reduction? There shouldn't be. Is the image too noisy? A little grain is good, more than a little is not. Are the stars small, tight and credible in colour? Are any parts of the image saturated, burned to white? There are so many things to appreciate that it does take time to become a good observer of images. Your image seems a little red-dominated and you might be able to rescue the Trapezium by making a much softer stretch and blending it like this: http://www.astropix.com/html/j_digit/laymask.html Olly

To be perfectly honest I was profoundly underwhelmed when I went from my early 8 bit Ps 7 to my present 16 bit Ps CS3. I was expecting to find a very obvious difference but simply didn't. I never did a careful comparison but nothing jumped out at me from the screen. I'm not convinced that this is a big deal in practice and will continue to use my bought-and-paid for CS3 until some Windows update prevents it from working. Then I'll go off in a sulk and not come back! 😁lly

While I'm interested in astronomy history, I'm also a little bemused as to why someone with such a specific and highly detailed question should be posting it here and not in more academic circles. But perhaps you have already done so? Please, this is not a criticism but it may have something in common with Marvin Jenkins' reaction. I guess it would help to know where you're coming from. Olly

What a pain. I'm even sorrier for the owner than I am for the rest of us! I think I'll wait for a miracle recovery for a while before deciding on whether or not to reload my pictures. Our internet isn't fast so that would be a tedious job. Will the day of reliable IT ever dawn? Olly

A lot depends on the mass of the slab but I have the following observatories, all built on single concrete slabs carrying the walls and to which piers are directly bolted using threaded bar bonded into the slab. - 4 scope robotic shed, 3M x 4M, 6 tonne base. - Single mount dual scope imaging observatory. Base mass roughly 3 tonnes. - Single scope robotic shed. Base mass 1.5 tonnes. These all work perfectly and show no need whatever for the isolation of the pier slab. - Single scope imaging observatory built on two-part concrete slab. I can't remember why I laid this slab in two halves but it was a silly idea! The shed works but heavy-footed moving about inside it does show very briefly on the guide trace. It simply means that I have to be careful when I move, at least when imaging at fine pixel scales. A single casting of the slab would have worked fine. Conclusion: I would expect a former garage base to work perfectly well with a pier attached to it. Peter Drew invented a cheap and easy pier known as the 'Todmorden Pier.' https://www.google.com/search?q=todmorden+pier&rlz=1C1CHBF_enFR821FR821&tbm=isch&source=iu&ictx=1&fir=a71unkkhOJN1kM%3A%2CWl7whdD2DAJ3LM%2C_&vet=1&usg=AI4_-kSIKSVnn4aUcVIZO2xahGyDNMbp0w&sa=X&ved=2ahUKEwj639qcjNjnAhXo4IUKHXpZBEEQ9QEwAXoECAcQBg#imgrc=a71unkkhOJN1kM: I came up with a slightly harder-work concrete pier alternative using pre-cast concrete cylinders placed over vertical rebar epoxy-bonded into the slab and then rubble-and-concrete filled. We've made two of these and they work well. There's a picture on this thread. Olly

I rather doubt it because PI won't let you use brushes to remove part of a layer, so far as I know. I dare say it could be done in freeware like GIMP. Olly

^^ 8x42 for me, too, hand held. This was a change from my previous 10x50. Olly

Always edge crop anything you take into Registar. Vital. You open two images in Registar and register, let's say, B to fit A. B will then be reorientated and resized to fit A but it will not be adjusted in any way to 'match' B in terms of levels, colour balance, contrast etc. Only if you activate Calibrate will it be adjusted in order to make a seamless blend with A. If working with linear data you have a fighting chance that the two images will now match well enough for a seamless blend via Registar's Combine Images command. But even with linear data there may be a line visible. Don't panic! Read on... Let's say images A and B are still linear and framed to make a mosaic, A on the left, B on the right. Ask Registar to register and calibrate B and then combine them. Save the combined image but also save the registered calibrated version of B on its own. You may need this as a 'patch' panel. In Photoshop stretch the combined image not all the way but hard enough to reveal any defects in the calibration but record your stretching as an action. There are two potential sources of a visible line, the right hand edge of A or the left hand edge of B. Let's say we can see a line at the right hand edge of A (so visible on panel B of the combined.) This is sooo easy to fix... Open the saved Registered Calibrated B and run your recorded stretching action on it. Now it will be all but identical to the stretched combined image. Paste it onto the stretched combined and move it into the right place with the move tool. Use a feathered eraser to take off all of this top patch panel except the bit covering the line or joint defect. Flatten and congratulate yourself! If the visible line is from the left hand edge of B it is on the original A panel, which you already have. Run your recorded stretch and patch in the same way. I don't know any Registar tutorials but in this post and the one above I think I've set down all the methods I've evolved in using it. PM me for clarification if necessary. I couldn't function without Registar. Olly

