Fri, 12/11/2020 - 07:54
I am thinking to get the new QHY294 M Pro to replace my Atik 383L. As I have no experience with the new CMOS sensors I wonder whether they are good for photometry. I am particularly concerned about the amp glow. Although it can be reduced with dark frames I have learned that it cannot be completely eliminated and I wonder if that can impact the photometry.
Hi Gianluca,
I'm also looking at the QHY294M, as a replacement for my STT-8300 with a failing board (again!). This camera is certainly an appealing option: 14-bit AD, great quantum efficiency (~90% vs. ~60% for the STT-8300), good size, and decent full-well capacity. However, I'm also a bit concerned about amp glow, as well as all of the other unknowns (for me, anyway) with CMOS detectors. The amp glow, at least, looks like it's not too big of an issue - and is supposed to be pretty consistent at the same temperature, exposure and bias setting. My understanding is that the biggest issue is that the glow may not be linear, certainly not when changing bias values, so you should make darks with the same settings as the light images (i.e.: don't use scaled dark frames).
Several of the BSM scopes are now using the QHY183M, and the data I've gotten from them via AAVSOnet has been very good. I believe a few AAVSOers are using QHY600s and getting good results. However, does that mean that every mono CMOS camera will be suitable for photometry?
Arne posted a comment here several months ago that he was evaluating several CMOS cameras, including the ZWO ASI294 that uses the same chip as the QHYCCD. Hopefully, he'll weigh in on what he's found so far.
Shawn
Other than Meade & QHY which I also use, ZWO have become a favorite and are certainly comparable in quality and price. It's only a matter of determing which sensor. I am now looking at the ASI6200MM-P with the IMX455... I currently use the ASI071MC-P, 1600MM-P, 462MC, 224MC, 120MM-S & 120MC-S. Amp glow was addressed in the 1600MM Pro along with other issues i.e. dew, etc.
I finally got a chance to watch the AAVSO "Focus on CMOS" webinar last night. Arne mentioned the ASI294 but didn't have any detailed information on it. However, he had several links to other references, including an analysis by Christian Buil: http://www.astrosurf.com/buil/asi294mm/. An interesting read, and to me, it sounds like the ASI/QHY294 should be "just as good" for photometry as the 183 that has been used on the BSM scopes for many months now. The 294 has the added advantages of a greater dynamic range and larger chip. I'm still undecided whether to spend ~$1100 getting my STT-8300 fixed or putting the money towards the 294. It seems like CMOS technology is improving rapidly, and waiting a year or two might pay off.
Shawn
I have learned that there is a new model from QHY the 268 mono that has a better dynamic range (native16 bit) and a bigger chip (APS-C size) compared to the 294. I have also learned that there is a short back focus version (6.7 mm vs. 17.5 mm standard) that appears to be more suitable for using it with filter wheels, OAGs, spectrometers etc. QHY offers the same short back focus version for the 600 model (full frame). The problem is that they state that as the sensor is closer to the glass window there is a greater risk of getting condensation regardless of the anti-dew heater that is built in the camera. 6.7 mm of back focus would be perfect to me as it allows for more flexibility but I am concerned about the dew. Is that going to be an issue? Are there AAVSO observers that happens to know more about that?
Gianluca
Hi!
I bought brand new ASI294MM Pro (same sensor, main competitor of QHY294M) before New Year and I`m in progress of examination it now.
I would say that amp glow is moderate. This is a 60s calibrated dark, taken with -10c, stretched in PixInsight. The actual pixels values are very low, ~0.0001.
And this is a stack of ~30 calibrated subframes (each 60s). It looks like amp glow was complete removed by dark frame:
Alexey,
Thanks for the images. The stacked light image looks very clean: no sign of the amp glow after removing the dark. It seems like the 294MM will be a good choice. The prices and QE are both attractive.
Shawn (dks)
Hi all,
I just got a ZWO ASI 294mm Pro and was wondering (since the two hardware binning modes are a bit special for CMOS sensors) which capturing software people are using here with the ZWO or QHY 294 mono cameras.
I'd also like to hear opinions on pixel defect mitigation for this sensor. I'll probably use this thing in 11 Mpix readout mode most of the time , so using the hardware 2x2 binning. But I would think that this could mask pixel defects and maybe it's better to first create a defect map in un-binned mode and (to be on the conservative side) transform it to a 11Mpix defect map by marking all pixels bad that have at least one bad pixel per binned 2x2 pixel group?? Is that too pedantic perhaps?
Clear Skies
HB