Narrowband First Light

[Jbro1985]

Hi all!

I'm about to embark on my first narrowband imaging session tonight.  

If you're happy to share, I'd be interested to know the one thing you wish you had been told before you started with narrowband, what challenge it caused you and how you overcame that challenge?

For some context, I've been imaging LRGB to now so have some general experience.

Tonight, I'll be using an ed80 pro refractor with 0.85 reducer, moonlite focuser and motor, OAG, asi185mc guidecam, efw, asi1600mm-c on an azeq6gt.  Filters are baader ha 7nm, OIII 8.5nm and Si 8nm, all 1.25".

I'll be using sharpcap to polar align and SGP for acquisition.  Current expected target is Elephant's Trunk.

Thanks all!

[Jonk]

I would get your focus spot on and then don't be afraid to push your sub length to 30 mins if your mount alignment and guiding is good enough.

Good luck and keep trying if it doesn't go well the 1st time!

[Laurin Dave]

Use long enough but not too long exposures and use the right gain..  I use Unity Gain and exposures of 5 or 10 minutes with my ASI600 for narrowband, seems to work well.. the longer exposures give me smoother images for the same total integration time, although I don’t know why this is..  quite a few posts on here about what settings to use, 200 gain 50 offset used by others.. 

Dave

 

 

[ollypenrice]

Yes, I like 30 min NB subs with some CCD cameras but CMOS won't thrive on them. Watch your focus like a hawk and save Ha for the moon if you're running out of time. OIII is much less moon proof.

Olly

[RichLD]

I have a QHY163m which is similar to your camera and find I can push exposures to 600s at G100 OS 70 (not sure what the ASI equivalent is) - more than this and the amp glow becomes too much for comfort. As others have said, watch your focus! I use a Bahtinov at Bin 1:1 and expose for 20s or so to get strong spikes. Filter used is a Baader 7nm.

Even though the general opinion seems to favour high numbers of high gain, short exposures with CMOS cameras, I still prefer the results I get using longer, lower gain ones. I feel the results are smoother and deeper, but that's probably just me ?

My standard HA sub settings for CMOS are 600s, -15C, G100, OS70 at around f/3. When using my QHY9m (CCD, KAF8300) I'll go for 1200-1500s subs at -20C.

HTH

Rich

[Hallingskies]

Focus.  Focus.  Focus.  And then check that focus, especially if you are working at f6 or less.  I’ve learned that “good enough” usually isn’t.  And it’s certainly worth rechecking during an imaging session - autumn can give you a 15 degree difference in ambient temperature over a six-hour session and it can be frustrating to sift through a pile of subs and see the star sizes gradually getting bigger and your fine nebulosity vanishing.

If your budget and set-up lends itself to a motorised/automated focusser then go for it.  

[Jbro1985]

Thanks all.  Focus it is! 

I've changed target to Heart Nebula, and looking at the "Valve" in particular.  No reason other than my house being in the way of Elephant's Trunk.  Got mixed up on my planning!

Anyway, I'm going with 18 x 300s exposures with on each filter for the sequence, with autofocus every 10 frames and on filter change and dither every 6 frames.  The first sub just came through:  https://jbconsult-my.sharepoint.com/:u:/g/personal/jbro1985_jbconsult_onmicrosoft_com/ETn2zxEcdGRNnDx7gyPomBMBvW_ztxonQ-NSGJoO2eMYAw?e=O9jh6I

Fingers crossed.  I won't get time to process until the weekend.

[Laurin Dave]

I'd check your guiding, there's some star elongation on that one

Dave

[Jbro1985]

Thanks Dave.  Elongating towards the top right, I think.  Seems to be getting a bit better frame by frame.

I've just got the mount back from repair (motherboard blew) / tuning and it's still running in with the new greasing etc. so guiding is a little off.  Phd2 also needs a recalibration for the same reason... backlash has been dialed out etc.  though it's giving me an RMS of 0.7 and gradually coming down.

I'm going to live with it for tonight and look to get the guiding all set up perfectly at the weekend, if there's a clear sky. 

[Laurin Dave]

Jason

I've got an AZEQ6.... maybe the Dec is bouncing... mine does unless balance is quite camera heavy.  Or maybe there's a bit of flex in the system, my ZWO OAG top wobbles on the stem even with the grub and locking screws really tight.. I think they should be at right angles (like the ones securing the stem top the OAG body)rather than facing each other across the stem. I wedged a bit of paper between the OAG stem and the top and it no longer does..  

 

Dave

[Jbro1985]

I'll definitely check that our.  I get a tiny bit of wobble, OAG is facing upwards with the camera on top when scope is parked.  Does this look familiar?

[Laurin Dave]

Yep, my Dec is always worse than RA... and I sometimes get a PHD graph like that.  If I do I recalibrate, and put a bit more weight camera ended rising side.  I also use 1" guide camera exposures...  chases the seeing but stops the mount going AWOL.

Dave

[Jbro1985]

Well, SGP did it's thing.  Ended up with 18 ha, 18 OIII and 4 SII subs.  Meridian flip failed whilst I was sleeping. 

I expected some buggeration because I've just set everything up from scratch on a remote PC so I'm not too frustrated with that.  I know the issue so can hopefully test and confirm.

I'll post the final image over the weekend.  Tempted not to integrate the SII into the final image due to the lack of data but was good skies last night so I will see how it all looks in SHO before rowing back to HO.

Thanks for your help last night Dave!

[Zakalwe]

You mightened need such long exposures with the ASI1600. Ten minutes will get a lot of data and more subs can help with smoothing out the noise compared to fewer longer subs.

[Jbro1985]

Thanks Zakalwe. 

I acquired 5 minute / 300s subs.  Did you mean 10 mins or 5 mins when you said about shortening?  I'm keen to find the optimal exposure.

[Jbro1985]

Here's my first very quick processing.  Darks used but I haven't applied flats etc and I only spent about an hour on it.  Lots more work to be done and the data isn't amazing.  Good practice though.  I've blown out the core a little on this one.

[geordie85]

A very  nice result with plenty of detail. You should be happy with that.