ASI1600 cooled - strange bias subs

alcolmoon

just taken delivery of a replacement ASI1600 and began by taking bias subs for the library. I took and stacked 300 subs using the standard Pixinsight integration tool. The subs were Gain150 offset 21 and the fastest camera speed of .000032, I also did some with an exposure of .001.

I have attached a copy of the master Bias produced from the 300 subs. AS you can see this is splattered with black pixels and very little in the way of banding. Any ideas if there is something wrong with the master bias or is this normal

I have also attached the superbias although I understand that the current wisdom is not to use this as the banding of these types of chip are not all in the same direction (whatever that means!)

Sam comments on the black pixels would be appreciated

Thanks

alcolmoon

By way of an update. I have produced a Master Bias for various Gain/offsets (75/15, 139/21, 200/50 and 300/60) all have the black pixels. When I align the master bias' the black pixels are in exactly the same places on the images.

I have used the master bias' to calibrate flat frames and the black pixels do not seem to show up on the calibrated flats.

Sam: have you got an explanation for the black pixels??

Thanks

Alec

Sam@ZWO

sorry for later reply, I will try to repeat and reply you tomorrow

alcolmoon

OK Sam, look forward to hearing from you. Regards Alec

Sam@ZWO

seems this is because the offset is not larger enough

you can add the offset value

alcolmoon

Hi Sam

Thanks for the reply. See my earlier post, I took and made master bias with various gain and offsets: Gain/offsets (75/15, 139/21, 200/50 and 300/60) all have the black pixels.

And all have the dark pixels, I don't think it is that unless I am missing something?? Any other thoughts?

Alec

Sam@ZWO

I did this test myself

the offset need to be higher

for example: 139/60

our suggested offset value seems too small

alcolmoon

Hi Sam

I was working on the basis that the gain and offset settings for producing bias frames and therefore the master bias had to be the same at the settings used for the darks and light images?

Is this incorrect?

Alec

alcolmoon

Hi Sam

I have run the camera again with gain at 139 and offset 60 as per your test. The master bias I produced still has black pixels on it, albeit not so many. I have the statistics from Pixinsight on the various master frames I have taken if these would be any use to you. They mean little to me!

Regards

Alec

Sam@ZWO

alcolmoon wrote:
Hi Sam

I have run the camera again with gain at 139 and offset 60 as per your test. The master bias I produced still has black pixels on it, albeit not so many. I have the statistics from Pixinsight on the various master frames I have taken if these would be any use to you. They mean little to me!

Regards

Alec

Hi Alec

dead pixels just like hot pixels

they all exist on a sensor

so it should be normal the sensor has dead pixels and very few of them

the camera in my hand have such black pixels too

alcolmoon

Hi Sam

I assume that if they were dead pixels they would appear when I subtract them from the flats? They don't show up, neither are they obvious on the individual bias frames. I have looked again at the histogram of the master bias and the individual "black" pixels have a level of around 230 ADU when measured on the master bias produced with a setting of "unity"

All a bit of a mystery

Alec

Sam@ZWO

alcolmoon wrote:
Hi Sam

I assume that if they were dead pixels they would appear when I subtract them from the flats? They don't show up, neither are they obvious on the individual bias frames. I have looked again at the histogram of the master bias and the individual "black" pixels have a level of around 230 ADU when measured on the master bias produced with a setting of "unity"

All a bit of a mystery

Alec

you are correct that they maybe not dead pixels because you cannot see them in flat

but my knowledge cannot explain

alcolmoon

OK Sam. If this occurs elsewhere and you find an answer please let me know. I will continue with the camera and keep a close eye on these particular pixels and get back to you if I notice they are affecting my final images. In the meantime if anyone else produces these dark pixels it would be useful to know.

Regards

Alec

On a completely separate topic, what price an 8 position filter wheel direct from China?

Sam@ZWO

alcolmoon wrote:
OK Sam. If this occurs elsewhere and you find an answer please let me know. I will continue with the camera and keep a close eye on these particular pixels and get back to you if I notice they are affecting my final images. In the meantime if anyone else produces these dark pixels it would be useful to know.

Regards

Alec

On a completely separate topic, what price an 8 position filter wheel direct from China?

no problem, here is the price of EFW, I think shipping would be $20

https://astronomy-imaging-camera.com/products/filterfilter-wheel/zwo-efw-8-x-1-25%e2%80%b3or-7-x-36mm/

alcolmoon

Thanks Sam