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M1 Crab nebula - failure


LouisJB
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I tried to get some data for this Sunday night but now I come to stack and process it I realise it's a bit of a failure. Too bad even to post up.

Is this a hard object to image - with my modest equipment, should I give up or maybe persevere? Perhaps this is the domain of the high focal length SCT or a tiny chip size is required.

I was very small in my image, I guess not helped by my APS-C DSLR chip-size. I couldn't locate it at all with bins, not sure if that says something about my local sky at the time. Compared to say M66 which appeared after 3 3min subs on the same night (and was low in the sky) it seemed really to not be very easy as a target at all.

Perhaps I had wrong expectations. Being so famous and with it being the 1st Messier I suppose I thought it would be relatively easy...

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It isn't very bright and certainly Messier's catalogue isn't ranked in order of best to worst. I found it took much more time than I expected to get something, and I actually gave up when using a DSLR on my 150P. I revisited it with a 285 chip CCD and a 250PX and it was a much better image scale. Visually, I have seen it with an ST80 but only because I knew exactly where to look.

If you give it enough time, in long enough exposures it actually works quite well in widefield though, so if you have a good start on it, keep plugging away and it will come good in the end.

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This one is on my list before it dissapears again around March. The longest usable FL scope that I have is the SW 100ED DS PRO and even with a 0.85 FF/FR it is at f7.6  so it is rather slow but I might just use the Atik  with it and use 600s subs  if this horrible weather permits. Certainly not an easy object to image due to its small size and it is also quite dim. For inspiration have a look at Tim's capture.

http://stargazerslounge.com/topic/171946-m1-crab-nebula-in-narrowband-and-broadband-pushing-the-limits-of-mount-camera-and-sky/

Regards,

A.G

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Thanks for the replies.

Tim's image is amazing. I notice that was with a native 2800mm focal length 11" tube and a tiny CCD sensor, so giving a completely different image scale to what I can achieve with what I have (1000mm and relatively massive APS-C). So this probably isn't a natural target for my current setup.

I might have another go sometime though, something did come out but I think there were guiding troubles and my ST80 did fog up a few times :s It's a good target to aspire to, but maybe it's a few levels above what I can achieve today. Lovely object though. Who knows, maybe I'll end up with a similar tube one day but I'll keep practicing for now.

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your setup is fine for getting M1. The main problem is that there is a lot of Ha emission from this object which is hard to detect on the DSLR chip unless its been modified. your trick is to get as much data as possible (total exposure time) then it will come out in the processing. Persevere!

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Thanks for the replies.

Tim's image is amazing. I notice that was with a native 2800mm focal length 11" tube and a tiny CCD sensor, so giving a completely different image scale to what I can achieve with what I have (1000mm and relatively massive APS-C). So this probably isn't a natural target for my current setup.

I might have another go sometime though, something did come out but I think there were guiding troubles and my ST80 did fog up a few times :s It's a good target to aspire to, but maybe it's a few levels above what I can achieve today. Lovely object though. Who knows, maybe I'll end up with a similar tube one day but I'll keep practicing for now.

Tim used a very high sensitivity CCD and imaged it in RGB rather than OSC so yes it is possible with a DSLR but within reasonable expectations.

Regards,

A.G

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that's pretty good, with an ED80 and DSLR? That gives me some hope. How many subs and what length did you use to get that image?

It was 78minutes@ISO800......various sub lengths, ranging from 3minutes to 15min, was testing my guiding.

I do need to go back and process properly now I have software to do it.

Edited by wxsatuser
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its certainly not the brightest messier, but it is probably the most historic. you should have no problems getting a decent image with the equipment you are using. just plenty of data and patience, i found it a quite rewarding object to image with my 200PDS/DSLR350d 

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Thanks everyone. This is essentially what I did get

b34468bb-052d-43d9-a706-b677cc657602.jpg

Not exactly great :s

but I think that's only a small number of subs as some were blurred (guiding troubles) - so probably about 15mins data or less. Perhaps with an hour + of decent subs something more defined might start to appear.

Also has the gradient problem but it's not worth messing with such a low-quality image. Live and learn, will rerty it when the time is right.

Maybe the main problem was expectation mis-match, thought this would be bright and easy, in fact it's small and dim, meaning you need much more exposure time than I had attempted to get away with. Also hopefully will have guiding gremlins ironed out over next session or two.

This thing about taking various sub-lengths, is there any way to know what might work or is it experience/guesswork/trial and error?

thanks again, all good advice and information.

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I was only messing about with sub lengths because I wanted to see how long I could guide for.

The longest sub was 900secs and various others ranging from 180, 240, 300 and 600secs.

The longest sub will depend on how bright your sky is on a particular night.

With a Canon camera the sub is about right when the histogram is somewhere

in the range of 20>40%, I normally aim for at least 20%.

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