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ASI2400MC – Red, Green, and Blue Dots & Vignetting Issues

CMOS Troubleshooting
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F. Londe avatar
F. Londe avatar
Last night, I finally had a clear sky to test my new ZWO ASI2400MC camera. However, I noticed numerous red, green, and blue dots appearing in the image, along with noticeable vignetting.

Does anyone know what might be causing this? Any insights or troubleshooting tips would be greatly appreciated!

Binning 1x1
300s exposure
Gain 100
Offset 50
Filter Antlia Quad Band 
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andrea tasselli avatar
andrea tasselli avatar
The R/G/B "dots" are quite simply hot pixels and should go with processing, if done right.  This is quite usual for that generation of chips (I have the same in my FF DSLR camera). As for vignetting, that has nothing to do with the camera itself, but with the imaging train/optics. I can't be surprised, as it is, after all, a full frame camera and expecting a full illumination with anything but either large fast apertures or slow system would be foolish.
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F. Londe avatar
F. Londe avatar
andrea tasselli:
The R/G/B "dots" are quite simply hot pixels and should go with processing, if done right.  This is quite usual for that generation of chips (I have the same in my FF DSLR camera). As for vignetting, that has nothing to do with the camera itself, but with the imaging train/optics. I can't be surprised, as it is, after all, a full frame camera and expecting a full illumination with anything but either large fast apertures or slow system would be foolish.

Andrea,
Thanks for your insight!  Regarding vignetting, I appreciate your clarification,
it makes sense that it's more about the imaging train and optics rather than the camera itself.
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Patrick Graham avatar
Patrick Graham avatar
Doesn't look like you used any calibration frames.   Dark subframes will remove the hot pixels while flat frames will remove the vignetting and any blemishes found in the imaging train. Andrea is right, the suitability of your CMOS sensor and optics will affect the outer edges of your subs.   Use the tool, Astronomy Tools, to determine the compatibility of your set up Of course, you'll need Dark/flats to calibrate the flat frames or Bias frames.  I find dark/flats work best for me with the ZWO cameras.  More work to all this than meets the eye but well worth the effort when you see your results in the final image.  

Clear skies,

Patrick
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F. Londe avatar
F. Londe avatar
Patrick Graham:
Doesn't look like you used any calibration frames.   Dark subframes will remove the hot pixels while flat frames will remove the vignetting and any blemishes found in the imaging train. Andrea is right, the suitability of your CMOS sensor and optics will affect the outer edges of your subs.   Use the tool, Astronomy Tools, to determine the compatibility of your set up Of course, you'll need Dark/flats to calibrate the flat frames or Bias frames.  I find dark/flats work best for me with the ZWO cameras.  More work to all this than meets the eye but well worth the effort when you see your results in the final image.  

Clear skies,

Patrick

Thanks Patrick,

I posted a single FITS file and was curious because this issue never occurred with the AS2600. I was wondering why. I used astronomy tools, and it seems the camera should work well with the RC 12"

Perhaps I'm missing something, but I appreciate your input!

CS,

Fernando
andrea tasselli avatar
andrea tasselli avatar
Light drop doesn't equate to vignetting or at least in the sense of clipping of the marginal rays. From what I can see…
F. Londe avatar
F. Londe avatar
andrea tasselli:
Light drop doesn't equate to vignetting or at least in the sense of clipping of the marginal rays. From what I can see...

Andrea,

That's an intriguing idea! Tonight, I'll be capturing some photons and diving into the image processing and I am curious to see what unfolds.

CS,
Fernando
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F. Londe avatar
F. Londe avatar
andrea tasselli:
Light drop doesn't equate to vignetting or at least in the sense of clipping of the marginal rays. From what I can see...

Andre,

I know this is a bit off-topic, but I’d love to hear your thoughts on the ASI2400MC. Does it make sense to run gain 0 for maximum well depth or gain 140 for minimum read noise, depending on imaging needs?

From what I understand, gain 0 works well for longer exposures, while gain 140 is better suited for shorter exposures or narrowband filters. I’ve also come across discussions where some users experiment with gain 100 in high conversion gain mode to balance dynamic range and noise.

Does this align with your experience? Would love to get your input!

CS,

Fernando
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andrea tasselli avatar
andrea tasselli avatar
There is a very very small difference between running at gain 0 or 140 as far as effective dynamic range (eDR) is concerned and as far as faint signal is concerned, and we all should be concerned about it, then the best compromise between eDR and read-out noise is certainly running in HGC mode and thus @ gain=140 or slightly above it. For the more precise details and thus analysis of the best way forward one would need to run the sensor assessment through SharpCap, but I believe gain=140-145 is kind of optimum in all scenarios.
F. Londe avatar
F. Londe avatar
andrea tasselli:
There is a very very small difference between running at gain 0 or 140 as far as effective dynamic range (eDR) is concerned and as far as faint signal is concerned, and we all should be concerned about it, then the best compromise between eDR and read-out noise is certainly running in HGC mode and thus @ gain=140 or slightly above it. For the more precise details and thus analysis of the best way forward one would need to run the sensor assessment through SharpCap, but I believe gain=140-145 is kind of optimum in all scenarios.

Andrea,
Thank you so much,
That’s a great breakdown! Running HGC mode at gain 140-145 does seem like a great idea and a  sweet spot for balancing effective dynamic range (eDR) and read-out noise.
CS,

Fernando