M81 Ursa Major

[Fay]

10x300secs with SX & ED80. 0.8 FR/Flattener, cls filter.

I did rgb of this, but cannot process it properly, need more practice. It was a bit smokey around my way & perhaps I could have done with more subs.

[Daniel]

Wow, that's really nice, Had a go at capturing M81 myself a few nights ago and was quite happy to see some spiral arms, but i didn't get nearly the amount of definition you have there!

[Fay]

It could be better, Daniel, the background is not too good, not sure why.

[Daniel]

Im guessing you get less light polution around your area, but Im wondering how much your CLS filter is cancelling out, Im using a UHC-S filter right now, would i be better off with a CLS filter instead?

[JohnP]

Can you show us the image you are getting Daniel...? John

[Daniel]

Hi John, here's my M81 (and M82) you can see the spiral arms a bit, but no way near the definition that Fay gets, One thing i was wondering is if it's better to under expose and take many shots to stack (like with this image which is about 60 20s ISO 1600 images) or if i should try going for longer exposures and try to process the light polution out?

Anyway, here's my attempt

[Ian]

No easy answer to that one Daniel. It's all about understanding the noise you have and how to minimise it. Generally longer exposures are better than short.

I would say though that you would need to improve your tracking to get longer exposures than that. You are just starting to get some trailing, and that will kill a lot of definition as you're smearing the image across several pixels.

I reckon you might be able to get more out of yours with harder processing. It'll go ugly, but there's more detail there to see.

You're also still getting a little coma around the bottom right hand corner, unfortunately, that's where the galaxy is. Your scope is much more collimated than it was last time though

M82 looks excellent, possibly because the details are higher contrast. I'd crop it out and stick that bit in the gallery.

[Mike]

Fay,

I am sure that more detail could be pulled out of yours with some careful processing.

[Daniel]

Your right, it definetly gets ugly once I start pushing for more detail, should be taking delivery of my guide scope on friday, so hopefully I'll be able to expose a lot longer, though my problem seems to lie mostly with light pollution, any more than 30s and I seem to get a hell of a lot of blue/white coming onto the shot, or a lot of red if i don't use the UHC-S filter, also, I was wondering about the photoshop tools you use, are there any other killer tools other than Levels and Curves for processing astro-photo's?

[JohnP]

Hi Daniel,

That's not too bad. You need to be careful because you are trying to compare images from general photography type DSLR's & dedicated CCD imaging camera's with -20degC cooling - imaging with the two of them is a lot different. Still I think the M82 looks great & with more & longer exposures (guiding) M81 would also be great.

Cheers,  John

[Daniel]

Ahhhh, Didn't realise it was a CCD image, although I've seen some great DSLR images too, Im guessing once I've got the autoguider i'll be able to try for longer exposures at lower ISO's

[Rocket Pooch]

Nice images but that galaxy is notoriously difficult to get the spiral arm details out, Fay it looks like filter light leak on your image, either than of you have stretched the histogram a little too much.

[Fay]

MIke the background of M81 looks uneven. I have looked at the individual subs but nothing is obvious, I did RGB but was not very good at the processing. I will have another go

[Fay]

Chris, I was careful not to clip the histogram. What is filter leak? From the top right hand corner there seems to be diagonal lines.

Fay