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ZWO ASI 485 - QHY 485

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#1 vilchez

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Posted 15 October 2021 - 03:52 PM

I was reading about the new ZWO ASI 485MC and when comparing with the QHY 485 I have seen that the color sensitivity curves are different, supposedly it is the same cmos, who is wrong?

 

VRkTNF1.jpg

OALBKda.jpg

 

 

 

 

ZWO ASI: https://astronomy-im...roduct/asi485mc

 

QHY: https://www.qhyccd.com/qhy5iii485c/


Edited by vilchez, 15 October 2021 - 03:53 PM.

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#2 rgsalinger

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Posted 15 October 2021 - 04:10 PM

Chances are that one is "relative" and one is "absolute" - actual QE. Note that the shape is identical and these things are determined by the chip and not really the electronics. 

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#3 Tulloch

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Posted 15 October 2021 - 04:47 PM

They were different for the 462MC also - note especially the blue channel at higher wavelengths, the ASI website shows the blue channel at 20% at 700nm, while the QHY website shows it at a level of less than 5% at 700nm.

 

There should be no difference in these curves at all, and they should be sent out by Sony, not relying on ASI and QHY to release them, especially when they are significantly different...

 

ASI - https://astronomy-im...t/asi462mccolor

 

ASI462-QE-curve.png

 

QHY - https://www.qhyccd.com/qhy5iii462c/

 

QHY 462 curve 20200620044746606.png

 

Andrew


Edited by Tulloch, 15 October 2021 - 04:49 PM.

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#4 Ittaku

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Posted 15 October 2021 - 05:35 PM

I've got the ASI485MC, and judging by my red/blue settings I'd hazard a guess that the QHY "relative response" curves are more relevant to us.



#5 Tulloch

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Posted 15 October 2021 - 06:11 PM

I guess it was probably too good to be true that the red/green/blue responses would have been more or less identical as shown in the ASI curves, but there is a massive difference in the IR responses.

 

Unless there's something strange about the transmission through the AR window on the ASI version that slightly blocks longer wavelengths, I can't understand the difference between the two... confused1.gif



#6 Ittaku

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Posted 15 October 2021 - 07:01 PM

I'm just as baffled, and tempted to remove the AR window just to see how it affects sensitivity.



#7 Tulloch

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Posted 15 October 2021 - 09:15 PM

Well, assuming it's just one of these, it shouldn't affect the visible - but will have an impact upon IR.

https://astronomy-im...dow-asi-cameras



#8 Ittaku

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Posted 15 October 2021 - 09:54 PM

Yeah I recall the spectra but something still doesn't add up.

#9 dcaponeii

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Posted 18 October 2021 - 01:03 PM

Until you scale the axes to be the same physical dimension you can't really compare the curves "visually" by inspection.  I think in both cases if you scale the axes to the same dimensions they would superimpose quite well onto one another.  Looking at the minima and maxima they do not appear to be appreciably different from one another.  It appears the in the second comparison set of data QHY is interpolating the data (hence the dashed lines) and thus cannot display the detailed variations present in the ZWO data.  Of course maybe it's the "chinese whispers" again.


Edited by dcaponeii, 18 October 2021 - 01:14 PM.


#10 Ittaku

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Posted 18 October 2021 - 03:49 PM

  It appears the in the second comparison set of data QHY is interpolating the data (hence the dashed lines) and thus cannot display the detailed variations present in the ZWO data. 

The dashed line is meant to be what is blocked by an IR blocker, it isn't an interpolated data line.


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#11 Tulloch

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Posted 18 October 2021 - 05:07 PM

Until you scale the axes to be the same physical dimension you can't really compare the curves "visually" by inspection.  I think in both cases if you scale the axes to the same dimensions they would superimpose quite well onto one another.  Looking at the minima and maxima they do not appear to be appreciably different from one another.  It appears the in the second comparison set of data QHY is interpolating the data (hence the dashed lines) and thus cannot display the detailed variations present in the ZWO data.  Of course maybe it's the "chinese whispers" again.

Well, I tried that, and here are the results. The 462 data is easy as both graphs have been scaled to show the maximum QE in the IR at 100%. The curves look pretty similar, except in the blue and green channels bleeding into the red.

 

ASI462 vs QHY462 curves.jpg

 

The 485 is more problematic, QHY have normalised the red peak to 100% and scale everything off that. Matching the two curves to show is at 100% give this - they are pretty different imho.

 

ASI485 vs QHY485 curves.jpg

 

Andrew


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#12 dcaponeii

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Posted 18 October 2021 - 05:54 PM

Well, I tried that, and here are the results. The 462 data is easy as both graphs have been scaled to show the maximum QE in the IR at 100%. The curves look pretty similar, except in the blue and green channels bleeding into the red.

ASI462 vs QHY462 curves.jpg

The 485 is more problematic, QHY have normalised the red peak to 100% and scale everything off that. Matching the two curves to show is at 100% give this - they are pretty different imho.

ASI485 vs QHY485 curves.jpg

Andrew


Certainly looks that way. Odd. Does anyone know the details of how the data itself is obtained. Are they sending a specific wavelength onto the camera chip and recording the response? I guess they could isolate specific wavelengths with diffraction gratings? If the incident light is slightly different between the two data sets that could explain it?

#13 Borodog

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Posted 18 October 2021 - 07:29 PM

It will have been specified in a measurement standard.
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#14 GSBass

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Posted 18 October 2021 - 09:18 PM

I can vouch for the 485 having alot of green :)…. But it does ok and is a nice size chip for the money, it’s my primary dso cam right now



#15 CPellier

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Posted 19 October 2021 - 03:38 AM

This is weird. One of the two, in each pair, must be wrong, especially for the IMX485 - those are two completely different issues of a so called same sensor.

As experienced in "field" imaging, the ZWO curve for the 462 looks more coherent with the results, with less color separation than for the IMX224 in the images.


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#16 dcaponeii

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Posted 19 October 2021 - 07:25 AM

It will have been specified in a measurement standard.

Yes for sure but I was wondering if they were using different standards since there is no reference given to an outside certification organization they could be using internal standards that are not the same.  Although the chips in principle are identical differences in assembly of the camera's (specifically thinking about the transmission windows) might be different in such a way that the sensitivity of the camera at specific wavelengths is being affected.



#17 GSBass

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Posted 22 October 2021 - 07:46 AM

I leave it up to others to explain in depth meaning of graphs and charts, … mostly I just use the written comparisons to previous chips I am familiar with, when they said for example the 464 was equivalent to 462 that’s really all I needed to make the purchasing decision…. If a new chip came out they said was equivalent to the 485 I might hesitate… not because it’s a bad chip… it’s just that I know it could be better…. It actually surprised me zwo released the chip, I expected they would skip it as long as it took them to get around to it

Yes for sure but I was wondering if they were using different standards since there is no reference given to an outside certification organization they could be using internal standards that are not the same.  Although the chips in principle are identical differences in assembly of the camera's (specifically thinking about the transmission windows) might be different in such a way that the sensitivity of the camera at specific wavelengths is being affected.


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