DSS / Ha Filter issue

[mikeonnet]

Hi all,

Assistance needed please. Having recently purchased a mono camera (Zwo 290mm cooled), with LRGB & Ha filters, I tried it out the other day on the Cocoon nebula. The LRGB filters seem fine, however, the results from the Ha filter are dismal.

I have attached 2x images (both from the same subs) which were 300 second, total (2hr 10min) exposures in Ha. The 1st image was using DSS "Average" stacking mode which is blotcy and the 2nd "Auto Adaptive" method that DSS suggests to stack with, I have no idea what's going on. You can see it appears I have amp glow? in the corners but I cannot see this 'Glow' on the RGB subs, although I used 180 second, 2x2 binning for the RGB subs.

Any idea's / suggestions please?

 

[Thalestris24]

3 hours ago, mikeonnet said:

Hi all,

Assistance needed please. Having recently purchased a mono camera (Zwo 290mm cooled), with LRGB & Ha filters, I tried it out the other day on the Cocoon nebula. The LRGB filters seem fine, however, the results from the Ha filter are dismal.

I have attached 2x images (both from the same subs) which were 300 second, total (2hr 10min) exposures in Ha. The 1st image was using DSS "Average" stacking mode which is blotcy and the 2nd "Auto Adaptive" method that DSS suggests to stack with, I have no idea what's going on. You can see it appears I have amp glow? in the corners but I cannot see this 'Glow' on the RGB subs, although I used 180 second, 2x2 binning for the RGB subs.

Any idea's / suggestions please?

 

Hi

I'm afraid I'm not familiar with the camera and don't know how to set it up but most people only seem to use it as a guide cam or planetary cam (it has a high qe). I'm not sure how well it performs with long exposures/dso targets. I wonder what gain settings you used? What about calibration frames? What were individual Ha subs like? Have you tried Kappa Sigma stacking - that usually gives good results if you have 15 or more subs.

Louise

[mikeonnet]

Thanks Louise. Yes, regarding the camera I know it has a small sensor and narrow FOV but for small DSO's I thought it would be suitable to use.

Regarding gain, I had this set to "Unity Gain". I cant remeber the exact gain level (110 rings a bell) without connecting the camera again.

The subs all came out very dark with just a handful of stars showing and no nebulosity showing until DSS has stacked them all. Would this be normal for Ha? - I just assumed as it was Ha, the subs will appear virtually dark until streched. I have a lot to learn with mono imaging.... These were 300 seconds each sub.

Lastly, the preview above do not have any calibration files attached to be honest. I did take Flats but the output file was the same. I guess it would help with vignetting when streched but I didnt take Darks as I had the sensor set to minus 10c. but I will try next time with Darks, Flats etc.

It just seems I'm getting far better results with my humble Canon DSLR (not modded) espcially as I took over 2 hours of exposure time with just the Ha filter alone - although the Moon was close but again, I though Ha would block the light from the moon.

I shall keep trying and experimenting but I do not want to upgrade to an ASI1600mm for instance and have the same issues, just a bigger image and I cannot afford one anyway!! ?

Mike

[Thalestris24]

Hi Mike

You probably really should take calibration frames. I can't really advise on the correct settings for your camera - maybe someone else on here can help. I think @Anthonyexmouth has used a 290. You probably need to get the gain right so need take some test subs at different gains and/or see what anyone else might have used for DSOs. The asi cmos cameras only capture in 12 bit whereas DSLRs generally capture 14-bit raw files. I think that's maybe why your subs look dark. Doing Kappa Sigma stacking should help so long as you have >15 subs to stack. Don't use the remove hot pixel option in DSS - it can make holes in your stars! Calibrating with darks should remove any hot pixels. What temperature were you running at? You may need to be set below -15 deg. Maybe post another question re best settings for your camera and recommended calibration frames to take.

Louise

[geordie85]

With these new cmos cameras calibration frames are an absolute must. Especially dark frames as these will remove the amp glow. The longer your subs, the more amp glow you'll see. That's why it's a lot more present in your longer Ha subs. 

With my cmos camera (qhy183c) I always use flats, darkflats and darks for calibration and my images are free of amp glow and defects/ dust bunnies. 

[mikeonnet]

Thank you for your replies. I shall try various gain settings along with the darks etc and shall see what happens for the next clear skies. As the saying goes, it seems like im trying to run before I can walk with mono imaging. Thanks again.

[wxsatuser]

15 hours ago, mikeonnet said:

- although the Moon was close but again, I though Ha would block the light from the moon.

Although it can negate the Moon to a certain extent it will not stop it washing the image.

If the Moon is about I try to get it away as far as possible.

I did the Flying Bat and the Spaghetti with the Moon about and they were both washed out a bit, two I need to do again.

[Thalestris24]

21 minutes ago, wxsatuser said:

Although it can negate the Moon to a certain extent it will not stop it washing the image.

If the Moon is about I try to get it away as far as possible.

I did the Flying Bat and the Spaghetti with the Moon about and they were both washed out a bit, two I need to do again.

Indeed! Even a 3.5nm Ha won't keep nearby bright moonlight out! It's Satan's Lightbulb, ha ha. The Moon's spectrum isn't that different from the sun - not surprising since moonlight is reflected sunlight. Moonlight is much less intense, of course.

 

I've taken a few images of the Moon in Ha before now  

Louise