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Orion Nebula with 5 Second Exposures


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This was messing about with a test, I wanted to see if you could get much detail when using lots of short exposures, wasn't sure what would come out.

It was a stack of 450 (!!) x 5 seconds, 38 mins total, through an 80mm refractor.

The mount was level and vaguely pointing north but not polar aligned (I'd been imaging the moon before it was dark!). I was thinking I would try 15 second exposures but I got bad star trails so went for 5 seconds instead. Later in the night when I did polar align, the mount was a fair way out!

I was surprised at how much detail came through considering the very short exposure time. On the slight downside, the image stacking did take quite a lot longer than usual and ate up more storage space and there seems to be a different type of noise than I usually get, some streaks (read noise?).

My feeling is that while you are better off with longer images usually, try lots of short exposures if you are struggling with star trails, you might be surprised at the results! I was anyhow. Hope it's interesting!

In the comparison pic, the left hand side compares one of the 5 second images brightened up to show as much detail as I could get, vs. the final image down the right hand side (the final image also had darks, bias and flats).



Edited by Luke
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That turned out very well Luke. 5 Second subs are too short to register trailing, even at the nebulas low declination, where trails would be at their longest.

The core looks great too, normal long exposures can usually burn it out.

It's a lovely image, and a great example to others who don't have good guiding capabilities. They can accomplish some imaging.:o


Edited by barkis
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I'm well impressed with your test shots and skill in developing to such a beautiful finished image this will help me and many others that are not using guiding yet

My only question is where were these taken ( i assume a dark site ) ?

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That is very good for just 5 seconds per exposure :o

I am wondering if because of bad alignment, would you have re-centre the main subject every now and again or does stacking compensate for a certain amount of movement over a couple of minutes?

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That's really cool.

I was imaging M42 the other night and tried some 5sec exposures to try and avoid saturating the trapezium stars, but I got lots of regular vertical lines on the image. I was wondering if it might be read noise. Is taht what you saw? And did bias frames help remove it?


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Many thanks for the comments!

GrantEb, sorry for missing the camera info, it was a Canon 450D unmodded, ISO 1600, prime focus, using a Baader Neodymium moon and skyglow filter. I don't know really which ISO is best, for me 1600 seems fine if I get enough subs?

Carpman, the sky here is not bad, better than normal, but not super dark. North is pretty good but south has got two nasty lamp posts, I guess we all have!

Billy I did forget to mention that the PC almost blew up LOL! It seemed to go into a deep sleep and threatened to reboot itself just before it finished, which had me trying to revive it in a panic! It made it, phew. I guess if I had quite a few more subs I would try resizing them first as I never seem to be able to use the full res anyway?? I think I may be doing overkill feeding it the full res images? Or does it all help?

Tom I did recenter the target three or four times! It was drifting a bit and I did wonder if deep sky stacker would be okay about it. I had mosaic mode set. As Billy says, some of the edges that didn't get many subs were a bit ropey so they got cropped off quickly! :o

Old eyes, I did have problem with vertical bands too! I don't know if it is because I was fishing around in lower levels than normal or whether that was "read noise"? I've heard that you can get more read noise when doing more, shorter exposure subs, but I have no idea what it is! The vertical bands were only visible I think when dipping into the very lower levels, I wonder if I'd been able to get 15 second shots whether that would have sorted them for me??

Sean I would be ecstastic if this helps someone get an image using short subs, that would really make my day as I've had so much help from others, without giving much back yet!

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You can use the custom rectangle in DSS to only stack the bit of the frame you are interested in....

Also, maybe having a short pause between the exposures should reduce the read noise....

It is still amazing that you've gotten so much detail with those stacks....brilliant work!

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Ahhh I see, it must end up like a stack of papers that have been fanned out ready for scanning (I work in an office lol :o) and the edges get cropped off as they will have less total exposure time.

You learn something new every day thanks to the people on here :(

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