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M81 - DSLR no darks experiment


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It was really good to finally get out on Monday night.

My first plan was to get some 30 second subs of the core of M42 to add to the image on my flickr page, but I found after setting up and polar aligning that I'd placed the scope too close to the fence and couldn't quite see it - doh!

So, went straight for M81 instead.

Not totally happy with this, might have pushed it too far for the amount of data.

Focus looked spot on with the bhatinov, but looking at others' images it doesn't look as sharp so will have to re-check collimation.

13x600s, 1x420s, ISO400

120 Flats

120 Dark Flats

120 Bias

No darks as an experiment because I've read of their dubious worth with a DSLR. I should really get dithering working though!

Stacked in DSS, processed in CS4.

I don't have a coma corrector so left the cigar for another night.

Rest of equipment as in signature.

Comments appreciated as it's about time I started improving!

post-12649-0-21274100-1424292101_thumb.j

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Nice image. Well impressed for a dslr. Only thing I'd do is crop in a little tighter, though the wide shot adds context. Interesting to hear the no darks with a dslr idea. Can you explain what dark flats are please. Thanks.

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Thanks Chris.

I'd love to get the coma corrector but I'd also need a low profile focuser to use it, so until I can afford both deep cropping (deeper than this!) will be my best friend :grin:

Edited by Brent
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Nice image. Well impressed for a dslr. Only thing I'd do is crop in a little tighter, though the wide shot adds context. Interesting to hear the no darks with a dslr idea. Can you explain what dark flats are please. Thanks.

Cheers.

I do have a more deeply cropped version, unfortunately it also makes the noise easier to see :grin: . More sub's needed!

A dark flat is the same length exposure as your flat but with the scope capped, it reduces the noise in the flat frames (hopefully!)

Edited by Brent
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great dslr image with nice colours

That looks great. Especially with the 10 minute exposures... I've heard that you don't need both dark flats, and bias... just use one of them. 

Thanks both :smiley:

I've read about not needing both as well John, just thought that because they are so quick to do it can't harm to include them anyway - but then read that you can double subtract the noise  :rolleyes:  Maybe I should do another stack ! :grin:

Anyway, I thought I'd do a big crop, so, the first image below is a straight crop of the image in the OP, no other processing.

The second image is totally re-stacked (using 3x drizzle), and re-processed.

Possibly too big a crop but I was just interested in what might be there.

Was it worth the extra effort? Not sure, but I'm definitely enjoying processing much more since getting more serious with it.

post-12649-0-66076300-1424430915_thumb.j

post-12649-0-67840100-1424431108_thumb.j

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Thanks for explaining dark flats. Love the new cropped image too. You could lend an eternity processing and I'm never really sure what im doing, but experimenting is fun and when it's cloudy out, as it is most nights here in Northumberland it's good to still be busy with images already shot.

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Great work Brent ... some tips to avoid darks.

1.) create an bias master based on ISO and Temp. (changes at 5c)

2.) Take images using dithering (APT has this option, I use it with PHD2)

3.) Set dither on 2 or 3 and then stack on cappa sigma with sigma at 2 or 3.

4.) Get the SW 0.9 comma corrector, it reduces and flattens.

Good luck ... My efforts for comparison and colour matching. 

Bode_M82_265m_15C.png

Edited by Christopher Davenport
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Thanks Geordie mc, and yes, I have a lot of images to go back and re-process :wink:

Christopher, nice image and thanks for the tips. The cc is out of the picture until I can also replace the focuser unfortunately.

I've just been looking into dithering using PHD - I think I will have to do it manually as I can't use APT or BYEOS at the moment (long story, but camera drivers won't work on my laptops version of windows :rolleyes: )

Great work Brent! The biggest problem with no darks is how you then deal with amp glow which i think is in the bottom right of the first image.

Yes indeed, I didn't notice it until I posted it on here :grin:

That crop just needs to be bigger :grin:

For a DSLR,thats a cracking image,cant have been easy,plus your stars are well controlled.

Have no experience with a DSLR,but still recognize a very good effort.

Mick.

Cheers Mick.

Having just processed an M51 from Saturday night I think I've blown the stars here a bit - there's not much colour left in them (loads in the M51 shot, I protected them properly).

Maybe I'll have "just one" more go at re-processing it, lol

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It is very good result and nice image. I have done the same image few days ago with my DSLR. It is interesting to see your result

Thanks :smiley:

I've just had a look and have to say, though, that yours is more detailed (much sharper), has nicer colour control, is smoother and much better processed altogether. :grin:

Out of interest, where does your imaging location rest on the Bortle scale? I'm very interested as the total integration times are very similar.

Edited by Brent
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