Re: First light for a new camera


Luca Marinelli
 

 As I mentioned above, I have been imaging with the ASI294MM Pro since the end of December. It replaced a ASI1600MM Pro on a TS ONTC 10in f4 Newtonian astrograph.  These are the main differences between the two cameras as I see them:

ASI1600MM Pro:

Pros:

- It has been around for a long time, everyone can help you if you run into trouble

- Less expensive

- Very little amp glow even for narrowband imaging

- Data calibration is robust and straightforward


Cons:

- It has been around for a long time: it may get discontinued in the not too distant future. the ASI294MC took the place of the ASI1600MC.

- Microlensing artifacts around bright stars are obnoxious and difficult to eliminate (this is really an issue only around magnitude 2-3 stars or brighter)

- QE is modest (~50% @ Ha)

- 12bit ADC

 
ASI294MM Pro:

 Pros:

- New sensor with probably long life in front of it

- Two pixel sizes in one camera (2.3um, 4.6um)

- Extremely high QE (it's an amazingly sensitive camera, 80% @ Ha)

- very low noise and high dynamic range when high gain mode kicks in
- no microlensing artifact

- 14bit ADC instead of 12bit

 

Cons:

- More expensive than ASI1600MM

- Calibration is a bit trickier and requires some getting used to (flats have some swirly patterns that some people have had trouble with)

- Amp glow is pretty significant. It calibrates out well but again it requires flawless calibration practice to ensure high quality data is produced.

 
Low read noise combined with high sensitivity and 14bit ADC of this camera makes it compelling vs the older 1600MM. The questions Roland asked about speed compared to CCD cameras comes down to two factors:

1) QE: How sensitive is the camera? In comparison to the numbers above, the FLI ML16200 has QE of 45% @ Ha - quite a stark difference.
2) Read noise: Low read noise is meaningful in relation to noise from sky glow. That's why with CCD cameras subexposure times for narrowband imaging can be 20, 30 minute or even longer. With the ASI294MM even imaging faint targets I have found that I can achieve optimal exposure levels for narrowband imaging with 3nm filters under Bortle 5 skies in less than 8 minutes per sub. This means that I can guarantee not to lose any SNR efficiency in image integration and accumulate SNR as fast as total integration time. 

I recently completed an imaging project of an extremely faint planetary nebula (HFG1) that I started in September 2020. I collected most of the 82 hours of data with an ASI1600MM Pro but during the last month of data collection I switched to the ASI294MM. For the purpose of illustrating differences in sensitivity of the two cameras, I integrated 20x6 minute subexposures of OIII  signal from each of the two cameras. Pixel size is a bit different (3.8um vs 4.6um) and I registered all the images to the higher-resolution ASI1600MM data before image integration to try and reduce the effect of bigger pixels in the ASI294MM on image SNR. You can see the results of the experiment here:

https://astrob.in/tbilkr/B/

I am also imaging with an ASI6200MM Pro and while the sensitivity is comparable to the ASI294MM Pro (IMX455 sensor), the noise profile is even more favorable with lower read-noise, 16bit ADC, and no amp glow. The new APS-C sized IMX571 is expected to have similar characteristics.

--Luca


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