ZWO ASI 533MM-Pro CMOS Camera for Photometry?

[Mr Ian David Sharp]

Hi all,

I know there have been various discussions on using CMOS cameras for photometry, but I like to find out if anyone has used the ZWO ASI 533MM-Pro USB 3 Cooled Monochrome Camera for photometry.

I ask because my SX694 TRIUS Pro CCD camera keeps on failing and has been back for repair 3 times (the head amp, apparently). It came back last week and failed again on the second night of usage! BTW, I have another one of these in Spain which works very hard and has been faultless for 2 years or so.

One of the things that attracted me to the IMX533 chip, when looking at CMOS cameras, is that its size of about 11.5mm x 11.5mm is quite similar to the SX694 and this means I can still use my existing 1.25″ filters without much vignetting. It is also 14-bit, well cooled, maximum full well of 50,000, so what’s not to like?!

I also feel like I need to take the plunge from CCD to CMOS for photometry as CCD cameras will be very hard to obtain in the not too distant future.

I could but the ATIK 460EX CCD which is the equivalent of the SX694. I have found ATIK cameras to be very reliable. However this is a full £1000 more expensive than the ZWO!

I would value any opinions!

Ian.

[Kevin West]

Hello Ian,
I posted this on AAVSO last month ad Arne Henden replied with this. It may be of use in your quest.
Regards
Kevin

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CCD or CMOS

Hi Kevin,

Congratulations for getting back into photometry!

Here are some pros and cons.

CCD pro

usually larger pixels

decent read noise

decent QE

always 16-bit pixels

can be inexpensive if purchased used

CCD con

few new cameras available, so you may have trouble getting service in the future, depending on the vendor

for the same pixel size, higher read noise and dark current than a CMOS camera (though these are really not important for wide band photometry since the sky or star noise will dominate)

new cameras tend to be more expensive for the same sensor area

CMOS pro

lower read noise, lower dark current, higher QE than CCD

can take very short exposures, not limited by shutter speed

lower cost than equivalent CCD sensor size

CMOS con

no mechanical shutter, so darks require covering things and/or blank filter taking up a filter wheel slot

random telegraph noise, which requires multiple images and stacking to fully remove (though low level, and sky/star noise will dominate)

some early generation sensors (such as the IMX183) have amplifier glow

some early generation sensors (such as the IMX183) are 12-bit only

So both sensor types have good points and bad, though most of the “bad” is mitigated by taking exposures through wide-band photometric filters like Johnson/Cousins or Sloan. If I were starting out today, I’d probably select a camera that uses the IMX-571 sensor, such as the QHY268 or the ASI-2600, as this sensor is the best CMOS value right now, and you can use 1.25″ filters with some corner vignetting (or 36mm filters with no vignetting).

Arne

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[Dr Andrew Smith]

Hi Ian, I don’t have info on that model camera but I used a ASI 294 MM Pro for exoplanet photometry. My results are in the AVSO database under SAJB and compare well if not better that those with CCDs. Where NASS has added them to their database the results are comparable.

Hope this reassures you about CMOS.

Regards Andrew

[Mr Ian David Sharp]

Many thanks Andrew and Kevin,

I’m coming around to the idea!

Best Regards
Ian.

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