ollypenrice

...and they mire themselves in that nightmare term, 'crop factor' in which chip size risks becoming an equivalent of focal length. (They also mire themselves in the notion that full frame cameras have a greater depth of field but this is only because, at present, full frame cameras tend to have larger pixels.) It is the astrophotographers who have the proper understanding of focal length, field of view and resolution. (Says an astrophotographer! ) Focal length is written on the lens. Chip size determines field of view. The ratio of focal length and pixel size determines resolution measured in arcseconds per pixel. Deviate from these simple facts and you plunge into the mire! Daytime photographers do have an interest in perspective, however, since the naked eye creates a relationship in size between foreground and background objects which they may wish to preserve or to over-rule and here the vile term 'crop factor' might be spared from summary execution! Astrophotographers always work at infinity. (Infinitely difficult, infinitely expensive, infinitely exasperating...) Olly

No, it could be worse than that. OK, I'm out! lly

I spent about 2 hours setting up, and trying to get the guiding tuned, and mostly I was getting RMS error of less that 2 degrees, with most of that being DEC (I assume my PA wasn't as good as I thought). I shot 60 lights at 180 seconds iso1600. I shot darks, flats and bias. I think this must be a mistake. A 2 degree guide error would be nearly eleven times greater than the apparent size of target itself, which is about 11 arcminutes across! A well tuned EQ6, properly autoguided, should be able to achieve an RMS of about 0.5 arcseconds. That will support an image scale of twice that, so an arcsecond per pixel. You might get this straight out of the box on night one, but don't bank on it. This means that there is little point in building up a system which tries to resolve at less than 1"PP. Even that might be pushing it if your seeing is not excellent. (Note, seeing, not transparency.) So, for galaxies other than M31, M33 and M101, aim for something like an arcsecond per pixel and you are likely to be aiming for the possible. This game is hard enough without aiming for the impossible. This is a useful calculator: https://www.12dstring.me.uk/fovcalc.php Olly

I can think of many reasons for not making toilet tents with sewn-in groundsheets, none of them likely to go down well with the moderators! 🤣 Olly

The experts in solar system imaging use video footage from which they extract and stack the best frames from the shoot. This gives a far better result than a single exposure. Your camera will shoot video so that might be worth a try. You'll need appropriate software like Registax or Autostakkert for the processing. When shooting stills at prime focus (the telescope becoming the lens) you only have two variables, ISO and exposure time, so it's easy to experiment and find what's best. Olly

That's about it but the terms are very vague. In imaging the situation has been somewhat altered in recent years by the arrival of cameras with tiny pixels. When pixels were typically 7 to 10 microns or so, an imager would have wanted well over a metre of focal length for the smallest targets but this is no longer strictly necessary, so a metre has gone from medium to quite long in deep sky imaging terms. Olly

It depends on what you want to do with the instrument. If you want to do deep sky imaging at a short focal length (350-500mm or so) with a 35mm sensor you really don't have much choice and a Tak FSQ106 with reducer (or even without) is almost certainly going to be on your shortlist. There was a very fast 4 inch Pentax (which made a come-back under another name IIRC) but that was simply not as good either in flatness of field or star control. If you are not going to use such a large sensor then the FSQ suddenly runs into stiff competition, especially if you don't mind a slightly slower F ratio. It would be nice to think that Tak prices meant top quality control but there have been plenty of cases on here and elsewhere of mis-collimated FSQs straight from the dealer. This really is not good. Nor is it good that some people feel the need to fit Feathertouch focusers to their Tak FSQs because the Tak focusers are problematic. (I've just been fiddling with one belonging to a client in our robotic shed.) A fully sorted FSQ106 is a remarkable refractor and will give you better results on a full frame chip than anything else I know of at around 500mm. (But I don't know all the alternatives.) I think what Tak do really well is make great doublet/triplet scopes for visual observing and they seem to be on top of QC in this part of their range. But should we worship brands? I don't think so and, if I were to worship a brand I use, it would be TEC, not Takahashi. Olly

