ZWO 1600MM Cool - First Light + advice

[groberts]

If nothing else, I have learned from life – walk before you run.  I have spent the past three years trying to learn astrophotography with a DSLR + William Optics GT81 + AZEQ6 mount and late last year decided it was time to move on.  I was reluctant to go to a CCD mono camera as it clearly involves greater complexity and, perhaps most significantly, during the aforesaid period clear skies have been in very short supply – making long, guided exposures over protracted periods something close to mission impossible where I live.  However, with the very recent advent of the new CMOS cameras and rave reviews here and elsewhere, against my better judgement I took the plunge and have bought a ZWO 1600MM Cool  + matching x8 EFW.

Wow! As expected, it’s a whole new world compared to DSLR and as well as continuing cloud week-after-week, I have been battling with numerous set-up and processing issues. Still, rule number one with this hobby is patience and perseverance.  And so this week I managed my first reasonable image of the Rosette with the camera, which I am quite pleased with.  Notwithstanding, I’m wondering how to improve from here and specifically what I need to do differently?

·        The image is guided, 15x180sec Ha-subs + darks and bias, gain 300, offset 10 + minor stretching in PS.  The corners – particularly the bottom right – looks like vignetting?  I haven’t managed to achieve any decent flats yet (another story) but I assume these would help eliminate this effect?  However, I wonder why it’s there at all as I’m using the ZWO EFW with 31m filters and the camera + focal reducer FL of 382 (f4.72), which should not result in vignetting. Any thoughts?

·        Clearly experimentation is still ongoing with this new technology but what is the ‘best’ exposure, gain and offset for this type of feature + is there a rule-of-thumb for other objects e.g. Ha-nebulosity, galaxies etc?

·        Finally, my nemesis – focus.  I’m using APT for capture now, though already have SGP and intend to move over once I’ve got the basics working with the camera.  It’s immediately clear that focus is more critical with this type of camera compared to the DSLR – I’m using a Bahtinov + the Bahtinov Aid in APT – which seems OK but I’d like to do better. Any ideas?

I understand there’s a lot here but would appreciate any guidance, tips or advice.

Many thanks, Graham 

      

 

[JemC]

I'm sorry i can not give you any advice/tips but i think it is a cracking image 

james

[Gina]

That's a great image - well done   I use shorter exposures of around 60s and higher gain to match, up to the maximum of 600 for the faintest DSOs plus a large number of subs - in the hundreds.  This method can capture during gaps in the clouds and make use of nights otherwise unusable.  It does generate a lot of data though.

[Filroden]

Flats should resolve any vingnetting but I can't help you with what to expect with your gear combination.

The Rosette is relatively bright and I got decent Ha signal at 60s at unity gain. This was when I was exposure limited by my mount. I'd now push this to 120 or even 240s whilst dropping gain to extend dynamic range.

As for focus, one of my best investments was a Lakeside focuser controlled through SGPro. I get pin point focus all night (it recalibrates every degree change in temperature and every filter change). No matter how much time I'd take, I could never get the same quality of focus using a mask, even with software assistance.

[Mick J]

As a quick tip, couple of diy focus (stepper/arduino) in the DIY Astronomer threads.  If you are handy can be super cheap.