ollypenrice

An OAG is potentially a complicated choice for guiding a small refractor. I guide a large refractor perfectly happily with a guidescope. Still, either will work. Going for OSC now makes more sense since CMOS came along. With CCD I'd still recommend mono, myself. The dual band filters bring more versatitility to CMOS CCDs. In choosing a camera your concerns should be 1) how much FOV would you like and be prepared to pay for, along with whether the corrected and fully illuminated field of the scope will cover it. The diagonal of the chip must be no greater than the diameter of the image circle. 2) Pixel scale. There's a calculator here. http://www.12dstring.me.uk/fovcalc.php With a modern CMOS camera and an 81mm scope I'd have thought almost any camera would give a decent sampling rate. The range 1.5 to 3.0 will give nice results, best towards the mid point, perhaps. At least half the imaging process is done after capture, possibly more. So you'll need a stacking/calibrating software and a post processing software. Stacking can be done in free DSS but it's very slow and with lots of short-sub/high pixel count CMOS subs it might take forever. I use AstroArt, which is excellent and also has a good gradient removal tool, something which you will need. Maybe you already have Photoshop? It's still a wonderful tool for AP. Gradient Xterminator is a good gradient plug-in if you do. AstroPixelProcessor is making friends and Pixinsight is powerful but wantonly obscure, to me at least. I do use it but find it a stressful environment. Have fun! Olly

Starnet has rather changed the game so far as star control is concerned, it must be said. I'm not a spend for spend's sake person, not at all. I'm perfectly happy with Baader LRGB, for instance. But, having used both the Baader 7 and the AD3 I con only say that the AD3 is spectacular. Olly

BIG discount for a Shelby Cobra. Free if I can borrow it for the day. If it's a genune one, not a replica, I'll pay you to come! 🤣lly

😄 Discount for rear wheel drive... 🤣lly

PS Another feature of the Astrodon data is that you can process it very aggressively, viz: This stretch raises eyebrows but both Tom O'Donoghue and I use this Curve. It will bring up the stars very strongly with 7nm data but you can get away with it in the Astrodon. A conventional log stretch will give you a softer look but a) I like the hard stretch and b) it works far better when used to enhance the red layer in an LRGB image and that's how I nearly always use it. The very high contrast is less washed out by the red channel. Olly

I'm not sure about this. I would have expected it to be the other way round, though I haven't done a comparison. What is widely agreed upon, however, is that the 3nm is significantly more moon-proof than the 7nm. I certainly find that, as do many others. A lot of that data's strong points do come from the filter. I don't have earlier Baader Rosette data stored any longer but I remember how it was. There was less contrast in the nebula and the stars were much bigger. I'm also convinced that the Astrodon is faster in reaching a good S/N level. Another comparison comes to mind. When I was working on this image https://www.astrobin.com/full/243808/0/ I was using the Tak 106/Atik 11000 for the widefield and adding 'regions of interest' at longer FL from the TEC140 and another Atik 11 meg. Normally the TEC blows the Takahashi out of the water on resolution. Finer detail, more stars, smaller stars. There is a big difference. However, 7nm Ha from the TEC really did nothing to enhance 3nm data from the Tak. The data sets looked very similar, so the 3nm was tightening up the Tak's results in a remarkable way. I was very surprised by this but so it was. However, I've also used the 5nm Astrodon and, again to my surprise, I found it closer to the Nnm Baader than to the 3nm Astrodon. The 3 is a killer filter but difficult to focus since the stars are so restrained. Olly

Just a thought from something the OP said at the beginning: If using a Newt it may be worth noting that the best orientation for your camera is as shown here on Peter Vandevelde's self-built instrument... It's the most stable position, introduces the least tilt and keeps the setup in dynamic balance as it moves around the sky. Olly

Here's a link to 24x15 minutes of Ha from a rear wheel drive Astrodon 3nm filter, Atik 11000 and Tak FSQ106N, all Mesu 200 mounted. See what you think. https://www.dropbox.com/s/3pdjgw6il2dqihm/Ha3NM 24X15.tif?dl=0 Olly

🤣 Ahem, a Mini Cooper is front wheel drive. The purpose of a proper car is to allow the enthusiastic driver to come out of corners in ego-boosting, power-on opposite lock slides. Front wheel drive cars are for going to Sainsbury's and for letting schoolboys perform what they call 'lift-off oversteer.' AKA oversteer for nancies. 👹😄 Olly I am, of course, joking. Sort of...

