QHY8 Camera...opinions needed

[narrowbandpaul]

Hi Guys...

i read the QHY8 has double TEC cooling, what drop in temperature does this correspond to, and is the temperature controllable?

I read it is a progressive scan, rather than the orion starhoots version with interlaced scan?...what is the benefit in progressive., particularly in relation to read noise...etc

I read that the gain on the preamp (uV/e-) can be controlled by the user...this has the effect of varying the sensitivity of the camera...increase gain, means larger uV/e-, meaning higher DN per electron...which is basically higher sensitivity.

I take this to mean...higher DN per electron, higher sensitivity (more DN for given signal), but 65535 is reached BEFORE full well...so your dynamic range is reduced

low DN per electron means full well is reached before 65535 is reached..basically it looks like lower sensitivity, but smoother image

Can someone with experience of this camera help answer these questions, or someone with a technical knowledge

Thanks guys

Best Wishes

Paul

[iancandler]

Give Bern a ring at modern astronomy Paul, he will be able to answer all your questions.

[Ben Ritchie]

The only bit that I can answer is that the temperature is not strictly controllable, it's a delta from ambient (although I believe there is a QHY8pro coming out where it is?). You can apparently vary the input voltage to the peltier in such a way that it approximates setpoint cooling, but that's not possible with the standard power supply.

... I think ...

[MartinB]

Yes Paul, the gain and the offset are user adjustable. The offset can be adjusted using a bias to ensure that the darkest level is more than zero. The gain can be upped to minimize quantization error but, as you say, shouldn't be at the expense of loss of dynamic range and clipped white points. Best way to set is to image on a bright day time object and to make sure the historgram has fallen off before clipping. Because the chip is non linear it's best not to make this too close to the levels limit.

As Ben says, cooling on the current model isn't user controllable. The dark current is very low though and dithering should take care of dark current effects

It is progressive scan. I have a QHY8 FFT of a read noise frame here but it doesn't look right http://stargazerslounge.com/index.php/topic,33955.0.html.

[narrowbandpaul]

Cheers martin...

didnt know that offset values are adjustable, I cant think that will have much effect, but the variable gain certainly will.

How non linear is the chip?...not too much I hope

the non set point isnt too much of an issue...as long as the dark current is very low (should be for Sony)...if the voltage to the peltier is controllable, then this is fine...

the read noise frame FFT worries me...

Is there a QHY8pro coming???

Thanks again Martin, and ben

Paul

[SteveL]

QHY8Pro is a sealed unit, so no more "horror stories" of frosted CCDs (cured easily by storing the original QHY8 in an airtight box with silica until you need to use it).

Image below is final version but unpainted. The retail version will be matt black.

[MartinB]

I might redo that FFT Paul.

TBH I don't think the adjustable gain is that important. Although in one sense raising the gain increases sensitivity it doesn't actually improve s/n ratio. It does improve the accuracy of the level allocation of non integer values. The gain is normally set to 50% but some people boost this to 60% on dim targets. My guess is that leads to quite a loss of star colour, I don't have any plans to do that.

It is an ABG chip with a high (>60%) QE rating extended into Ha. I thought there was a curve for the chip on the SX web site but there isn't.

As Steve says the main benefit of the pro will be better sealing of the chip reducing the icing and condensaion problems of the current model.

[narrowbandpaul]

thanks...

yes, i have been thinking quite a lot about variable gain...and the lies that it spreads...

The only meaningful number is the number of electrons collected...not DN...I have been thinking this for the ISO meaning on a DSLR...

When will the QHYpro 8 be released

Thanks martin and steve L

[anthony]

No date for the pro yet.

Anthony

[narrowbandpaul]

cheers anthony

[iancandler]

http://www.qhyccd.com/ccdbbs/

[narrowbandpaul]

great link Ian cheers...

QHY8pro should be out soon...

is Bern at Modern Astronomy the best source (cheapest) or should I also try elsewhere?

Cheers

Paul

[FLO]

Bern at Modern Astronomy is definitely the BEST source for QHY here in the UK