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Why all the green….?


Stuart1971
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23 minutes ago, Stuart1971 said:

Ok so same image but different issue, this is the final calibrated image with darks and flats, but as you can see still not that good and the stars are very big, and if you zoom in they are also elongated across the whole image pretty evenly, so I thought as I used 5 min subs unguided, maybe it’s a bit of drift…BUT over the 5.5 hours IMabel for, the Nebula never moved at all from the centre of the frame, so if it was drift surely it would have….it was exactly where it was on the firs frame, with drift I would have expected it to have moved quite a way up of down depending on the drift direction…

There is something called periodic error and that causes drift like elongation of the stars - while object stays relatively stationary.

RA_vs_DEC.gif

For example, in above image you can see two types of drift - right to left is DEC drift - due to poor polar alignment, but up/down drift is due to periodic error. On average stars stay at the same "height" although they jump up and down. On some subs stars get elongated because of that. Longer the sub - more elongation you will see. With 5 minute subs - odds are that every sub will show elongation since worm period is often order of 8-10 minutes and 5 minutes would be roughly half of period (so either up or down part :D).

Cures: PEC or guiding.

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5 minutes ago, vlaiv said:

There is something called periodic error and that causes drift like elongation of the stars - while object stays relatively stationary.

RA_vs_DEC.gif

For example, in above image you can see two types of drift - right to left is DEC drift - due to poor polar alignment, but up/down drift is due to periodic error. On average stars stay at the same "height" although they jump up and down. On some subs stars get elongated because of that. Longer the sub - more elongation you will see. With 5 minute subs - odds are that every sub will show elongation since worm period is often order of 8-10 minutes and 5 minutes would be roughly half of period (so either up or down part :D).

Cures: PEC or guiding.

Thanks….Again…😄

SO my PA is good as there is not right to left drift, which I am happy about as I did spend some time on that, so it’s the inaccuracies of the worm wheel and gear, so guiding is my next thing to get sorted….👍🏼

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4 minutes ago, Stuart1971 said:

Thanks….Again…😄

SO my PA is good as there is not right to left drift, which I am happy about as I did spend some time on that, so it’s the inaccuracies of the worm wheel and gear, so guiding is my next thing to get sorted….👍🏼

Yes, guiding is rather simple thing once you have it all sorted and it becomes part of the routine. You can also use it to dither between subs which is another benefit.

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7 minutes ago, vlaiv said:

Yes, guiding is rather simple thing once you have it all sorted and it becomes part of the routine. You can also use it to dither between subs which is another benefit.

Do you think my pixel scale could be any factor in the larger stars too, as my camera has 7.8 micron pixels with an 450mm scope…gives around 3.9 arc seconds per pixel I think….? 🤔

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3 minutes ago, Stuart1971 said:

Do you think my pixel scale could be any factor in the larger stars too, as my camera has 7.8 micron pixels with an 450mm scope…gives around 3.9 arc seconds per pixel I think….? 🤔

Don't think so.

Large pixels usually make stars smaller.

I think you missed a bit of focus there and guiding will help.

80mm aperture with 4"/px is capable of this sort of sharpness:

image.png.777f7468b978f01a52c2cb9e4cc49532.png

Focus, atmosphere and tracking all play a part and you need to sort out all that is up to you so (focus and tracking / guiding) - and hope for good conditions in atmosphere.

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1 hour ago, Stuart1971 said:

Do you think my pixel scale could be any factor in the larger stars too, as my camera has 7.8 micron pixels with an 450mm scope…gives around 3.9 arc seconds per pixel I think….? 🤔

The combination of Kodak 11 meg chip and Takahashi FSQ106 probably has more APODS than any other single pairing. It works at 3.5 arcsecs per pixel.

You're fine.

Olly

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