Thanks again for the helpful replies.
Janes TX I really like your NGC3638 and M101 images, they are impressive and sharp. Regarding M101 I like the prominent red Ha cluster regions in the spirals but in my M101 image even after 14.5 hrs subs the red Ha regions are not striking. I have noticed this with other galaxy comparisons.
Apart from more detailed images I am particularly interested in bringing out out these Ha regions that are proving difficult to see clearly at present. Would an Ha filter do the job?
Also my ZWO ASI 2600MC has an IR block but no UV block. Should I have a UV block filter permanently in place as without it I understand I can have bloated stars as the UV light focusses in a different plane to the visible? My stars are not as small as I would like despite careful focussing and a main mirror fan which I recently fitted though it seems to make FHMW figures greater, expelling air, maybe less so blowing up the tube.
I only started astrophotography a year ago so these are early days..
I have an example of my M101 image on my webpage at www.moorefam.plus.com. This will show what I mean about the Ha regions not being prominent.
In regards to the asi2600mc, yes you want to block both UV and IR. I don't have a 2600mc myself but I was under the impression that it blocked both with its cover. The asi533 which I have doesn't block either and I use a luminance filter for that purpose.
For the Ha regions, yes you need an Ha filter. Actually, if you have something like the L-Extreme or triad you can use that instead of an Ha filter.
The procedure is pretty straight forward. I use Pixinsight so I can explain the basic steps in PI.
- Assuming you use something like the L-Extreme for Ha, split the L-extreme data into separate RGB channels. Label the red as Ha and discard the green and blue.
- With your broadband data.. also split it out into separate RGB channels.
- Then use pixel math to combine the Ha and Red channel. Lately Ive been using 40% Ha and 60% Red.
- Then recombine your RGB data with the lrgb combination tool.. using the combined Red+Ha image in the red channel
Sometimes the Ha is too strong. You can use the Ha frame to create a mask to isolate the Ha regions when you continue your post processing.
I used the above method with this shot of M33, taken with my 70mm refractor (sv70t), the asi533 and the L-Extreme for the Ha data:
I really should post a video on how I do this. On my youtube channel I posted a video comparing my previous attempts at M101 with this latest attempt. It's fun to see the progression you make after a couple years of experience.
btw.. your M51 shot looks fantastic!
Edited by JamesTX, 04 May 2021 - 11:45 AM.