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Walking on the Moon

The Pinwheel - M101

brendant

By brendant
in Imaging - Deep Sky

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brendant

brendant

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Had an nice clear spell for a while late on last night, imaged M101 for several hours but not really happy with the result, would have expected more from the subs but it is beyond me to extract it. Will leave it alone for now and try and reprocess at another time - cannot see the wood for the trees at the moment.

3 Hours 43 Min total exposure at ISO800 on the 400D made up of 32 x 6 Min's + 3 x 10 Min's, ED80 guided with the QHY5 - 400mm lens combo.

Brendan

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Tim

Tim

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Nice pic Brendan.

In an article by Jerry Lodriguss (http://www.astropix.com) he mentioned about the best exposure times for dslrs. He recommends iso 1600 or iso 800. By the very nature of dslrs, by increasing the exposure time, even at iso400, you will also be increasing noise due to the warming of the chip.

I found there was a useful ceiling of about 6 mins with a dslr, after that, there seemed to be little extra data captured, but a lot of extra noise. The 400D is a lot 'quieter' than the 350D though I found.

So probably, it would be better to take lots of shorter subs at iso 1600 or 800. With greater numbers of subs, the noise would smooth out better during stacking. And if you could use the dithering technique in maxim, probably make that bit extra difference too.

Recently George took zillions of 30 sec subs of orion, and the result was as good as fewer long exposures. All in all, if I had 2 hours of imaging time, I would rather have 40 x 180 secs than 12 x 600 secs.

Thanks for posting.

TJ

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brendant

brendant

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Thanks again all for the comments.

TJ - Thanks for the info, yes you are right re sub length but the longer you expose for the deeper you can go but yes at some stage you get to the state of diminishing returns and you are gathering more noise than signal. Interesting to know wheather 20 x 3 Min's @ ISO800 is better than 20 x 6 Min's @ ISO400, notwithstanding the longer exposure time but would it be worth it for less noise ?, Wish I knew the answer, both Christian Buill and Jerry Lodriguss recommend ISO400-800 for most Canons. As with most things it is never straightforward, as local conditions will always play a part, you may well reach the sky fog limit first in any case, and in this case I would say that more shorter exposures might well have yielded a better result. That's the thing about this game, few absolute rules and every night is a new learning experience.

Brendan

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philj

philj

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Thats a nice image you should be well pleased with it.

3hours plus of clear skies, :( I would kill for that, There hasnt been more than 2 hours clear here for over a month now, even then its been blowing a gale.

Phil

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brendant

brendant

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Thanks again all for the comments.

Phil, takes some serious dedication though (I like my bed), only noticed the clouds clearing at 11.00pm, setup and imaged till 3.30am, at least it was a Saturday night, would have been impossible during the week.

Brendan

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Tim

Tim

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Thats the thing Brendan, no two nights are the same, condition wise, and even if they were, they'd be so far apart in this damned country that you'd forget what you were testing anyways........

So we have to take what we can, when we can, as you did here, and isnt it a good feeling when the compromise you decide upon yields such good results.

As for the mixing of the different length subs Billy, do you just lump them all in together? That was what I used to do, but a recent comment by Dennis (Roundycat) makes me think otherwise, that its better to stack all the same length ones together, use sigma reject stacking, then stack the results together using average combine. At least, I THINK that's what he said.....

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Luke

Luke

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Well done Brendan, I'd love to be able to take some images like this but I'm using a non-slr digital camera for the mo with max 30 seconds exposure, so I've only managed smudges so far!

Galaxies like this look so awesome to me! I hope I can get an slr later this year and head this way! Very inspiring to think these can be captured.

I was reading that there are a whole heap of galaxies in I think Virgo? Can't wait to eventually get an slr and have a crack at them! :(

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Darth Takahashi

Darth Takahashi

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That's a marathon 3H 42M. M101 is a difficult object to locate, low surface brightness, then it needs lot's and lot's of time. There are just no short cuts in astrophotography.

Excellent job, I'm sure you will wring the last photons out of the image later, however, it already looks good to me.

Neil.

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brendant

brendant

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Thanks Les and Neil, hoping to add more data to this one, pity about the full moon at the moment, nice clear skies though, it's a late one for me as does not clear the trees till about 11.30 pm, could do with another 3 hours.

Brendan

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