Rosette Nebula SHO

[groberts]

You can blame me: I purchased a set of Chroma filters last October and have been unable to image ever since due to the weather! At last in late February / early March I managed a few hours albeit at full moon, so for my 'first light' experience of these filters went narrowband.  Whilst I'm happy with the attached Rosette image - certainly the 3nm SHO filters have improved the stars when compared with my previous ZWO filters - there were a few things:

• For the first time I went to 10 minute exposures as, I presume, the 3nm filters seemed to 'need' more light?
• I also did a quicky and dirty LRGB of M42 (not yet processed) to try out the other filters and was surprised to find the Luminance very overexposed at 180 seconds compared with the ZWO luminance filter using the same exposure & Unity settings.

I would be interested to hear from others who use Chroma filters and their experience and thoughts on how to get the best from them e.g. I've always used the ZWO ASI1600MM Cool camera + ZWO filters at unity with good results but maybe the Chroma would benefit from higher gain etc.?

Graham

 

            

[Adreneline]

Very nice image Graham - really like the colours and the sense of depth you've achieved.

Sorry I can't offer any insight into the filter questions you pose.

Adrian

[MartinB]

That is a beautiful image Graham. 

I can't comment on the luminence, does the Chroma block IR?  Re gain settings, certainly getting over the read noise is the challenge with ultra narrow band pass filters however the low read noise of CMOS cameras is a game changer in this regard.  If you look at the gain/read noise graph you will see that there is a diminishing return in lowering of read noise with increase gain and a slowly increasing fall off in dynamic range so there is an increasingly severe penalty associated with increasing gain.  I use a gain of 120 with my ASI1600MM pro (I've never attached any significance to unity gain other than it being a statistical quirk but 139 happens to be a reasonable value!).  If your sky values are more than 500ADU I think you will be over the read noise.  

[groberts]

Thanks all much appreciated.

My problem with much longer exposures is (a) light pollution (b) aeroplanes (when they're flying) and (c) polar alignment and its impact on set-up + guiding etc. as I cannot see Polaris - my house is in the way!  

Can't do anything about light pollution except move = watch this space, make the most of the current lack of flights (I live between Gatwick - Heathrow airports + Redhill aerodrome down the road - of course I didn't do astronomy when I moved here!) Using PHD2 polar align routine + with the new multi-star guiding choice my guiding error is at last now looking very good.  The 10-minute exposures this time worked out well + it cuts down data use, though still unsure about how to use the LRGB filters i.e. exposure times .  

I think more experimenting will help but overall the new filters are good. 

Graham           

  

Edited March 12, 2021 by groberts

[AndysAstroPix]

Hi Graham, nice image with bold colours.👍

I have Chroma filters and also image under LP bortle 6 suburban skies in Melbourne, Australia 🇦🇺 (pop. 5 million)

As such the Chromas perform very well under these conditions - on par with Astrodons (I've used both) . I generally use 15min subs for 5nm Ha & S2, 3nm O3 filters with my f7.7 tak QSI 6162 combo. 

I rarely get under dark skies so have little use for my LUM filter, but with my sky conditions, lots of 120 sec subs produce nice R,G & B stars.

These settings may not translate directly to your CMOS sensor though, so keep up the experimenting! 😉

Cheers

Andy

Edited March 13, 2021 by AndysAstroPix