M16 16x240s ISO 800

[Daniel]

Hi all, as prommissed heres the M16 I took the other night on the 12"SCT, I think the gradient has something to do with the cloud that was present especially at such a low angle.

Im also not sure what the strange "wrinkle like" blotches are, there are dust bunnies but closer up there are also diaganol streaks

Anyway i think it's got a little more detail than the last one, only got just over an hour on this so im looking forward to doing it again with longer subs.

it's not great but here it is

[MarkS]

It looks good Daniel.  That LX200 is certainly showing some good potential.  I don't know what you men by the wrinkle like blotches but the diagonal streaks are an artifact of stacking - I'm assuming that the starfield creeeped along the same diagonals during shooting.  This effect can be substantially reduced by having a good set of temperature matched darks.

[JohnP]

Does look good Daniel.... Maybe a 'tad' too dark - I would lighten up if it was mine Also some of the stars look almost 'hexagonal' in shape - have you any ideas what causes this?

Great result for such a low object though....

John.

[Daniel]

Mark, I've just checked all the angles on the original images and the streaking is indeed in the direction of travel the original files. i took a few darks when shooting this image, but it doesn't seem to have cleared it up, do you know of any stacking options that would help cut this down? Im using DSS right now, though, If you know of any programs that would do a better job I could look into them.

John, I agree, I did a lot of darkening to get rid of some nasty amp glow (does anyone have any tips for getting rid of this?) in the corner, the hexaganol stars may be because of a little over zealous processing that eroded the stars around the edges.

I  got about 25 minutes on bubble nebula last night between clouds but picked up the same diaganol lines albeit slightly less than I got on M16.

Oh, and one other thing I completely forgot to mention, the M16 was taken with half my apeture buried in my garden fence, I'll have to raise the legs on my mount next time I try this.

[MarkS]

Sigma stacking should help certainly help. Try a standard deviation of 2 or even go down to 1 if 2 dosesn't work.

[Daniel]

Hi Mark, I tried sigma stacking with deviation of 1 but no luck, i've now even tried manual alignment and it's still streaked although I don't see these in a stretched single sub.

One thing I have noticed in the subs is that there's quite a bit of chromatic aberation, but not in the same direction of travel as the guiding drifted.

I've also been looking around other boards and it seems this is a common problem, but i havent found a solution yet

[MarkS]

Daniel,

I can't think of much else you can do apart from softening the image or applying some other noise reduction technique.  Mask the stars first to prevent them being softened as well.

You won't see the streaking in a single sub - it only occurs during stacking.  The problem is that some pixels are noisier or brighter than adjacent pixels.  During stacking, these pixels form trails as each successive sub is moved slightly to align the stars.  Darks and flats ought to get rid of most of this effect. but in your case that does not seem to be the case for one reason or another.

I took an image of M16 at DSC on Friday night using the modified EOS 350D on the C11 - 50 minutes worth of 5min subs between clouds.  I'll post it tonight - it'll be an interesting comparison.

Mark

[Daniel]

Ahhh, admitedly I didn't take as many darks as I'd have liked to, I might have another go when i get the chance but match the number of darks to the number of light frames I take.

I'd be very interested to see the M16 from tuesnoad, im guessing from there you didn't need a light polution filter