QHY8L - Good Idea/Bad Idea?

[russellhq]

When the temp reads -20 on te bottom bar in EZCAP, does this mean the sensor is at -20 degrees, or is the sensor at 20 degrees below the ambient temperature?

Do most people just select auto and let the software work out how much power to devote to cooling to maintain the chosen temperature?

Do qhy8l users use darks?

James

The temperature shown is the actual sensor temperature and not the delta.

I used auto and selected the temperature I wanted, which was normally - 20C.

Yes, you have to use darks with the QHY8L because of amp glow during the reading process. I think this is documented in the manual.

[jambouk]

Thanks

James

[nightcasper]

I used 4 seconds bias to get around the amp glow and never used darks but it's best to do some tests of your own.

Dave

[Thalestris24]

Hi

There have been various incarnations of the driver, one of which showed bad amp glow. However, the most recent only shows it with long exposures - >=1200s, from memory. Shorter exposures don't seem to need darks.

Louise

[jambouk]

What is the best way to see potential amp glow, as the darks i've made are pretty dark

James

[jambouk]

"The issue is, when QHY8L use the long expose time
mode, after the 1st frame exposes over and it is
reading out, the 2nd frame is exposing. When the 1st
frame is reading out, the AMP light will show, but the
2nd frame is exposing all the same. So the AMP light
will be photoed on the 2nd frame. The AMP light’s
time is about 1.45s(high speed download) , or
3.47s(low speed download) . The AMP light is yellow.
It can be calibrated by taking dark frames.
When using 2*2 or 4*4 mode, QHY8L use the
progressive, so there is no AMP light problem occur."

From:

http://qhyccd.com/file/repository/PDF/QHY8L%20user%20manual.pdf

James

[jambouk]

This is a very heavily stretched 300s dark shot on the QHY8L at -20. I think Fits liberator flipped the image hence the presumed amp glow is bottom left rather than top left.

I'll have to see how the camera performs in real life to know if I'll need darks or not. I'm aiming for 600s subs, so I'll repeat the dark at 600s and look again at the amp glow.

James

[jambouk]

Four darks, 300, 600, 900 and 1200s and stretched in a very similar fashion in PS (CS2).

James

QHY8L darks.pdf

[Thalestris24]

Four darks, 300, 600, 900 and 1200s and stretched in a very similar fashion in PS (CS2).

James

Hi James

Hmm... is it meaningful to stretch darks to that extent? If I stretched any of my lights so much they would be pure white! (I do suffer from very bad lp...)

Louise

[jambouk]

I only stretched them so much to bring out any amp glow, and to see if it differed for different length subs. I've no idea if subtracting darks will be beneficial when i have some data, as this amp glow is very subtle and as you say only evident when stretched to the absolute max. I'll have to wait for some data to see.

James

[Zakalwe]

The amp glow is fixed in these cameras as the amplifier is active for a fixed period during read-out. It will not become brighter with long exposures.

Darks will take care of it easily.

See this topic:

http://qhyccd.com/ccdbbs/index.php?topic=4328.0

[russellhq]

Since the amp is only on during download for a fixed period, then exposure length shouldn't matter. I think you have shown this in your attachment. Nightcasper's use of 4s bias frames is an interesting way to go and might be all you need to do.

[jambouk]

I only conducted the test to see if the suggestion above that amp glow more problematic with longer exposures, which it does appear to be and that would make sense if the period the amplified is on is fixed whatever the exposure length.

I'll look at a bog standard bias, and a 4second dark and see if there is any difference.

[jambouk]

As shown, the amp glow is evident on the 4s dark, but not on the bias. I think that concludes how i'll be addressing the amp glow when I finally have some data.

Thanks

James

bias.pdf

[Zakalwe]

As shown, the amp glow is evident on the 4s dark, but not on the bias. I think that concludes how i'll be addressing the amp glow when I finally have some data.

Thanks

James

it won't appear on the bias as the bias exposure is so short.

[jambouk]

Is the sensor "read" when taking a bias frame? If it is, why is the fixed period amp glow evident?

James

[Baffa]

I also use 4-5 second bias. Also, the amp glow should be constant, if it varies with exposure it's because of the bad ascom driver. I haven't tried the latest driver so I don't know if it's fixed but their own software, Ezcap, works ok.