My Ha sub-frames are totally clipped in the black point, what could cause this?

Sequence Generator
1

Hi everyone,

I’m using a QHY9M and I took multiple sub-frames of NGC7000 from Portland Downtown using a Baader 2" Ha filter 7nm. For whatever reason, the subs can’t be stretched. The black point is totally clipped. Could the offset or gain setting cause this issue?

Here is the dropbox folder with all the information: subs, master dark, master flat, master bias and bad pixel map files.

https://www.dropbox.com/sh/0zwp2cb252sbyj0/AABidnU2-plcidpb_C2LSnB2a?dl=0

And here is a list of screenshots on how I have the QHY9M configured in SGP

[5 new items added to shared album] Astronomy

Does anyone have any thoughts?

Best,

Miquel

2

You have the gain set at 0% and the offset at 60. Try upping the gain, my QHY9 needs a gain of 25% and an offset of 100

3

Hi Martin,

Thanks for the answer. I will change the settings and try again.

Best,

Miquel

4

Hi Martin,

I read about how to determine offset and gain. I found my offset value at 115 using the bias method. I’m now trying to determine GAIN by pointing the camera to a daylight object while taking a 0.01 second frame of a daylight object. However, I have a question. My filters are green, red and blue, plus Ha and OIII. I usually use my green as luminous equivalent. Am I supposed to use the green filter to determine gain? I assume I don’t have to use the Ha filter, right?

Thank you,

Miquel

5

Yes use the green.

6

Thanks Martin!