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Altais

30 hours of M51

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M51 is nicely positioned in the sky these days, so I've spent quite a lot of time imaging it lately. My previous (and first) attempt at M51 was four years ago. At the time I was struggling a lot with getting decent guiding, and had to discard most of the data. With my newly acquired iOptron CEM60 this is basically no longer an issue, so I wanted to see how much I could improve upon the old result by adding a lot of integration time. So here what I have obtained from a bit less than 30 hours of integration time:

M51.thumb.png.6d9dc314b49d00c1cad1d12de876b0cb.png

For comparison, here is the result I got back in 2015, which consists of 1.1 hours of integration time (under very good conditions):

M51_old.thumb.png.7ab6edc21c5d382467e2204132d5991f.png

Both were captured with a modded Canon EOS 1100D through a SW Explorer 150PDS.

While I'm quite happy with the new result, It looks like I'm starting to reach the point of diminishing returns in terms of integration time, considering that much of the improvement probably is due to more accurate guiding as well as better post processing. This actually makes a lot of sense; most of M51 has a high surface brightness, so it is relatively easy to get a decent signal to noise ratio in most parts of the galaxy. More data will still be beneficial for the diffuse outer regions, but for improving details it's probably better to focus on quality over quantity (e.g. only using frames captured during good seeing conditions).

Anyways, feedback and opinions are as always appreciated. :)

Clear skies,
Lars

Edited by Altais
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Nice and detailed Lars, it's rare to see such good images from DSLR's.
Where in Norway are you located?

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7 minutes ago, Xplode said:

Nice and detailed Lars, it's rare to see such good images from DSLR's.
Where in Norway are you located?

Thanks Ole Alexander, much appreciated. :)

I live a bit north of Lillestrøm (Lindeberg i Sørum). It's sufficiently remote that light pollution from the cities is not a big issue (and also we have no street lights), so I get reasonably dark skies.

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Very impressive Lars!

You say 30 hours of integration time, how many frames in total and what exposure time plus ISO for each one, that would be interesting to know.

When I see images like this I think back to the time when you had to use film, with manual guiding. Just imagine if someone had told us back then amateurs would be taking pictures like this in the not so distant future, i'm not sure we would have believed it!

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Sorry but for some reason I think he old one was better - cant put my finger on it.  Thats after looking at them both blown up. Above pictures ,on my screen, look different in size so I guess one goes for the "closer" one normally 🙂

Dam good images :thumbsup:

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7 minutes ago, 7170 said:

Very impressive Lars!

You say 30 hours of integration time, how many frames in total and what exposure time plus ISO for each one, that would be interesting to know.

When I see images like this I think back to the time when you had to use film, with manual guiding. Just imagine if someone had told us back then amateurs would be taking pictures like this in the not so distant future, i'm not sure we would have believed it!

Thank you very much!

It's 274 frames of 6 minutes at ISO800 and 21 frames of 3 minutes at ISO1600 (so actually just 28.45 hours but 30 sounds cooler). The latter is the dataset from 2015 which I reused in the new image in addition to the new data. The reason I changed from ISO1600 to 800 is because I think the additional dynamic range you get with 800 is well worth the slight increase in read noise for this target.

Yeah, it's quite amazing what digital sensors have done for amateur astrophotography. But then it's really humbling to look back at what people were able to achieve without them!

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46 minutes ago, stash_old said:

Sorry but for some reason I think he old one was better - cant put my finger on it.  Thats after looking at them both blown up. Above pictures ,on my screen, look different in size so I guess one goes for the "closer" one normally 🙂

Dam good images :thumbsup:

Thanks! :)

I should probably have cropped the old one to match the new one so they could be compared directly. The old one is quite close to the full FOV of the camera, but with the new one I prefer a closer crop to better reveal the details.

Here is a better comparison of new (first) vs old:

M51.thumb.png.c0deb047ba041357d29433d824e82073.pngM51_old_cropped.thumb.png.d664dbe38ae4b5d2dc30b0f339578fdb.png

 

Edited by Altais
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43 minutes ago, stash_old said:

Sorry but for some reason I think he old one was better - cant put my finger on it.  Thats after looking at them both blown up. Above pictures ,on my screen, look different in size so I guess one goes for the "closer" one normally 🙂

Dam good images :thumbsup:

I tend to agree. Aesthetically I like the wider scale of the older image with the background fuzzies. 

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I agree 1st image , but there is not a lot in it.

Bob.

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