ollypenrice

Agreed. With decent filters the non-parfocality comes from the optics. Olly

Simply inserting a length of square section metal tube between the dovetail plate and the tube rings will probably give you the extra clearance you need. One of my robotic clients uses this system on his rig. Olly

There's nothing much to it. This calculator will tell you the resolution in arcsecs per pixel. http://www.12dstring.me.uk/fovcalc.php To get a reasonable image scale you'll need about a metre of FL with the 460. Longer will certainly over-sample but you can bring it down by binning. (My galaxy imaging is done at 1 metre focal length with the same Atik 460 as yours, giving about 0.9 arcsecs per pixel. That gives a satisfying image scale and is usually achievable in the real world.) You need to give PHD your guidescope FL and pixel size then it will give you the guide RMS (in effect the error) in arcseconds. The RMS needs to be no more than half your image scale if you are going to lose no detail to guiding error. I could bin colour (making 1.8"PP) but don't. I just don't like it and I often want to make my stars out of RGB only, so I want them small and tight. However, I'm not usually fighting endless cloud (right now being an exception!!!) so I'm not under pressure to bin. The 6 inch RC looks promising but don't expect it to be easy to collimate. Olly

I wouldn't touch a fancy flats-capturing software option with a ten foot pole because I always want to know what's going on. I always make master flats exactly as if they were lights except that I combine them using a simple average rather than a sigma routine. And I do this before applying the master flat to the stack of lights. You'll need a master 'dark for flats' as well, so first you need to find your flats exposure time and gain and then use them again to make darks for flats. I would be absolutely paranoid about light leakage as well. Light has an uncanny ability to get past things intended to keep it out. Olly

Yes, just a dust bunny I think. They are only rarely caused by dust on the filters. The chip window is a batter bet. I agree with jimjam, above, that collimation my be out. Star shapes don't look perfect and in some cases the top edge of the star looks a tad sharper than the bottom to my eye. Olly

I don't believe small adjustments in focus will require changes in flats. I certainly never do flats 'per focus position' and most of the time I only use lum flats. Sometimes they last for months, sometimes a dust mote will move. Pot luck. A couple of people mentioned doing darks 'per filter.' This is meaningless because darks must be done with no light entering the camera, in which case it matters not a jot which filter is in position. Olly

I just finished the book this morning and am more glad than ever that I read it. While the chronology is sometimes a little disjointed, leading to moments of repetition, and while I was never entirely convinced that the author had really found Fritz Zwicky, this man had such a huge personality that an imperfect portrait can still be resoundlingly worth studying. About the only Bill Bryson book I haven't read is his Short History of Nearly Everything. According to Zwicky's biographer, Bryson rather plays Zwicky for laughs and quotes his scientific detractors. If so, this won't do at all because Zwicky, at his best, was one of the most penetrating astronomers in the history of science. His prediction of the neutron star some 35 years ahead of the Crab Pulsar discovery and his discovery of the missing mass/dark matter problem speak for themselves. Let's hear it for Fritz Zwicky! Olly

Round stars: what do you think round stars are telling you about your captured resolution? They might be telling you that you have perfect tracking or, at least, tracking so good as not to impact on the final resolution. But they might just as easily be telling you that your tracking errors are about the same in both RA and Dec. Our first Mesu gave round stars from the outset once we fired up PHD. However, they were large round stars and only when we had found the right guiding parameters, giving an RMS of about a third of an arcsecond, did they become small round stars, meaning that the mount was guiding well enough for the image scale we were using. (0.62"PP.) Have you measured the PE of your mount? It needs to be less than about half the image scale at which you are working. Given that a standard HEQ5 might be expected to have a PE of about 20 arcseconds your belt mod is going to have to have had an almost supernatural effect for it to bring the mount anywhere near the accuracy you need. Thinking very roughly and making the crudest assumptions, 3 minutes is about a third of a turn of the wheel which might equate to a third of the total PE, so about 6 seconds of arc. This would support a finest image scale of about 12 arcseconds per pixel. With the ZWO 1600 you're at about 1.6"PP so you actually need an RMS of about 0.8 arcseconds. If the quick calculation above is anywhere near correct (my calculations never come with a guarantee!) you certainly need to guide. Olly

