Horsehead Teaser

[MarkS]

A few nights ago I managed to capture nearly 4 hours of data on a night where the seeing was pretty good.  I haven't shot the flats yet, so I can't show you the whole image.  But as a teaser, here's a crop at 100% scale:



Mark

[Carole]

Wow, no noise at that close up view.  Curious why a DSLR camera has misregistration of the star colours, I think you might have explained that before, but I can't remember what the explanation was.

Carole

[MarkS]

Wow, no noise at that close up view.  Curious why a DSLR camera has misregistration of the star colours, I think you might have explained that before, but I can't remember what the explanation was.

Carole

The main effect here is atmospheric dispersion.  It causes a blue fringe to the upper part of the star (relative to the horizon) and a red fringe to the lower part.  I'll need to separate the colour channels to correct this.

Mark

[The Thing]

Hah! Looks just like mine Very smooth and detailed.

If that's 100% size was this using the C11? Interesting about the colour separation, I just thought it was the coma corrector causing it. I'm going to do the Alnitak region again tonight (should be the clearest sky for a long long time) with a different filter and see what I get, and maybe if I have a free week I'll do a Carole and try and add all my versions over the years into to one mega image.

[MarkS]

Yes this was the Sony A7S on the C11 with the Starizona LF 0.72x reducer/flattener

Regarding noise, I have been using a new trick.  Because I use short exposures, I have hundreds of exposures for a typical image.  Hundreds of exposures makes 200% Bayer Drizzle viable.  100% Bayer Drizzle already has finer grained noise than stacking debayered images (which tend to have "blotchy" colour noise). That is why I regard Bayer Drizzle as essential for one-shot-colour images, even if it gives no increase in resolution.  Using 200% Bayer Drizzle gives a noise structure that is very finely grained:



So the next thing I then do is to import into Photoshop CC and open the ACR Filter to apply colour and luminance noise reduction which seems to works more effectively than any other noise reduction I've ever used:



By the time I shrink the image back to 100% scale it is almost noise free.

Mark

[Carole]

Is there a Mono equivalent to Bayer drizzle I wonder?

Though having said that I doubt my PC could handle it.

if I have a free week I'll do a Carole and try and add all my versions over the years into to one mega image.

Way to go, it's helped me out on a number of occasions, especially when I can't get all the data I need in one go, or over several nights.

Carole

[NoelC]

Lovely horsehead.
Thanks for the noise tips.

Noel

[MarkS]

Is there a Mono equivalent to Bayer drizzle I wonder?

Yes, of course, it's called Drizzle.  With a mono camera, I think 30 or more dithered images would give an excellent 200% result.

Mark

[Carole]

Yes, of course, it's called Drizzle.

Ah yes, I remember the name now.  Never used it, though am still dubious whether my Desktop will be able to cope with it.  Also I need to take a look at Astroart and see if it's an option.

Thanks

Carole

[Carole]

Astroart doesn't seem to have a drizzle facility at least on AA5.  So I tried DSS 2 x drizzle and 3 x drizzle on the same data and was getting less noisy results on the Astroart stack. 

Oh well, I tried.

Carole

[RobertM]

Is there a Mono equivalent to Bayer drizzle I wonder?

Yes, of course, it's called Drizzle.  With a mono camera, I think 30 or more dithered images would give an excellent 200% result.

Mark

That looks like a great noise free result, I'll have to try that drizzle on my mono images especially as I take hundreds of short exposures.

Am looking to seeing the final image and especially how you've got on with Alnitak, it should be a stunner.

Robert