Filters + Gain + Binning + Exposure Time on IC1805

[JSeaman]

Hi all,

I'm working on my first picture (IC1805) on the ZWO ASI1600mm Pro using a 12" 300PDS (1,500mm, f/4.9). I completed the Ha previously and got some lovely data but my 3-4 hours of SII and OIII were really weak. I put this down to the full moon and had another go tonight in the brief clear spell. I was expecting a good amount of OIII and SII for this target based on examples like this: https://www.galactic-hunter.com/post/ic-1805-the-heart-nebula

I have been using unity gain (139) for the Ha and got some lovely data on 5 min/300s exposures. I am using a gain of 278 (I doubled it) and binning 2x2 and I still have very little OIII data. Has anyone got any thoughts or experience on this? I can go to 10 minute subs but I'm at a wildly different set up for OIII to the Ha (double gain, double binning and double exposure time) if I do this which feels a bit wrong

Some images below to show the issue:

 

1. Ha 300 second sub at unity gain (139)

 

2. OIII 300 second sub at unity gain

3. OIII sub at 278 gain

4. OIII with 2x2 binning and 278 gain

 

I'm just running a 10 minute exposure to see how that goes

James

 

[JSeaman]

Here's the 10 minute at 2x2 with the 278 gain, still not looking particularly great:

 

[JSeaman]

Any ideas guys? I tried a 20 minute sub and that didn't offer much either, has anyone shot OIII on a 1600?

[vlaiv]

What seems to be the problem?

OIII is faint and not very structured in the target you are imaging. You need to collect your data and stack it before you reveal the faint signal.

If you are imaging at 1500mm of focal length - you are working on quite high sampling rate and you should bin at least x2 if not x3 all your data.

Here is about an four hours worth of OIII data on Bubble nebula that I shot with ASI1600 at gain 139 and using 4 minute subs at 1624mm of focal length binned x2.

[JSeaman]

Hi Vlaiv,

Thank you for responding. From the pics I have been seeing (e.g. in the link above), there is a good amount of both OIII and SII but I have been pulling out vrey little indeed.

This is a 4 hour stack of O3:

Am I expecting too much or is this a good representation?

I was experimenting with binning last night and agree about 2x2 for future images

James

[vlaiv]

25 minutes ago, JSeaman said:

From the pics I have been seeing (e.g. in the link above), there is a good amount of both OIII and SII but I have been pulling out vrey little indeed

Well, it actually does not have that much OIII:

OIII in this image is that faint bluish background glow - you have exactly the same signal in your image above.

Btw, imaging in moon light is going to be damaging to your data regardless of the fact that you are using narrowband. Ha/SII usually feel the least impact by the moon - but that depends on filter bandwidth (3nm are better of than say 5nm or 7nm)

[JSeaman]

Thanks, I'll set to work on processing what I have then and see if I can get a decent image. 

Yes, part of my moonlight escapade was to evaluate how much of an effect it has on the data, the answer was a lot! 8 and 8.5 nm filters were being used

[JSeaman]

This is the best I have managed so far ...