M101

[Darth Takahashi]

Here is my first attempt at M101, this has a very low surface brightness and is difficult to image. Still needs a lot more data but I think its getting there.

As usual, colour balance is a struggle with these images and I seem to have been fighting on two fronts with the Green and blue channels respectively.

I hope you like it.

[shaunster]

Nice detail in there of a difficult target, do you have details of exposure times etc?

Maybe the stars have been over sharpened during processing?

[Darth Takahashi]

Thats actually a difficult question;

The reason is that I changed the exposure times on the second run:

I started with my normal 5mins subs for everything;

7x 5mins RGB

10x 5mins Lums

Yesterday night I changed the lums to 10mins and ran another 18 of them, the RGB componets were left at 5mins since they are binned 2x2 but this might have been a mistake!!!

So in total I have about 13x5mins RGB and 230mins in Lums so far.

I hope that answers your question?

My biggest issue is that I need a consistent image processing routine for Pixinsight since I'm doing more and more with it and learning all the time!!!

[MartinB]

Central detail looking good Neil. Just need more data now for the outer bits.

If you are combining luminence subs of different lengths it is important that the software is able to "normalise" the subs i.e. it should be able to measure the brightness of the dark areas i.e. background sky and mid levels so that it can factor in the correction required for the different length subs. If this isn't done efficiently than you can end up adding noise to your combined image. Maxim v5 does this automatically but you can tweak the settings, CCD stack gives a lot more manual control.

Just had a look at your M81/82 as well which is a stunner.

[Darth Takahashi]

Thanks Martin I hadn't considered that point. I'll check that but at the moment the simple fact is that I don't have a good enough signal to noise ratio for the colour channels so tonight I'm only doing RGB's.

If the weather holds I'll try to get some H Alpha as well.

I have 4 hours of RGB planned at 10 mins / sub.

The red channel is the best, followed by the blue then green but a lot of noise is coming from these components and I'm being heavy handed in PI with background noise control etc...

[peter shah]

tricky one this......you have done a fine job on it so far....Martin is spot on when combining.....you also have a very slight green cast surprising what a slight tweak on the colour balance can do....well at least on my monitor.

[Darth Takahashi]

Here is the final M101 well at least for now. This image has been a huge undertaking with some 8+ hours of image data contributing to the final image that you see here below. I when back to this one and added some more colour data, since the noise in the RGB channels was too high.

I hope you like it. Its the best that I can do from my location here in the Netherlands!

[davew]

If you wish to look at colour balance, a technique I've read about is similar to G2V in that it looks at the central core. That's as good as white on the majority of Galaxies.

A thought.

Dave.

[Darth Takahashi]

If you wish to look at colour balance, a technique I've read about is similar to G2V in that it looks at the central core. That's as good as white on the majority of Galaxies.

A thought.

Dave.

Agreed, colour balance is a trick one! I've tried the G2V calibration in the past and it wasn't so successful for me. Here is a more neutral image with less blues etc... You might prefer this version? The second one is slightly de-saturated which helps to whiten the galaxy arms etc...

The problem with colour balance is that its effected by so many variables;

1. Seeing and atmospheric extinction

2. Camera sensitivity

3. Filter bias

4. Processing technique and own bias?

I try to look the images up in the books that I own to give myself a good reference, lots of the cores appear yellow to me? Not white but I'm interested in learning about the technique? Please provide a link to it?

[davew]

Deep Sky Colors - Astrophotography by Rogelio Bernal Andreo

He has written a small app to help with RGB balance using G2V or Galaxy Cores.

I don't have any specific links. I just read and forget

Dave.

[Darth Takahashi]

Deep Sky Colors - Astrophotography by Rogelio Bernal Andreo

He has written a small app to help with RGB balance using G2V or Galaxy Cores.

I don't have any specific links. I just read and forget

Dave.

Unfortunately its only for WindoZ users which is a pity!

I do all my post image processing with a MAC and hence use PixInsight for most tasks and finalize with PhotoShop like most.

In fact, if I cold free myself from the EVIL of WindoZ completely I would but most of my control and capture takes place under WindoZ

Sorry for the WindoZ rant...