ollypenrice

Yes, I dread moving away from Artemis Capture (which I call Artemis Rapture ) but Atik have moved away from it themselves. I gather their new software isn't even written on papyrus. I ask you! Olly

Pixinsight developers disapprove of this and call it 'painting.' I find this a ridiculous assertion and do what you're doing here in a mixture of Registar and Photoshop. It's an excellent technique. Power to your elbow. Olly

I don't think off axis performance is as important in binoculars as in a scope because, in a scope, you will move your eye or even your head to peer into the field stop. With hand held bins you'll just move the bins with your head, keeping your subject central. I tried some Victories belonging to a guest and found them absolutely stunning. Olly

Scope arrived today, seemingly in good health and in a dent-free box delivered by UPS who are always, and by far, the best around here. I had a to-do when fitting the top dovetail because the longer screws in the bag didn't fit in the scope. Too big. But... it turns out the accessory holes in the front of the tube are fractionally bigger than those in the rear of the tube so they need fractionally different bolts. Well why not? Why miss out on a chance to add confusion? The three-column pier raiser in Avalon Sexy Red will have to go because, in the Polaris position, the roof already touches the top of the rig, even without camera. I may have room for a lower height-raiser once we see the front loaded with camera and dewshield. We want it as high as possible because we can and do keep shooting down to the horizon on some targets, here, but the observatory wall will cut us off. Now we need a camera, a PC and the usual pasta-fest of cables... Olly

Scope arrived tod

Few amateurs use derotators but Alt-Az with derotator has been the professionals' choice for some time. These are, though, two different worlds. Olly

There is no need for close alignment between guidescope and main scope. For years I've been using guidescopes bolted down hard onto main scopes with no means of aligning them. I prefer that to using adjustable guide rings because what really matters is the stiffness of the connection between the scopes. Remember that adjustable guidescope rings were not invented to allow you to align guidescope to main scope: they were invented for precisely the opposite reason, which was to let you set your guidescope off axis to find a guide star in the days when insensitive guide cameras struggled to find them. That problem no longer exists. If you have a literally perfect polar alignment (unlikely) you will see no difference whatever between an aligned and a not-aligned guidescope. In the real world what you will see is that polar misalignment will cause your imaging camera pictures to rotate around the guidestar, wherever that guidestar is. It may or may not be in the frame of the main image, depending on where your guidescope is pointing. I suppose that, with a truly awful polar alignemnt, you'd be best off with the guidestar in the middle of the main image. In reality, with a decent but imperfect polar alignment it really doesn't matter if your guidestar is off axis. The longer your subs the more it matters but I often use 30 minute subs with a randomly aligned guidescope and a decent but not obsessive polar alignment. I can't see any field rotation in half hour subs and five minute subs would obviously give six times less - so this is a non-problem. Olly

This is all new to me so I don't know these systems. Can you eloborate a bit? Olly

Great information. Thanks. I guess the guide cam will do for collimation but I also have Lodestars. I rather hope it's like your first one! Olly

Some things to clarify: 1) You will need to stretch the image to see fainter nebulosity. Are you familiar with stretching linear data? Some software will give you an automatic 'preview stretch' but usually you have to initiate a stretch yourself. If you capture into a PC you can use your capture software to do this. In their original linear form most astro-images look like stars on a very black background with little else showing. 2) You'll need to remove the LP gradient or orange washout. With modern software this is remarkably easy. Pixinsight's Dynamic Background Extraction lets you tell the software what should be neutral background sky (dark grey) in your capture and then, when applied, the algorithm re-balances the colour and lets the underlying details emerge. Alternatives to Pixinsight include Gradient Xterminator (Photoshop plug-in), Astro Pixel Processor, Astro-Art, Startools and more. You'll need a post processing software anyway so be sure to choose one with a good gradient remover. Olly

Doh! 🤣 If you move on to ultra-tight doubles which you're struggling to split, you might be able to split them in an Ha filter and use that as luminance. Olly

Thanks. Yes, the camera will be the 2600MC. I found that the 11 wouldn't fit in the observatory without the possibility of roof collision and we have a strict 'no collision possible' policy. If it can happen, one day it will happen! I need to go and do some homework on how to collimate and tune out tilt in case we have it. It's a relief to hear you say it's not too difficult! What have you found out about sub lengths, Goran? Olly

It might be worth doing a G2V calibration in order to get the correct exposure weighting for your filters. I'd have thought it would be preferable find your colour by this natural method than by doing it artificially. It's odd that you found so little colour in Albireo. What post processing software do you use? Olly Edit: maybe also consider dithering, not to reduce noise but to move the Bayer Matrix around under the star to ensure proper sampling of colour.

