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M31 - not helped by poor focussing


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Last night was my first trip out with the 100mm lens on the canon. My first problem was focussing, and (as you can see from the result below) this was not entirely successful.

I could not figure out why APT was not playing-ball. So I went into EOSutils and used the moon to achieve 'focus'. Although the moon is great for focussing at longer focal lengths, I don't think it was the best way to do it when, even magnified, it barely filled the screen. Anyway, back to APT to take the pictures. At this point, I discovered something about APT: the preview screen works a lot better if it is not set to 'off' :iamwithstupid:. At this point, I should have refocussed, but didn't :iamwithstupid:2 .

Right, set up program: ISO 800, f/4, 300s *10 (unguided). Throughout the image-taking process, I checked each sub as it appeared, using virtual magnifying glass, and all the stars looked pin-sharp. I guess I just wasn't applying 'enough' magnification. Live and learn. The cloud rolled in during sub #10, so I only stacked the first 9 - 45 mins - not really enough.

I was dithering between frames, so I would not have to do any darks. The only thing I can think is that the amp-glow covers such a large area that, despite using a kappa-sigma process (2.00 5 iterations) in DSS, the noise was so general in that corner that the processor could not see it was staying in the same place. Hopefully, this problem will solve itself once the 1600 arrives.

I have applied all of my (admittedly meagre) arsenal of processing tools on this image, and despite the obvious inadequacies of the full-size image, I think that the reduced image is the best M31 I have ever managed to produce [which is not necessarily saying a great deal], so that is a positive. And despite the comments made above, I am actually quite encouraged with my first foray into 300s-sub territory.

I did take some flats (which I didn't use), but that is another story and another thread.




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I fear you are right, that's another hour, which was exactly what I was trying to avoid by dithering.

At least the canon seems to be consistant ... each set of 10*300s subs I have taken so far has had the first two being taken at 20°C and the remaining 8 being taken at 21°C (at least, those were the figures given in the APT log window). If the 'heat' being supplied by the camera is overwhelming the ambient temperature (which would explain why each set has followed the same pattern), then maybe that is the result I would get taking a set during the day (as long as I don't take them in direct sunlight). Might be worth giving it a go.

Of course, the best thing to do will be to start using the new ASI1600MM-cooled, but I have to get the power supply for that sorted first ... and figure out how it all fits together and works without ANY instructions. ZWO seems to be notorious for that!


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