Qhy8L bias

[Earl]

As the QHY forum is down, do any of the QHY8L users have a recommended Bias exposure length.

There is a thread on the official forums regarding it but i cant remember the details now.

[cgarry]

Are these bias frames to calibrate your flats? If so, how long are your flat subs?

Cheers,

Chris

[Earl]

Im not using them for Flat, as im currently struggling to get my Flats right :|

[martin_h]

I always thought that Bias should be as short as possible...my QHY9 I use 0.001 sec

[cgarry]

If the exposure time is less than 3.47 seconds then the QHY8L actually does 2 exposures so that each interlaced frame is exposed for the same length of time. If the exposure is greater that 3.47 seconds then a single exposure is used and the second frame gets a longer exposure as it is still being exposed while the first frame is being read out.

From reading the QHY forum, my understanding is short bias frames using the double read out mode will not correctly match longer subs using the single readout mode. To get around this, the bias frames should be a bit longer (say 4 seconds) to be sure both the bias frames and the subs being calibrated are using the same readout mode.

If you are calibrating flats less than 3.47 seconds long then very shorts bias frames are the way to go as they will both be using the same readout mode.

Cheers,

Chris

[Earl]

Cheers Chris

I did look at that thread but it didnt "Penny drop"

So in the case of the QHY8L a 4 Second Bias is needed for 300s subs.

This does explain the amp glow issue i am getting, ill need to redo my bias collection.

Ta

[Earl]

Due to this issue, when making a flat master, i presume I also need to use a fresh set of Bias and Flat Darks ?

[Earl]

The reason I ask is this on the pixinsight tutorials

"In the Master Dark section, be sure to enable the Optimize checkbox. This will rescale the master-bias-subtracted master dark to fit the thermal noise of each flat frame. Don't worry if your master dark has 1000 seconds of exposure and your flat frame is only 10 seconds: IC will multiply the thermal noise of the master dark by 0.01."