I don't think the usual 'rules' from regular photography get us very far in these conversations. What we are interested in is how much light arrives on each pixel. This depends on the ratio between the pixel size (its area) and the area of the aperture. F ratio does not define this ratio, nor does focal length. Now, each pixel receives light which includes both light from the object and light from polluting sources. On very very widefield images the LP will be worse in one part of the image than another. (It will always be worse near the horizon and may be worse in the direction of a city, etc.) But, other than that, a lens with a wide field of view is no more or less susceptible to light pollution than one with a narrow field of view. If you want a rule of thumb from readily available information, forget F ratio and forget focal length. Both are likely to lead you up a gum tree. Just look at arcseconds per pixel. This tells you how much sky illuminates each pixel. Obviously, the more sky illuminating each pixel, the more light each pixel gets - and that will define your exposure time. Olly

Absolutely, yes, but I speak personally. I use it all the time, on all projects, but sometimes its role is fairly minor. Sometimes it's critical. What do I do with it? - align colour channels when, exceptionally, my regular software (AstroArt) fails to get it perfect. - align L to RGB. All sorts of software will do this but I process RGB first, look at the data and edge crop as necessary in search of a perfect crop to take into DBE. The first thing I then do with my L layer is align and crop it to fit the RGB in Registar, after which I know it will be a perfect fit over the processed RGB. - align, resize and crop/pad existing data to fit new data on a target. Many of my best images are composites of data taken years apart with different setups. Registar deals with this in a couple of clicks. - align, crop and pad data from our dual rig so that these data act as though they had come from the same instrument. - construct mosaics, including mega-mosaics like my collaborations with Tom O'Donoghue on Orion and Yves Van den Broek on Cygnus-Cepheus. - make small crops during a processing job knowing that I can go back to earlier data and use Registar to make it fit the later crop in five seconds. Very relaxing. - combine data an wildly different resolutions (camera lens with 2.5 metre focal length) to consider new projects. And more but my wife is calling me! Olly

Since objects rise in the east and set in the west you are going to have rising objects, circumpolar objects and setting objects, so only the circumpolar ones will have visibility at their highest elevations. You won't see the easterly and westerly objects at their best. You will have less variety during the year, as well. Olly

You're a very experienced observer, though. It's much harder for beginners to aim a scope, I think. Olly

I wouldn't suggest a Telrad for binos, only for a widefield scope. Olly

Preprocessing, page three. I think it's called 'extras.' It's full of great features. As well as hot pixel removal you have column repair. Since dead columns are just a fact of life in CCD imaging you select Column Repair and type in the number of the dead column on your chip. It will be repaired by giving each pixel in that column the average value of the pixels to its right and left. The dead column then simply disappears. (To find which column it is just open a sub on which the column shows and mouse over it. Put the cursor on the column and look for the x value at the bottom of the screen. If x = 2234 then 2234 is your dead column.) I write it down on a bit of paper and stick it next to my screen. You know what I'm like!! 🤣 I have lots of bits of paper because I use lots of cameras...😜 Olly

Did you try the hot pixel filtration in AA, Carole. It is adjustable in intensity and gets nearly all of them for me. There should never be any need to clone them individually. I've lent the camera to Tom for a while for his robotic rig so don't have a dark in stock but snowstorm is the word. Who cares? It's the picture that matters: https://www.astrobin.com/383965/?nc=user https://www.astrobin.com/321869/?nc=user I do hardly any small scale cosmetic cleaning after stacking. Quite often I do literally none at all. Olly

We all use some kind of finderscope on our main one. A widefield instrument like a refractor is best served by a reflex sight such as a Telrad or a 'red dot finder.' https://www.firstlightoptics.com/finders/telrad-finder-astronomy.html This device creates three red rings like a target seen on the sky and has virtually no parallax so it shows just where you are pointing. It does not magnify and has no tube so you can have both eyes open. It does not restrict your view. A scope on an alt-az mount will stay still while you estimate the position of the Telrad on the sky and plan your next hop. Both paper and computer star charts can have Telrad circle overlays placed over them. This makes life very easy. Your 32mm Canons do rather lack light grasp fr astronomy so 70mm would be a considerable change for you. (I forgot to check in your signature, sorry!) Olly

