ollypenrice

Aperture does two things. For a given optical quality it increases optical resolution and it collects more light. Only the first of these advantages is negated by bad seeing. The increase in light grasp is unaffected. Olly

A successful experiment. I'll admit to being pleasantly surprised by how well you've done here. Olly

This thread has sent me back to my TEC140 data on M51. My offically 'best' M51 combines this 12 hour run from the TEC 140 with a longer run using Yves Van den Broek's 14 inch ODK. So with a bit of tweaking, shoving and thuggery, what can I squeeze out of the TEC140 data? This is, remember, only 12 hours in HaLRGB. I'm chucking it in here at full size and cropped despite the fact that this will throw up JPEG losses for all to see. I don't claim a big reflector can't beat it. I just wonder by how much and with what degree of hassle? Olly

You'll get answers from theory but what you need is answers with the subs... Olly

A friend down the road has a 175 Starfire. Thank God he isn't selling it! Olly

These are cogent arguments but are predictated upon using CCD technology. For better or worse CCD chips will probably go out of production to be replaced by CMOS. What are the binning advantages of CMOS compared with CCD? Olly

Whoa, the big question is, What will your seeing support? If your Mesu is anything like the two that I use it will run an RMS under guiding of about O.3-O.4 arcsecs, which will support, at worst, about 0.8 arcsecs per pixel. But what will your seeing support? You'll need a darned stable night to let you work at 0.8"PP. I'm not saying it won't happen but how often will it happen? Personally I've given up on big reflectors and opted for a focal length of a metre and the simplicity and reliability of refractor optics and a camera with suitably matched pixels to give me a pixel scale of 0.9"PP. Payload is absolutely not the problem. Seeing is the problem. Olly Edit. One more consideration. Pixels are getting smaller. Do you want to end up with a focal length entirely inappropriate to these cameras? I can't read the future but my impression is that it is not going the way of the big amateur reflector.

John's right. Olly

That's good. The red fringe is showing around the Owl and the galaxy is looking convincing in this one. Olly

They do pop up. There are two of them working at my place at the moment, one of them mine and both bought on the used market. Given my worldview I'm a little alarmed to be described as having delivered sermons! Please just look at the pictures, for which I have to thank TEC, Atik, Lucas Mesu and the software engineers on whom, like most of us, I depend. Olly

Unusual target nicely done.

Pretty good core detail. There is more in the outlying disk which would be better if you rotated 90 degrees. Ha is exciting in this object but I don't know how well that would work with one shot colour. Probably quite well. Olly

F4 is fast and best used with expensive, well-made mechanical parts. It will need good collimation and careful coma correction. Some succeed, some don't. Once I've said that I'm no longer in the realm of hard facts and so I'll stop there. Give it your best go. You may be delighted. Olly

One thing's for sure, the darned thing has irritable vowel syndrome. Olly

In order to get an accurate and meaningful view of the histogram in Levels you need to edge crop the image. If this change in size is going to cause you problems when you want to combine another layer using the same or matching data then, rather than edge crop it, you can exclude the edges by creating a large marquee selection and looking at the histo within it. Continue to process within that selection. If you still have a gap on the left before the start of the data line just move the black point in to meet it. This will give you the full brightness range for continuing. You don't want any edge artifacts appearing in the histo. Some CMOS cameras have a reputation for amp glow on the right hand side of the chip if I'm not mistaken. I haven't used a CMOS but a bit of internetting on that term might give you some answers. Why don't flats correct it? I'd guess that their short exposures don't produce as much glow but that's a guess. With CCD you can use bias (offset) as a universal 'dark for flats' but with CMOS you cannot. You should take darks for your flats (AKA flat darks) on the same settings as your flats. It's just possible that doing so might solve your problem. I'm not sure what purpose your bias frames are serving at the moment. You might be better off without them. Olly

Just be aware that LRGB with a mono camera is faster than OSC. The LRGB system was invented to save time. (A colour filter over each pixel means that the two other colours are blocked so the total light per pixel is reduced. During the luminance phase of the capture all the colours are reaching the mono camera's chip, so saving time.) Shooting through 4 filters is not 4x slower than shooting through the three fixed filters of an OSC. It's generally considered to be about 20% faster. Olly

Nice. Way better with the colours balanced. Olly

The Rolls Royce of tools is Pixinsight's Dynamic Background Extraction. Russ Croman's Ps Plug in Gradient Xterminator is also good and AstroArt, which is a great stacking and calibrating routine, has a decent gradient tool as well. You can do quite a lot manually in any graphics program offering layers ad curves, too. Olly

