[Placidus (Mike and Trish)]

Originally Posted by Paul Haese

That's nice Mike and Trish. Lovely star colours and huge image scale. The galaxy colour is lovely and warm.

Thanks muchly, Paul.

Originally Posted by ericwbenson

Hi M&T,
The semi-random red blotches in the light frames could be RBI. A new 16803 camera might not help (or could be worse!). Large dithering steps is really the best approach (i.e. I am using 20 pixels in ACP, sometimes need even more with the Focus Max left over ghost donut).

If you are seeing them in the darks, are you doing darks right after lights?
That would be the worst case for injected RBI into the darks. The camera should be warmed up and then cooled back down (this empties out the RBI sites) before doing darks after lights.

Best,
EB

Thanks muchly for the thoughts, Eric. I understand the ghosting issue, having carefully read through the physics and also spoken with the manufacturers. I try to focus on a pretty faint star (eg mag 10 for Lum). An original synch shot is also a great way of getting a nice after-image. At -30 deg, takes about 3 1hr subs to disappear. But quite independently of ghost images, the camera can also "imagine" little blobs which come and go in quite a different manner to ghosting. I've chosen not to go down the infrared pre-flash route. NASA advises that unless you cool the camera to something like -70C, the pre-flash hugely increases the noise. I found that to be true. Consequently pre-flash is only the go if you need it for quantitative astrophotometry and you can go very very cold. So, as you rightly point out, the best defence is strong dithering. I've been lazily relying on a not-so-perfect re-centre after focusing to do the dithering for me. Trouble is, either with winter or with wearing in of gears, the re-centering has been getting annoyingly better! I'm going to have to write in an explicit dither. (I do all my own scope control electronics, firmware, and software).

Originally Posted by Stevec35

An extremely worthy NGC4945 guys!

Steve

Thanks, Steve!

Originally Posted by gregbradley

A very nice 4945 Mike. One of your best. I couldn't see any red spots but I agree it could be RBI. Your camera has RBI preflash so you try that out.

Although I thought RBI fades out after several subs. High cooling slows down its fade out. But you would need new darks with RBI on as well as the noise will be different. Its worth a try to see if this helps it.

Greg.

Thanks muchly, Greg. As I mentioned to Eric, I'm not keen on infrared pre-flash. I think stronger dithering is the way to go.

Elsewhere you gently and kindly drew my attention to a green gradient. Had a go at fixing that, and it does improve the image. Many thanks. In addition, I think we need to get some more RGB (well dithered !!!) at next new moon.

Originally Posted by multiweb

The oompa loompa galaxy. Very cool shot.

Cheers, Marc!

Originally Posted by RickS

Very nice work on this strangely coloured galaxy, M&T. You've made it quite a bit more interesting than some of the drab versions I've seen. Some little gems in the FOV too.

Cheers,
Rick.

Thanks, Rick. I'm feeling anxious now. Had a few goes at reprocessing the image, adding in another 4 hrs of Lum, and am struggling to reliably reproduce this version. Coming out more contrasty and less warm. That will learn me to keep good notes.

Originally Posted by PRejto

Wow, beautiful image! I love the richness of colour.

Peter

Thanks, Peter.

Originally Posted by alpal

Hi Mike & Trish,
what a beautiful image.
It made me have a look at the Chart32 image:
http://www.chart32.de/component/k2/6-galaxies/ngc-4945

cheers
Allan

Oh, wow! That image is astonishing. Their scope is only slightly larger. They must be sacrificing something on an altar at midnight. Thanks for showing us. Awesome.

Thanks again to all,
Mike and Trish