It is good practice to have bolts protruding down from the front and back of the dovetail bar when you get your mount. They will stop the dovetail slipping down through the clamp on the mount (known as the saddle plate). This is a well proven accident!!! Olly

Your image stabilized binoculars will probably have quite a high magnification. Which ones do you have? And being Canon they will give a very good image quality. You risk being very disappointed by any improvement or great change from budget 15x70s. I use high quality 8x42 binoculars and budget 15x70. To be honest I rarely use the 15x70 any more because they do not make for a fundamentally different observing other than by requiring a tripod. That's a lot of palaver for a not-very-different experience, the light grasp and magnification of the big ones being offset by the inferior image quality. Pointing them is also harder than pointing a small telescope on an alt-az mount. (I use a medium photo tripod for the 15x70.) The advantages of a 70-80mm telescope over 15x70 binoculars are, in my view, - The option of high or low power for galaxies, planets, nebulae and the moon as well as the possibility of ultra widefield viewing with a long FL eyepiece. - Easier pointing from using a dedicated alt-az mount. - More comfortable viewing by using a 90 degree star diagonal. - Better optics from eliminating the erecting prism. Nutshell: I would rather observe at 15x in a small telescope than in binoculars unless I had a parallelogram mount and even then it would be marginal. Olly

OK, I'll say it. I prefer my Kodak chips to my Sony. If I wanted to take and publish dark frames then I would go for Sony every time. The dark frames are great. But I actually want to take and publish astrophotos. The real business begins when you start to post-process a calibrated stack. It is at this point - and only at this point - that you begin to appreciate the Kodak data. I find that it behaves itself. I don't have to fight it. In particular the background sky and the bright stars just sort themselves out. The Sony chip's background sky will not come up to a natural brightness 'naturally.' We think of noise as being unwanted extra signal. That's not my problem. I have a problem with overly dark pixels in a stretched background sky and a background sky which remains too dark for comfort. (I have tried all the calibration options like darks, no darks, bias-as dark, etc etc. Nothing much changes). Then the stars just aren't what I want. When I added a Sony chip to my line-up, sharp observers like Sara Wager said my stars were not what they used to be. Quite right. What was the 'secret' of my previous stars? An Atik 11000. That's about it. In post-processing I have to fight my Sony data all the way. It may be lack of well depth but I'll leave that for the theorists. Call this a minority report! Olly

Hi Peter, If you have a high resolution rig which works... my advice would be, don't fix it! I'm not dismissive of statistics in imaging but I'm wary of them. They are often over-ridden by realities which don't appear in all of the numbers. One mystery concerns SCT star sizes, which tend to be rather large. Why this should be, when they are so good on the planets, I have no idea. Perhaps the latest processing techniques using Starnet to de-star an image, before a careful re-starring operation, might eliminate this issue, I don't know. While the corrector plate keeps everything clean, as you say, it is also a big piece of glass bringing issues like dew and scatter into play. Then there's cool-down... Can you really beat an arcsecond per pixel with the seeing you have? With the QSI you only need just over a meter FL to get to that. I found that there was precious little advantage to be had from a 2.4 metre FL instrument at 0.6"PP over a 1 metre FL instrument at 0.9"PP. Being a 140mm refractor the latter instrument was easier in all practical respects, though it wasn't any cheaper. I strongly suspect that, after a little over a metre, your FL won't be adding any value. Nor do I think focal ratio, in itself, matters. What matters is the ratio, area of aperture to area of pixel. As CMOS cameras with increasingly tiny pixels get better and better it remains to be seen whether amateurs will continue to use long FL scopes. Professionals will still want big scopes but they have access to big pixels. Olly