That's a great offer. Olly

The moon really is bad news on broadband imaging targets but the galaxies look very promising. The stars are a little strange, though focus looks OK. They are very blue-dominated which suggests you may have to work on balancing the colours. Olly

Gosh, I hadn't seen Pete's images on Astrobin but they are quite superb with the TS instrument. Olly

I've used these people in France: https://www.monoeuvre.fr/decoration-murale/photo-sur-acrylique.jsf They do astrophotos pretty well and don't do any reprocessing. I'd offer two pieces of advice when processing for printers. 1) Make sure your background sky is a little lighter than you've set it in your screen version because print will pull it down again. 2) Be sure not to have your brightest details too close to the saturation point. Print seems to white clip to some extent. Olly

The sampling rate, as you're already suspecting in your post, needs to be considered in terms of what kind of target you're imaging and how you want to look at the picture when it's finished. Most galaxy images projected onto chips by amateur focal length telescopes are small. For the final image to give a decent screen size and contain pleasing details the pixels of the chip must, therefore, also be small. A sampling rate of about 1"PP will offer this. Much below that and you'll be very lucky not to see the theoretical level of detail blurred out by seeing and guiding effects. Once you have this image you'll want to show it at 100% (AKA full size), meaning 1 camera pixel is awarded 1 screen pixel. To dispense with the need for your viewers to zoom in to this scale you'll probably want to crop out some of the surrounding background sky. This is an example of a small, delicate target to be shown at full size. About 1"PP is necessary. (This will also require you to shoot a lot of data because full size presentation is very, very intolerant of noise.) Most of the larger nebulae are quite diffuse and contain few tiny details, certainly fewer than galaxies. Their projected image covers most of the chip and many may need a mosaic. The idea is to present the entire nebula, which means you won't want to crop the image. It might be nice to present it full size so that viewers can zoom in and see the smaller details but that is a luxury, not a necessity. Although the tiniest details, where there are any, will not be resolved at coarser pixel scales an image shot at up to 3.5"PP will still look smooth, un-pixelated and and have round, rather than 'blocky' stars. For presentation at full size I would not, personally, go above 3.5"PP. Widefield images are not generally intended to be zoomed in on unless they are made at high-ish resolution and constructed as mosaics. If not zoomed in on they will look fine, as you point out, at far coarser pixel scales. Finally, if there are images you like taken with Equipment X then Equipment X will work for you once you've mastered it. Olly

Probably better to be slightly undersampled than over. (Mainly because it's faster.) An EQ6 working well under guiding can deliver an RMS of about half an arcsecond. The generally accepted rule of thumb is that this will support imaging at about twice that, so an arcsecond per pixel. Note that it is very common for the seeing not to allow this, unfortunately. I'm not up to date with all the possible cameras and haven't used a CMOS, so others will need to advise on that. It's certainly true that the arrival of small pixel cameras has opened up the galaxies to refractors. (I did an article on this for Astronomy Now a while back.) BTW I think there's a calculator for pixel scale on FLO's website. Olly

Careful, the sensor size has precisely no effect whatever on on what you're calling your 'reach.' Some of this confusion comes from the horrible term 'crop factor' used in daytime photography. This term encourages the mistaken belief that there is some equivalence between focal length and chip size. In astrophotography no such equivalence exists. The proper term for 'reach' is image scale or pixel scale, measure in arcseconds per pixel. It is controlled by just two variables, pixel size and focal length. Not chip size. More care needed. In daytime photography a lower F stop is faster because it has more aperture. A 120 has more aperture than a 100... This topic is contentious and has been done to death on here (partly my fault!!! 🤣) but a quick search on the fatal term 'F ratio myth' will reveal all, even though it may leave you none the wiser. Unfortunately this is rather like saying, I want to buy a sauce mix which works for fish and cakes. Nebulae and galaxies are very different. Galaxies, apart from M101, M33 and M31, are small (and packed with tiny details requiring high resolution.) Nebulae tend to be large, diffuse and lacking in fine detail. Finding a scope-camera that will do both is not easy. The nearest you can get is to use a moderate focal length (approaching a metre) and a camera which has both small pixels and a large chip. This is always going to be expensive. Old Eyes, above, mentioned our TEC140. This can do a good job of nebulae and galaxies if we vary the camera. Here are two examples, the first with a large format, low res, large pixel Atik 11000 and the second with a small format, small pixel Atik 460. There are now cameras with both large format and small pixels using CMOS technology, however. Olly