But of course it is! It even merits a black and white picture taken on hypered 2145. Apparently it can be seen in direct vision in scopes of 12 to 14 inches so we can take a look at it while we're imaging... Olly

Or Photoshop, but you really need both! 👹 lly

Ooh yes, nice! These are new to me. Super processing. Olly

No brainer. Go for a mono camera and narrowband imaging. Either buy second hand or wait till the CMOS camera does fall within budget. Olly

I've never got a grain of sense out of Straton but that doesn't mean you won't! ly

What I find is that my 460 camera produces a noisy background sky without calibration. The noise takes the form of a lot of overly dark pixels so, after stretching, some background pixels will be at 23 but others will be far below that. Olly

Fabulous. Controlling the stars really is the challenge with the widefield Veil. I must have a go with Starnet. Olly

Well done! This is clearly a challenge but the image goes deep enough to make the target well worth while. Excellent. Olly

Nice gentle processing. Lovely. Olly

That's perfect. Well it just is! Olly

One discovery I made is that using a master bias as a dark works fine at -20C but does not work fine at the -8C which is all I could manage on our warm summer nights. At -8C I got visibly cleaner stacks using proper darks. So the temperature does matter, even with the Sony chip. I think -10 should be OK but I would use darks with it. Olly

I use CCD cameras. The situation is not the same for CMOS chips. I find with one of my cameras that it continues to go deeper up to about 30 minutes so, if I'm chasing faint signal, that's what I use. The other camera seems to stop gaining after about 15 minutes so, again, that's what I use. You actually have considerable flexibility in exposure times doing AP. It is not comparable with daytime photography in this respect. There is an elegant way of combining short subs with long in Photoshop. http://www.astropix.com/html/j_digit/laymask.html Surprisingly, perhaps, there is hardly ever a need to do so but the famous target for which it is essential is M42. This had 11 seconds, 50 seconds and 15 minutes: https://www.astrobin.com/380941/?nc=user Regarding the numbers I quoted over guiding, it's very simple. A basic, decent mount like an NEQ6 may have a periodic error of 30 seconds of arc. That just means it will, at any time, be pointing to within 30 seconds of arc of where it should be. If an autoguider brings that down to half a second of arc the mount is now 60x more accurate. That's a lot! Olly

I use a legitimately purchased Ps CS3. I will use it till it will no longer run in any Windows variant I can download. When that runs out I will probably retire! Olly

First point: any deviation from perfect polar alignment will generate field rotation. However, if it amounts to less than half a pixel at the edge of field in the sub length you are using, will you see it? Put it this way, it won't be your biggest problem as an imager! Second point: if it were true that brighter objects needed shorter subs you'd be right. However, my own M42 used 15 minute subs and my M31 used 30 minute subs. Yes, both involved short subs blended in to capture the brightest details but very few objects can be done entirely in short subs. When I say 'very few' I should say that I have yet to encounter one. Olly

Yes! This is the brilliant bit which allows you to guide to a fraction of a pixel, contrary to what might seem reasonable. You don't guide on a star, in reality, you guide on the 'centroid' of a star which is far more accurate. Autoguiding involves an exquisite bit of engineering which can turn a mount's natural error of maybe 30 seconds of arc into an error of maybe 0.5 seconds of arc. And this at a cost of a couple of hundred euros. It sets up a virtuous feedback loop of quite fantastic efficiency. Do it! Olly Edit

We can, can't we? Photoshop has both. Or do you mean that we could offer our audience a certain freedom to choose? Why not? Olly

Hope you like them. I don't have the southern hemisphere one or the Milky Way. Let us know what the MW volume is like. Or maybe I should just buy it. Yeah, I think I should!! Olly