Scrumptious. I'm a great fan of blending higher resolution 'areas of interest' into widefield images of lower resolution. I do this using Registar followed by Photoshop. Usually I'm working with processed data because I already have it. Starting at the linear stage all round is a luxury. This is what I do: 1) Open Hi Res and Wide in Ps and try to get the Hi Res looking as if it could be blended in. (Adjustments to levels, colour balance, etc., just by eye. 2) Take both into Registar and Register Hi Res to Wide. Then Calibrate Hi Res to Wide. Then Crop and Pad Hi Res to wide and save it. I don't combine them in Registar. The terms in red are standard functions in Registar, one click for each. 3) Import the Hi Res output from Registar into Ps and paste it as a top layer onto Wide. It will be perfectly aligned with a black 'padding' border round it which I discard by using Colour Select set to zero fuzziness to locate it and Delete to discard it. 4) Now the fun begins. Where there is a big difference in resolution (as there usually is in my case) I want to merge the Hi Res in slowly so that its outer edges will be invisible and its contribution to the bottom layer will increase towards its centre. I use a feathered eraser to let it in slowly. Adjustments to brightness can be done using Dodge and Burn brushes and individual channels can be given this treatment to get a seamless blend. Finally the percentage opacity of the top Hi Res layer is something I judge by eye based on looking seamless and having the lowest noise (though a big downsizing of the Hi Res usually eliminates noise completely in my case. As you can see, this is a hands on, 'artisitic,' process and not a uniquely digital one. I love doing it but some would hate it. Some examples: https://www.astrobin.com/cqd5z8/0/?nc=user https://www.astrobin.com/335042/?image_list_page=2&nc=&nce= https://www.astrobin.com/321869/?image_list_page=2&nc=&nce= If the differences in resolution are not great you might just get away with combining the linear sets with hard edges but I wouldn't bank on it. I suspect it will always be an arty process! Olly PS It makes perfect sense to use all the data you have. Running an imaging guest house means I often have multiple datasets and in my view it makes sense to combine them as well as to to make an image from the new data. (Naturally guests want to do that because it's their primary image but why not also make a stack of stacks?)

A reflector is, in principle, best guided with an OAG. Are you sure you have the backfocus? And, if using a coma corrector, can you maintain the right chip distance from it? Olly

I think that's a cracking M27 and I very much like the tenuous outer glow just as it is. The fact that you can get it to show more strongly doesn't mean that you have to. Yours feels very true to the object when I look at it. Given that the outer shell contains no fine details it can be stretched and noise reduced considerably harder than you have done here, I think, but it would be important only to add the shell and not the stars from any such hyperstretch. Something I don't think anyone has mentioned on here is the Ps option to add noise. Why would you add noise? Well, very occasionally I do. Anything extremely faint may need NR to the level of looking oily, which we all hate, but the judicious addition of a touch of noise can make it look natural again. Just doing less NR in the first place is not equivalent because it may be large scale blotchiness which the NR is killing and small scale noise which is added afterwards. Olly

I wouldn't attempt to hand hold 15x other than with image stabilization. In the birding world it is almost unheard of to hand hold at more than 10x and, in my view, with very good reason. Before anyone decides that they really can hand hold at 15x they should perform a self test by having a pair of 10x binos handy as well. Find some text at the limit of what is readable at 15x and then try the 10x on the same text. Most poeple, though I don't insist that it will be all, will not read more easily at 15x, showing that the higher resolution is lost to the jitters. Olly

Remember that you don't have to have the focuser the 'right way up.' If it helps to do so you can rotate the scope till the focuser is on the top. You can also add a weight to the front of the bar if it's rear end heavy. Olly

You're thinking very much along the right lines with mount first. I'd keep your 1 to 4 as it is. Master the mount and the business of guiding (which you are unlikely to find difficult if you're a techie) and get focus right then learn the rudiments of image calibration, stacking and post-processing. The only thing I'd add is that you don't need a scope at all, you could try camera lens imaging. There are some outstanding Samyang lenses winning friends on here or you could look for an old prime lens to fit your camera. You don't need autofocus. Oh, add a Bahtinov mask to your shopping list. What about software? DSS will get you started for free on stacking and calibrating but I greatly prefer AstroArt which is moderately priced. You'll then be faced with the Photoshop-Pixinsight dilemma. I use both but am really a Photoshop diehard. Or there's Astro Pixel Processor, Gimp, etc. Olly

This looks massively black clipped. You have a jet black and uniform background sky and little faint data. This is where you need to be careful: Healthy: Black clipped: You must always have some flat line to the left of the rising histogram peak or you'll be discarding precious data. It is tempting to black clip in order to get rid of gradients but resist this temptation. Olly

Very good. What makes this tricky is the need to get the background sky just right - as you have done. More data might allow you to pull out the blues in the tidally distorted component of 'The Eyes.' Olly

You can't do Cygnus on its own. Too many structures head off into Cepheus... 👹lly

Because Alt Az is nicer for visual and EQ is better for long exposure astrophotography. Olly