Ngc4945

[Jimbo_Aus (Jim)]

Recently moved to another suburb and this is my 2nd image taken at the new home, unfortunately I'm still stuck in a bortle 6 location. One positive is that I can setup in the backyard instead of the front yard at the previous house.

Image details:
Lum - 181 x 60s
Red - 76 x 60s
Green - 52 x 60s (had to dump quite a few subs due to clouds)
Blue - 73 x 60s
Ha - 8 x 240s (definitely need more Ha data)

Calibrated with 75 x Flats, Flat Darks and Darks, Gain 139, -15deg

Equipment details:
Skywatcher Esprit 100
Saxon AZ-EQ6 GT
ZWO1600mm pro, 290mm mini and OAG
Lakeside Astro Focuser
Astronomik Deepsky RGB, CLS CCD for Lum and 6nm Ha 1.25" Filters
Pegasus Astro USB Hub
Hitec Astro Mount Hub Pro Compact
Optec Flatman light panel for flats
SGP Pro for image acquisition, PHD2 guiding, Sharpcap Pro for PA and Pixinsight for calibration and processing.

[PKay (Peter)]

Hi Jim

Good effort with over 7 hours of data.

When processing, useing a reference image (from Asrobin?) of the same target
gives one something to aim for.

Doing the tutorials for Pixinsight gives us new skills and techniques
that will produce the best result.

Well done

[Jimbo_Aus (Jim)]

Hi Peter,

Thanks, I use astrobin when planning sessions and also for tips on exposure settings with similar setups, definitely helps. Just wish there was something with tips to remove or reduce the microlensing with bright stars which seems to be an inherent issue with the 1600mm.

[PKay (Peter)]

Hi Jim

It just occurred to me that when you combine the different channels,

they should be aligned (registered) first.

Take the Lum image (or any channel) as the reference, and align all the others to it.

Makes sense?

[Sunfish (Ray)]

Maybe the focus is not perfect and varies over the night and between filters particularly lum. I don’t see this problem in my 1600 . Interesting to see the result without the lum and less stretchand see if that filter is the problem.

[Jimbo_Aus (Jim)]

Originally Posted by PKay

Hi Jim

It just occurred to me that when you combine the different channels,

they should be aligned (registered) first.

Take the Lum image (or any channel) as the reference, and align all the others to it.

Makes sense?

Thanks - I use a reference sub which is determined by the SFS function that has the lowest FWHM value and also use a weighted expression to determine the highest weighted SNR and use that as a the reference sub when running image integration. Something I've been doing since reading Warren Keller's Inside Pixinsight book. I also dither during image capture and then use drizzle integration. I never had this problem with my other ZWO camera which is a 183mm pro but that had it's own problems with amp glow.

[Jimbo_Aus (Jim)]

Originally Posted by Sunfish

Maybe the focus is not perfect and varies over the night and between filters particularly lum. I don’t see this problem in my 1600 . Interesting to see the result without the lum and less stretchand see if that filter is the problem.

Thanks Ray - this also happens with SHO imaging and in particular with my OIII filter (Astronomik 6nm 1.25"). I've attached a screenshot from PI of the individual R, G and B master frames, definitely more pronounce with G and B filters.

[Jimbo_Aus (Jim)]

And here's the actual screenshot

[Sunfish (Ray)]

Hmm . Interesting.

Those images from PI are heavily stretched I think, and your image is quite stretched also which would amplify the problem . The rising sun look is pretty strange just the same .

I notice that this 1600 I am using is way more sensitive in Oiii than the previous one but I could not say why. It is cooled where the other was not. So much so I thought I had the filters mixed.

So perhaps variation exists in cameras for some bad QA reason or lower cooling makes it worse. I understand the micro lense problem is worse with fast and larger optics, although that could just be talk, and with reducers and correctors. You can always try less cooling or fix it in PS . I checked my subs and the effect you have is not really noticeable but I have only cooled to -10. Maybe that helps.

Originally Posted by Jimbo_Aus

Thanks Ray - this also happens with SHO imaging and in particular with my OIII filter (Astronomik 6nm 1.25"). I've attached a screenshot from PI of the individual R, G and B master frames, definitely more pronounce with G and B filters.

[Sunfish (Ray)]

Ps.
This explains why the effect is offset away from the centre although it does not help much

https://www.cloudynights.com/topic/6...plained/page-2

[Jimbo_Aus (Jim)]

Originally Posted by Sunfish

Ps.
This explains why the effect is offset away from the centre although it does not help much

https://www.cloudynights.com/topic/6...plained/page-2

Thanks again Ray, interesting read on the CN forum. I'm considering upgrading to a 2600mm but hesitant since I'd also need to upgrade all my filters.

[Jimbo_Aus (Jim)]

I managed to find an earlier version of this target I took with my 183mm pro and same filters and OTA. Definitely no microlensing effects I can see with the 183mm.