M81 - bit of a mind blank

[steviemac500]

Every time I've imaged this there is always much more of  a blue colour to the galaxy. I tried the photometric calibration this time and I'mnot sure about the results. Granted, I haven't go as many blue exposures as red and green (24 vs 12) and my exposure lengths are 300s. So, would increasing the exposure lengths improve the colour or simply more exposures? I've included a cropped version too. Comments will be very welcomed!

[wimvb]

It.s a lovely view, and I like the setting. You also managed to lift Holmberg (dwarf galaxy below M81) above the background. To fix the colour issue, I think you need to increase the number of blue subs, and check your setup's sensitivity to blue light. As it is, the background in your image has a blue cast, but this can be due to noise. What camera and filters did you use?

[steviemac500]

Thanks Wim. I use a Moravian G2 8300 with Baader RGBs. I’m thinking  the number of subs as well. 

[StargeezerTim]

Did you use any filters? I find that UHC and LP filters have a dramatic effect on reducing blues and yellows.

[steviemac500]

45 minutes ago, StargeezerTim said:

Did you use any filters? I find that UHC and LP filters have a dramatic effect on reducing blues and yellows.

Hi,no, no filters.

[steviemac500]

5 hours ago, wimvb said:

It.s a lovely view, and I like the setting. You also managed to lift Holmberg (dwarf galaxy below M81) above the background. To fix the colour issue, I think you need to increase the number of blue subs, and check your setup's sensitivity to blue light. As it is, the background in your image has a blue cast, but this can be due to noise. What camera and filters did you use?

I thought it had more of a red cast Wim?

[wimvb]

5 hours ago, steviemac500 said:

I thought it had more of a red cast Wim?

 On my mobile phone, the background looks blue. On my computer screen somewhat less. To make sure, I downloaded the image and opened it in PixInsight:

This time PixInsight agrees with me. (It doesn't always  )

If I bring the blue dark point in to align the histograms, the background looks neutral. Was there a difference in galaxy colour before and after noise reduction? The outer regions of M 81 are very "thin" and need a lot of data to get right. That's why I suggested getting more blue.

[steviemac500]

No difference before or after. Soon as the sky clears I’ll grab those extra subs and see what different it makes 

[Rodd]

I find that when you have one filter much less represented in a stack, that color counterintuitively dominates--and you can see the blue in your background--I have been told it has to do with noise.  To fix, Mask out the galaxy and stars and hit the background with SCNR blue--but not at 100%--you will have to trial an error it.  Check your histogram-is the blue much wider but not as high as the others?

 

Rodd