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I agree

PI integration of noisy narrowband subs

23 Sep, 2019 13:37
I chose NGC 896 as the subject of my first attempt at narrow band imaging and captured about 100 Ha subs over the weekend. (example with aquisition details) I had to adjust the active curve tool in Backyard EOS to see the nebula as I was capturing and did not notice the heavy noise until I came to process. I have not been able to get the images to stack, presumably because the Batch Preprocessing tool cannot tell stars from noise. You can see the nebula is there but wondering if the subs are too noisy to even bother trying to extract it. Thanks in advance.
24 Sep, 2019 16:15
A couple comments … narrowband generally has a better signal/noise ratio than broadband filters … but the signal may still be low. Next time out, try 5 minute exposures and work up from there. I typically do 10-minute (18-30 lights per channel if the weather is playing along) and a lot of folks go longer. But more time will give you more signal.

Second, if BPP isn’t working, you can always fall back on manual preprocessing: image calibration, star alignment and image integration. That may give you more control over and influence on the process, especially star alignment. I suspect your data is usable but you may need to gently play with the star detection parameters to help with alignment.

Hope that helps! — Joel.
24 Sep, 2019 16:37
Thank you for the response Joel. You raise some great points. I'm not in a rush to process so I will absolutely take your advice and recapture the subs with a longer exposure time. My mount is not high quality and I have not had great success getting round stars when I exceed 3 minutes. Typically guiding within 4 arc seconds is a good night but I'll see how far I can push the exposures.

As a fall back, I will try manually registering the subs. I have avoided this in the past as BPP can usually be persuaded to automate the process accurately by playing with noise reduction. This time though, I have so far failed. I will try again with longer subs and hopefully that does the trick.

Thanks again.

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