This is an optical viewfinder? When you look through the viewfinder the eye is responding almost instantaneously to the incoming light. The atmospherically induced turbulence (the seeing) is causing the image to move around slightly but the eye sees it at any one instant in that movement, so it appears sharp. When you take an exposure of a fraction of a second, any movement during that time is recorded and appears as blur. I think it is inevitable that the eye view will be sharper than a single exposure. The ultra-sharp lunar images you are used to seeing on forums are made by taking video footage during which there will be a decent number of lucky moments in which the seeing was good enough to allow for a particularly sharp capture. These lucky moments are then selected and combined. A digital photo is a set of measurements, one per pixel. It is always the case that the most accurate way to measure something is to make many measurements and take an average. So it is with stacking multiple sub exposures. Do you not have a video mode? If not, even a basic, inexpensive fast frame camera will beat a stills-only camera for lunar imaging. Olly

The mono learning curve should be a half inch curb, not a cliff! I do all my stacking and calibrating in AstroArt which also has an image alignment tool. I'm sure any astro-specific stacking/calibrating software will have the same facility. I don't know Siril but I think it must have it. Maybe try a question mentioning it specifically? Olly

Same for me. I'm fine with binoculars but prefer monocular observing with a telescope. I find binoviewers add complexity in terms of getting everything just right in terms of position, diopter, etc and then don't add anything when that's done. The OP might simply find that a monocular rather than binoculars worked better for him? Olly

Probably a filterwheel in there as well? They usually add about 19mm. Olly

Artemis is absolutely brilliant, as is the camera. Hang on in there. As Tomato says, it is virtually live view if you use short subs and bin 2x2. What do you see on the capture screen in Artemis? If it is jet black when you take a short sub the camera is saturating or has another connection issue. Are you dead sure your finder is well aligned? You might be missing the star in the main scope at long FL and with small chip. If unsure, try pointing at a tight open cluster instead of a single star. It is a small chip so an out of focus star will easily exceed its edges giving a fairly even light glow. Be sure that you are letting each sub download before you make another movement to the focuser. The expoure coundown shows in the lower right of the screen. This may not work with CCD. An excess of light will just saturate the chip and cause it to show jet black. Olly

Having just received a generous £50 voucher as runner up in the last IKI observatory processing challenge, I opted to put it towards a new spotter. My elderly Nikon fieldscope never made it from the UK when I moved to France 18 years ago so I've been using a TeleVue Pronto for wildlife. (We have a good selection from the front door here.) With fixed FL EPs and considerable bulk this is a cumbersome solution for a quick grab-and-look and the view, I suspect, is compromised by a rather basic erecting prism I use. Wanting something I wouldn't be frightened to leave in the car, I went for this very budget instrument. https://www.firstlightoptics.com/hawke-spotting-scopes/hawke-vantage-20-60x60-spotting-scope.html FLO's website worked sweetly, the few days' quoted delay was just that, the website found my voucher automatically and Steve patiently answered my silly question about how the post-Brexit pricing arrangements worked. And, hey presto, it arrived this morning. Packaging was as good or better than anything I can remember and knocks Amazon into a cocked hat. So a big thanks to FLO for the prize and the excellent service. In time-honoured manner we had another arrival just before the 'scope... Here's the instrument. The slightly springy tripod is included, as is a tough bag and a Pelicase-like box of excellent quality. The tripod will be fine for leaving in the car and using if I forget my ballhead photo tripod. But what about the 'scope? How good can it be for the price? My regular test is a mobile phone mast about 150 metres away, on which assorted plaques have text of different sizes. Hawke versus TeleVue (with indifferent prism) : despite looking through a veil of snowflakes the Hawke won. Seriously. The smallest text was clearer than I've ever seen it in the Pronto without snow. The Hawke's zoom EP gives a smaller FOV than the TV's Radian, naturally, but the Hawke's is a zoom, which is a huge benefit in a fieldscope. And it's so light and handy that it will, I'm sure, get lots of use. In a nutshell, outstandingly good value. Olly