Hello everyone, I have recently acquired a second-hand SBIG ST8XE ABG and I was surprised that exposing to BIN1 the accounts never exceed 40,000 adus, this is strange for me, this has never happened to my previous CCDs. I also find that when taking a 600" shot in BIN1 focal 1600mm with Astrodon V filter, it has picked up so little signal (see attached image of M60) I wonder if this is normal and if this affects the dynamic range of the camera. Thanks in advance rgds, Luis
Full well on the KAF-1602 is 50,000 nominal. If it's an ST-8XE, it's probably 20 years old, so your expectations should be appropriate. What's the serial number? You can contact Bill (at) sbig (dot) com about adjusting the camera. It might be possible, but I doubt it. It's likely beyond its serviceable life. The electrolytic capacitors in the power supply and the circuit boards likely are far out of tolerance due to age. Try a different filter and a bigger/faster scope on M60.
Thank you for your comments, the s/n is 810005789XEA. I emailed Bill and he told me to start this post. I understand that this "blindness" is due to the fact that it is at the end of its useful life? Excuse my ignorance, so these cameras never reach 65535 accounts? I attach an image, same focal length, 600", without filters.
Ok, I looked up some manufacturing history on that camera. The good news is that it is performing very close to the original specification, if you are seeing saturation at around 40K ADU. The KAF-1602/1602E in your camera was a sensor designed in the late 1990's, and it does not have microlenses and it's QE curve in the V band is about 55%. So half the photons are detected. That doesn't account for the transmission of the filter, which will mean less light gets through. Later versions like the STF-402 used the newer KAF-1603E with microlenses; That CCD chip's peak QE was 82% vs your chip's peak QE of about 61%. Exposures on your camera would take about 25% longer than the more modern version. That camera was dated 2007 during manufacturing tests, so it is 15 years old. The KAF-1602 sensor has a full well depth ranging from 85,000 - 120,000 electrons (e-) per pixel. Each particular sensor is different - remember these are analog devices - and are calibrated at factory. There is an offset of about 1000, and then that range from nominal black to full well is mapped to the Analog to digital converter's 65535 values. Your camera's egain was factory set at about 2.58, so that it can map those theoretical 120,000 electrons to the 64K values. So it should saturate somewhere around 40-46K ADU, not accounting for that offset. It appears to be behaving correctly if you're seeing 40K ADU at saturation. Some things I've noticed: N.I.N.A. acquired your sample image, and it is incorrectly reporting FITS Header Key EGAIN = 0.0 Contact the Nightime Imaging people about getting that fixed. You should try using CCDOps or MaxIm DL Pro to obtain the image. I've attached the data sheet from the chip that I think is in your camera, you may wish to review it. Your telescope (8" RC f/8) with this camera's large 9um pixels may result in some undersampling of your images. A larger scope e.g. 12" f/10 with 3000mm focal length might be a better match. This will show up as "softness", but it will hide guiding errors.
ok I understand. Thanks for the info Is there a way to get better results? for example, at the risk of being silly, turning the ABG into NABG? Changing the sensor?
Have a look at the SBIG CCD694 - a better fit for your scope, or the STC-7 as an alternative. CCD: https://diffractionlimited.com/product/sbig-aluma-ccd694/ CMOS: https://diffractionlimited.com/product/sbig-stc-7/ You might hunt around for an STF-402ME on astromart or something like that. You might be wiser to invest in a larger scope.
It is not possible to replace the sensor. All KAF and KAI series sensors were discontinued by ON Semiconductor in March 2020.