What interests me above all, here, is the performance of the new narrower bandpass Baader narrowbands. I have the 7nm Ha and the whatever-it-is-eightish nm OIII. The Ha is OK, quite good, but the ridiculously expensive 3nm Astrodon is simply way better. While holding down the stars it pulls out far more contrasts, in less time, than the Baader 7. However, you can work with the Baader 7 and get good results. How would I quantify the difference? If you want to make a good NB-enhanced broadband photo I'd say the Baader 7 would give 80% of the Astrodon 3. If you want an excellent all NB photo then the Baader drops to 50% of the Astrodon. And the harder you want to push the contrasts from the Baader the more extra exposure time you'll need. This seems to be a minority opinion on this thread but I can't help that and I have hundreds of hours of using both. So now for the Baader basic 8 (point whatever) OIII. It's junk. I have two of the wretched things and they are halo maniacs. I also have a replacement Astronomik for an original which was junk and the replacement is also junk. More halos. I tried to order a newer, tighter bandpass Baader OIII but just kept getting emails saying it was still not available in the format I need for my FW. I lost the will to live. I can only live with my present OIII filters because 1) I'm a shameless post-processor and can bodge most things (not a virtue) and 2) because I don't do pure NB imaging, I only add NB to LRGB. This makes it easier to bodge the pestilent OIII halos I have, but I would like to offer better raw data to my guests. So, for those who've tried them, what are the new, tighter, Baaders like? The million dollar question. Olly

Monochromatic means 'one colour.' A luminance filter is only monochromatic in the sense that it can only deliver an image in one colour. By default that would be greyscale but you could colour it red or blue or whatever you like. But you have no way of separating the colours in a luminance image. However, a luminance filter is not a monochromatic filter because it passes all colours, so it is, in fact, a polychromatic filter. Therefore it needs a fully colour corrected lens. A narrowband filter is nearly monochromatic in that it passes a very narrow selection of colours (Ha passes a narrow range of deep reds, OIII passes a narrow range of colours on the blue-green border, etc.) A badly corrected lens will have blue bloat in luminance and blue. It will not have the same bloat in red or green so the bloat will appear blue in LRGB. It will be worse in blue than L because all the light in blue will be bloated whereas in L the green and red will not bloat. But the L will show bloat for sure. Olly

I used the native FS60 to get huge blue bloated stars. Reducers, no I think that's a good solution provided they work. Generic ones cannot be relied on to work in all scopes, though, even ones within the specified range. I would want to see evidence that a particular combination would work before buying. Also it is important to be realistic about super-fast effective F ratios. I'd be wary of anything below F4. Fluorite is fine, too. I have an old fluorite FSQ106 in which the F stands for fluorite, not flatfield, but the best imaging refractor I've ever used is an ED triplet, the Tec 140. It is significantly better than the FSQ106 though it's a slower F ratio, to be fair. Olly

The scope! The actual real world scope, not its specification on paper. Sorry I wasn't clear. Olly

tHE THING

I don't know the latest scopes but that's a very short FL for a telescope. My point was a general one. If we start by thinking of a 300-320mm FL then we have to factor in a realistic F ratio for a budget design. F6 is potentially possible but that would mean a 50mm aperture. If you go to 60mm you'll need F5. Can anyone make well corrected F5 optics in a scope of adequate quality at a budget price? I would be surprised, I'm afraid, but I would be glad to be proven wrong. I'm wondering about prime camera lenses, possibly older, non-stabilized designs. If you make a simple front aperture mask you can stop them down without introducing multiple spikes from the diaphragm. By the way, the Tak FS60, unless it has been greatly improved since the ones I tried about ten years ago, could not blow anything away. They were awful deep sky imaging scopes with dreadful blue bloat on hot stars. Olly

Some of those images would have masses more to give with better processing. Why not post a Dropbox link to that first Double Cluster as an unprocessed stack and see what help folks can give? You mention a line on your chip which you are cutting out by black clipping, if I have this right? There are better ways, for sure, to make lines disappear! I won't comment on how to spend 300 quid but I'd be happy to help with processing and that would cost nothing. Olly

