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Now that's what i call a dark frame


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Hello girls and guys,
just out of curiosity i tried to get a grip on the noise of my new used QHY8. I'm sharing a 30 sec sub with a low gain setting that would somehow translate into ISO 100-400 with a Canon (roughly):dark30secs.png

The frame is completely pitch black, even with heavy stretching! With the only notable exception being 4 hot pixels (all of them green). I stretched it 3 times in Gimp with no visible noise.
I guess as long as the Gain is kept so low, i even might ignore the darks completely (?). I will try my first DSO's ASAWA(as soon as weather allows), process them with and without darks, and will share the result here.

Dark skies!

 

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Hello guys and girls,

just in case somebody stumbles upon this thread, this would be the steps i should have done before taking darks:

Quote from the doc (the procedure should be the same for QHY9,QHY9L, and possibly other units as well):

Setting the GAIN and OFFSET

Unlike many other manufacturers, QHYCCD leaves the the internal settings of the camera ADC GAIN and OFFSET settings so that you can get the absolute best performance out of your CCD.

GAIN is the pre-ADC programmable gain amplifier gain setting, the range is from 0 to 63.

OFFSET is the ADC voltage offset setting.

The correct setting of OFFSET and GAIN can change the CCD camera system gain, which match CCD output signal range and scope of the quantitative ADC to get the best dynamic range.

Usual Calibration Method:
1. Set the Gain=0
2. Set the exposure time to 0 and cover the lens-this is a BIAS frame .
3. Watch the local average of the captured images (can use the Noise Analyze function of EZCAP)
4. The ideal average value is around 500 to 1000. If the value is higher, then you should reduce the OFFSET. If the value is lower then you should increase the OFFSET.
5. Repeat steps 2-4 to obtain the ideal OFFSET value.

6. Open the lens cover and increase the exposure time. Use a uniform light source, such as light boxes or an LCD screen, and take a saturated exposure of the image.

7. Watch the local average value of the captured images if the value is is less than 60,000, you need to increase the value of GAIN, if the value is 65535, then reduce the GAIN .

8.Repeat steps 6-7 to obtain the appropriate GAIN value.
9.Under the GAIN, repeat steps 2-4, and obtain more accurate OFFSET

 

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