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pipnina

(M101) First proper image from the 130-PDS & HEQ5. Seems to have been a success :)

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2 hours of 60second subs over two nights (short summer nights are a curse, as are short-lived camera batteries).

I used 70 bias frames and 22 "Sky-flats" (Just pointed the scope near the zenith at about 5/6PM) It seemed to work well enough despite not having a diffusing layer. I think the strongest gradients are not caused by perhaps my flats not being 100% perfect and unresolved AMP glow and dark current. I am worried about my star shapes, howver. Looking to the top left and bottom right they seem elongated, and in the other two corners they seem bloated or squashed (against the motion of drift). Perhaps my coma corrector spacing is out?

I think my focus is getting there, stars are sharper than with my first "dry-run" but I think we have a ways to go with focusing, polar alignment, and possibly "drift alignment" and PEC (which I need to read into!)

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Zooming in on M101, I notice a few bright blue objects in the arms (and just southeast of the galaxy) Are these what would be identifiable as Ha regions in astro moded cameras? My camera has the IR filter in place and so probably blocks 90% of Ha data.

I was fortunate to get two nights of imaging time in a row. Hopefully I can get this luck again when the longer nights draw back in :)

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31 minutes ago, pipnina said:

Looking to the top left and bottom right they seem elongated, and in the other two corners they seem bloated or squashed (against the motion of drift). Perhaps my coma corrector spacing is out?

Eggy stars look to be radiating from the centre so it would indicate spacing, I can never remember if it means it's too close or too far away from the sensor, someone will know.

Nice M101, been working on it myself the last couple of clear nights.

Focus looks OK focusing was tricky up here last night with lot's of gunk floating in the air.

Dave

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It looks like spacing issue, but also there seems to be some tilt - one side has dominant astigmatism. Sort out tilt first (make aberrations look same in each corner) and then home in on correct spacing.

Yes, M101 has HII regions, and some of them can appear blue if your camera is not sensitive enough in Halpha region. Very often HII regions shine in both Halpha and Hbeta, first being much brighter and red, second less bright and bluish - people often view such nebulae with Hbeta filters because eyes are much more sensitive to that wavelength than Halpha.

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10 minutes ago, StargeezerTim said:

Lovely star colour! Lovely image for your first proper go. What camera and iso did you use?

I had to use a very strong noise reduction filter on the chroma, allows me to stretch the colour out without ruining the image. Some fainter but brightly coloured stars have colour "halos" around them as a result however. I don't like noise reduction on luminance as it tends to muddy the image too much. I'm just using my unmoded D3200 at the moment.

9 minutes ago, vlaiv said:

It looks like spacing issue, but also there seems to be some tilt - one side has dominant astigmatism. Sort out tilt first (make aberrations look same in each corner) and then home in on correct spacing.

Yes, M101 has HII regions, and some of them can appear blue if your camera is not sensitive enough in Halpha region. Very often HII regions shine in both Halpha and Hbeta, first being much brighter and red, second less bright and bluish - people often view such nebulae with Hbeta filters because eyes are much more sensitive to that wavelength than Halpha.

Would this be tilt of the items in the focuser or tilt of the secondary? I had thought my secondary alignment was quite good but I'll double check. It may be possible that I merely focused the right astigmatism into better focus as I used a star on the far right of the frame as a focusing reference?

The Ha is interesting. Would this mean other nebulae rich in Ha are likely to show up blueish? Nebulae like barnard's loop and the horse head show up as a deep red in my widefield shots despite the deficiency of the camera.

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