We'll happily publish our final choices once they are working and stable. We don't want to pump out bad information or guesswork ahead of experience, though. Olly

I think it is. The resolution, from memory, will be about 1.8 arcsecs per pixel, so fairly fine (compared with the Tak/Atik 11000 at 3.5"PP) and sub lengths remain to be tested but people seem to be using 3 to 5 minutes. Will an unguided Avalon deliver a PE of less than 0.9 arcseconds over that time? I very much doubt it, though you might conceivably get round stars if RA and Dec errors are of comparable amplitude. Planets? You mean those little round things just in front of the end of the telescope? 😁 No, they're too difficult and Damian Peach is too good at them! Olly

The signpost says Damascus... 😁lly

I've always been doubtful about the practicality of ultra-fast optics and an advocate of mono over OSC. So... I'm having a change and participating in an OSC project at F2 with a CMOS camera! (Wot no CCD???) On top of that, I've always done everything manually: framing, focus, meridian flip, mosaic making, etc and the new setup is going to be entirely robotic. Most of this was Paul's idea. He was, pre-Covid, a regular guest here and was thinking about a remote collaboration with me. I have an unused slot in the robotic shed so we are moving a joint setup into it, initially aboard an Avalon Linear I bought from one of my other robotic clients. (Neither of my Mesus can run robotically without being converted to SiTech.) This will carry a Celestron RASA 8, due to arrive on Monday. Gorann's images with this instrument are just too good to ignore and he has been most helpful to us in our thinking. Merci monsieur! 😁 We'll be guiding with a Skywatcher mini guider and ZWO CMOS which I also bought from the same robotic client. My first CMOS camera... I'm terrified of all this IT but Paul's in charge of all that! I'll keep you posted on our progress. Olly

I don't know the modern alternatives but I just use Registar for this task. It is infallible. Olly

Big improvement. I don't know if this was spotted at the time but the first one has a misaligned ghost image in there as well. Every bright star has a tiny star just below it and slightly left. This just a misaligned duplicate image of very short duration, which is why the ghost stars appear so small. Olly

The difference is quite simple. When a daytime photographer compares F stops s/he is comparing different apertures at the same focal length with the same pixel size. His or her camera lens is shooting through an iris which opens and closes, varying the effective size of the lens. When the iris is wide open it lets in more light. When stopped down it lets in less light. Obviously, when it is wide open it lets in more light and reduces exposure time. When stopped down, it lets in less light and exposure times increase. What matters is the area of the open aperture. Each reducing F stop equates to a doubling of the open area of aperture and so a halving of exposure time. When we put a focal reducer into a telescope we are not increasing or decreasing the size of the aperture. It remains the same, so we cannot expect to find the same simple relationship between F ratio and exposure time. What we need to do is consider an assortment of telescopes of the same focal length. If we do, we can easily put them in order of 'speed,' because the one with the largest aperture will be fastest and the one with the smallest aperture will be slowest. And, guess what, this will be borne out by their F ratios, just as on a camera lens, but only because the focal length is the same in all cases. Below is a gum tree. If you compare different focal ratios at different focal lengths you will go straight up it! Only compare F ratios at the same focal length and with the same size of pixel. lly

I entirely agree. Olly

Good outer shell! If you use layers to add the Ha, why worry about the flats? You'll only be using the small central part of the Ha image and can ditch the rest. If you're not using a layers program... you should be! Olly

If the OAG is fully retracted I presume you're not using it. In that case why not remove it? It's a very likely source of unwanted reflections and shadowings. Olly

My honest opinion by way of answer; Because the ST80 is about as bad as it gets for imaging. It has a bendy focuser which introduces tilt and has terrible colour correction. A basic camera lens of far shorter focal length will, in reality, out resolve it in terms of real detail and offer a wider field of view at the same time. Olly

Round stars only tell you that the level of error is roughly equivalent in both axes. You can still be losing resolution, even a lot of resolution. That graph would be consistent with a mount with backlash falling to one side of the mesh and then being pushed to other by the guider, only to fall back again, and so on and on. However, it would be consistent with other problems as well. Have you tried the usual trick of running slightly east-heavy in order to encourage the mount to stay on the driving side of the mesh? Olly