I think it's important to know that the mechanical quality is very important in imaging scopes. There are plenty of examples of focusers which slip or sag, introducing the problem of tilt. There also good and bad lens cells which can pinch the optics or be impossible to collimate. And refractors must be collimated to work well. (Takahashi have been guilty of supplying an alarming number of miscollimated FSQs in the last few years.) In the real world, when you are on a budget, a simple optical design is likely to beat a complex one because it is more likely to be supplied in good working order. One of our regular guests has a TEC140, which is obviously a brilliant scope, but he also swears by his TeleVue 85 doublet. On paper this is an old design but he takes great pictures with it. My general point is that you are far more likely to be limited in your success by mechanical problems, or collimation, than you are by what numbers define the glass type or by how many elements you have in the tube. We don't take pictures with the spec sheet, we take them with the thing on the mount! As Valiv says, look at the forums to see which scopes are consistently delivering good pictures. Olly

Strictly speaking, it's incorrect to regard the fan as being there to cool the scope. Its purpose is to help all the components reach ambient temperature, so if you took the scope out of the freezer to use it the fan's job would be to warm it up! What I'd do would be run the fan during the setting up period then switch it off while imaging. Olly

Doesn't look like guiding for the reason Dave identifies. Is the scope well collimated? This is normally very easy since the primary mirror is spherical. For future reference, when tracing guiding issues it's best to begin by identifying the orientation of the camera relative to RA and Dec. When possible it's a good idea to have the camera aligned orthogonally either in Landscape (long side along RA) or portrait (long side along Dec). That way you know at a glance which axis is misbehaving and you'll also be able to repeat the framing easily in the future to add another panel or just add more data. A sort slow slew while exposing will produce a star trail showing the present orientation. Olly

Excellent! Personally I'd have the original focuser over the Moonlite but I'm notoriously allergic to Crayfords. 🤣 It might actually be better for doubles, I'll admit. A good 4 inch refractor has so much going for it and here you have one of the best ever. A bit of the famous 'hospital green' does gladden the heart. Olly

GoTo and autoguidng are two entirely unconnected things so you can autoguide a non GoTo mount, certainly. GoTo does make imaging much easier but it isn't compulsory. There are two main ways to autoguide, both using the free PHD 2 software. The original way, which I use, involves plugging in a USB connection between guide camera and PHD on the PC and also connecting the camera to the mount using an ST4 cable. (The term ST4 cable is not strictly correct but the term is universally used and understood. It looks like a phone cable but beware, it's not wired in the same order. Buy it from an astronomy supplier.) I don't know if your camera is known by default to PHD2 but, if it is, you choose that model and select 'On Camera' in PHD. You'll find plenty of How To videos via Google. The other method involves using pulse guiding in EQ Mod. I don't use that method so will let others explain it. Have fun, Olly

I would certainly lose the flattener because there is no need for it whatever with an APSc chip. You're needlessly introducing more glass and more possibility for tilt. (My Tak 85 focal reducer introduced some tilt till I loosened the three radial screws, pressed the whole assembly down on a table and re-tightened them. Then it was fine. I'm not really sure what is meant by 'butterfly stars.' I can see the familiar Tak 'inverse lighthouse beams' like this: My FSQ85 did this and my 106 also does it. It never bothered me much. Greg Parker thought it was pinching of the optics but I don't know. Could you post a close up of this 'butterfly' effect? Vignetting: rather than guess at its extent it is easy to measure. Take a linear flat, or linear master flat, and read off the ADU in the corners, then in the middle. The light fall-off on my old fluorite FSQ106 is enormous, about 23%, which is made slightly worse by my using 2 inch mounted filters. A friend's similar scope with 2 inch unmounted filters is a few percent less vignetted but, after application of flats, this matters not at all. Above all I'd like to know what you feel is wrong with the stars if it isn't the 'beam' effect. Olly

Most kind, Dave. The real credit for the project must go to Yves whose data were at the heart of it. I dare say my copy will make it through Kent in a year or two! lly

Monique always says, 'It looks very red.' My excuse is that hydrogen's the most abundant element in the Universe but she's never conviced... Olly

It's at the stacking-calibrating stage that you'll need computing power. The software you choose for this task will be more or less demanding. For a very fast, efficient choice you could do worse than AstroArt, which has some other useful tools, notably a decent gradient remover. The HEQ5 is a good choice and really isn't expensive when you reflect on what you're asking it to do, which is allow you to image with a tracking precision of significantly less than one pixel or about half an arcsecond. (That's under guiding. The native, unguided error will probably be forty times that.) Starting with your lenses is a good idea but there is a lot of glass in zooms and stars are murderously exacting targets. Primes are preferred for AP. There's so much to learn that you'll need some imaging time in which you're looking to make the system work rather than take perfect pictures so starting with the lenses would be fine. Olly