Ouroboros

I decided to have a look at some of my subs to see how many pixels they shift between subsequent shots. The was data obtained with a 910mm FL main scope and 176mm FL guide scope. Focal lengths determined by the ASIair. Anyway there's a x5.2 multiplier between the two. The pixel sizes between the main and guide cam are identical. I had set the dither to 5. Presumably that's +/-5. I'm not sure whether the 5 pixel dither referred to is measured along the x and y axes, or whether along the hypotenuse. Anyway it doesn't matter a lot because of the large difference in focal lengths. I do get some odd measured dither values ie more than 5 but much less that 5 times 5. I think the maximum dither was 13.5. But most were less than 5 along the hypotenuse. The over size ones are probably down to a shift in pointing or something. Odd because my stars were (mostly) round. Anyway, I think this confirms what ZWO told @Jim Smith ie dither is main camera pixels.

Oh, yes. Sorry. You did say.

I really like that, @kirkster501. I like the way the galaxy core is large and misty. Quite often the core of M31 looks too small and intense in images. I also like the subtle saturation in the white bits of the galaxy and the additional ‘highlights’ of colour on the disk’s edge. That’s coming on nicely. Perhaps for my taste the yellow stars are a tad too yellow, but it’s all down to personal taste. I don’t know whether you find this but if I process an image for too long I can’t assess it anymore. I have to leave it and come back to see it (almost) afresh.

I know where everything is. It’s here somewhere …. errr …. errr ….

Nice. Lots of detail in the Ha. What were the imaging details, telescope etc?

Yes, good point. I’ve never bothered to measure it. I set it at 5 pixels. The maximum is 10 isn’t it? Can’t remember. Anyway as long as I’ve see it shift a bit between subs I have accepted it as working OK. I am also uncertain just how it important it is to dither with a CMOS camera in my case given that I use a master dark. I started using dither back when I used a DSLR to avoid having to take darks after imaging.

Thanks for doing that.

Oh, @FLO … and something I should have asked earlier …. how is an ASIair best attached to the handle? It looks like direct connection is not possible unless the slots in the handle happen to be separated by 20mm - the distance between the threaded holes on the underside of the ASIair.

@FLO. Brilliant! What lovely people you are! Thanks.

How does the filter holder work? I can’t find any pictures or videos of that. That’s mounted filters presumably?

I feel I ‘know’ it’s guide cam pixels from knowledge lost in the mists of time. You have to multiply by the focal length of the main scope divided by the FL of the guide scope to get the dithered distance on the main camera. That assumes both camera pixels are identical in size. If not you have to further multiply by the ratio of the guide cam pixels to main cam.

Absolutely superb.

Hello @Thalestris24. Sorry to hear you’re selling up. I think it’s a good suggestion to approach a local astronomy society. My local As group helped someone out in similar circumstances. I wish you well for the future and hope you continue to drop in here from time to time.

Getting back to the subject of this thread …. Odd though this may sound something I increasingly find if anything more off-putting than the weather is the extraordinarily high standard that an elite group of ‘amateur’ imagers are now attaining. When I started AP amateur astronomers were making do with somewhat less sophisticated equipment and processing. It felt like a more level playing field. It doesn’t feel so much like that to me anymore.

I’ll give it a go. Looks like there’s going to be plenty of opportunity to test it this week having just watched to 5 day forecast on BBC.

Looks similar to … https://www.ventusky.com/?p=54.0;0.7;5&l=radar And https://en.sat24.com/en/gb/rainTMC

OK. Yes, I use websites that show rain radar. If there’s some heading my way I go and cover the scope. Someone should develop an App that uses the rain radar data to sound an alarm if rain is within a certain distance and headed towards your post code.

Do you have a rain alarm?

Personally I find that an interest in visual astronomy helps. Let’s face it there are only a few nights on which clear skies, opportunity and enthusiasm align to make imaging really worthwhile. But there are probably more nights on which patches of clear between the clouds coincide with a half hour or so opportunity to get out there with the mark 1 eyeball and a pair of bins. On even clearer nights, but not “imaging clear”, or perhaps rain threatens in an hour or two, I like to get the telescope out. Recently I have found that using the ASIair to control the mount, and the guide scope to plate solve and point the telescope dead centre at the object of interest, has been a great boost to my enthusiasm for visual astronomy. GOTO is good, but not as good as GOTO plus plate-solving. Oh, and you can do a bit of EAA too, which is imaging of a sort.

There should be something equivalent to a sort “Drake equation” for astro imagers shouldn’t there? Number of imaging nights per year = 365 x Nc x No x Nm x Nd Possible coefficients might include: Nc = The fraction of clear nights per year No = The fraction of nights on which no conflicting factors prevent imaging Nm = The fraction of nights on which there is no moon (if that’s relevant) Nd = The fraction of nights it is sufficiently dark for imaging etc Feel free to suggest other coefficients relevant to you. Since I only seem to get a handful of imaging nights per year I can only speculate that some of my coefficients are quite small fractions - especially No. Having a permanent set up must make all the difference though.

You know those nights when it’s cloudy but there are dark patches with stars between them? Well, it’s like that here in Cornwall tonight. What with that and intermittent rain it’s not worth getting the scope out. So, I’ve just come in from a stroll round the garden with the bins trying to spot a few old favourites. Ursa Major and Minor, Hercules and the M13 cluster, Vega in Lyra, Altair, the coat hanger cluster, Saturn, Aquarius. I think I could just see M31 with averted vision. Very clear through bins though. The Triangulum Galaxy (bins), Cassiopeia, Caroline’s Rose Cluster (bins), the double cluster in Perseus. Jupiter and it’s four brightest moons was visible for a moment before disappearing behind cloud.

This is an OSC image of Crescent Nebula NGC 6888 taken with my ZWO ASI2600 attached to my old Skywatcher 200P. Its 61 x 120s exposures, just over 2 hours, captured on the 13/14 September in Cornwall. Bortle 3/4 sky. Processed in Pixinsight. I was hoping for more data, but two hours was all I got before clouds piled in, and there’s been no opportunity here for astrophotography since. I haven’t used my 200P for imaging for a couple of years at least now. I also dug out a coma corrector I’d bought years ago but which produced unsightly flaring of bright stars when I tried to image Pleiades. However, here it seems to have done a good job - presumably because the stars are less bright. The blue-green oxygen green was difficult to pull up, but it is there. Anyway, thanks for looking.

Oooh, very tempting. Any reviews or test reports?

My first one. It’s been downhill ever since.

Wow. That is amazing. Like a breaking wave of surf! Well done, Lee. You just seem to get better and better.