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Old 02-02-2020, 09:52 AM
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ZWO versus QHY

I have been following the threads on Cloudy Nights about the new 61mp ZWO6200mm and the QHY600.

Looking at the websites of both I can see why there is interest. Prior to this model all their models except it seems for one recent one are all 14bit like a DSLR.

Also the largest sensors in mono have been micro 4/3rds size - about 17 x 13mm, which is quite small. The APSc and full frame sensors up to now are all one shot colour and 14 bit.

Some details are quite sketchy like cooling up to 35C from ambient but it does not say if its regulated like a FLI or SBIG or QSI camera. This affect darks etc. I assume it is but its not stated.

Also the assumption that only 30C drop in temp is plenty or -5C is plenty for these sensors. Again a big assumption as dark current is not the only thing low temperatures fix. Banding is another which I see can occur with the ZWO at room temperature (I assume, perhaps incorrectly, that is true for QHY as well).

If you have evaluated these 2 brands what are the pluses and minuses between a ZWO and a QHY?

Greg.
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Old 02-02-2020, 11:52 AM
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Peter Ward
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QHY are temperature regulated. Not to the same precision as SBIG (who have a patent on keeping the chamber temp to 1/100th of a degree or so) or FLI.

i've found it is a little tricky to estimate just what delta t you can get with a QHY, as the power required seems very nonlinear. But as the chips are thermally "quiet", a set point of -10 is more than adequate.
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Old 02-02-2020, 12:20 PM
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Quote:
Originally Posted by Peter Ward View Post
QHY are temperature regulated. Not to the same precision as SBIG (who have a patent on keeping the chamber temp to 1/100th of a degree or so) or FLI.

i've found it is a little tricky to estimate just what delta t you can get with a QHY, as the power required seems very nonlinear. But as the chips are thermally "quiet", a set point of -10 is more than adequate.
Except for the fact that some owners are reporting banding at warmer temps and it becomes far less when cooled.

High cooling also reduces lines in CCDs so banding it would seem may disappear all the way with stronger cooling.

I also wonder about how stable their temperature regulation is. It could affect darks but then again it may be unnecessary to use darks like it is with the Sony ICX694 and other sensors.

Powerful, stable cooling may be less important with these sensors but I can see it would still be nice to have too much cooling rather than not enough.

Perhaps this sensor will come out within a year from other camera makers like SBIG, FLI, Moravian.

Perhaps its not even an issue but its a bit early to tell and perhaps it affects one brand more than the other.

On Cloudy Nights I see posters talking about using -5C. But that's in their Northern Hemisphere winter. Try getting that with 30-35C delta in an Aussie summer night. You may end up at +5C which may not be anywhere near enough.

Greg.
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Old 02-02-2020, 12:22 PM
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I would say that they are all "Regulated" even older cameras show that, it is just a matter of how tightly they are regulated. All the cooled cameras I have seen look to me to be temperature regulated by a PID system, the bigger the difference from the setpoint, the bigger the steps in cooling power each time and then the last little bit takes longer as it takes time to integrate the smaller error to drive a correction signal.

I would expect the cooling versus power to be non linear, at my guess the peltier coolers will be driven by a PWM signal and the cooling power percentage will be the PWM duty cycle, from there it is just like your aircon at home, the amount of cooling power increase required per extra degree of temperature delta from ambient increases degree by degree.

Last edited by The_bluester; 02-02-2020 at 03:58 PM.
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Old 03-02-2020, 09:21 AM
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Anyone care to comment about their experiences good or bad with either ZWo or QHY?

QHY were originally one of these low cost, poor quality manufacturers who have raised themselves up to make what look like some good products.

Is that what owners have experienced or do they have issues?

Greg.
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Old 03-02-2020, 10:07 AM
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Having owned a number of QHY and ZWO cameras, my generalised comment would be that QHY produce better mechanical products (more refined build quality) but ZWO have more stable drivers.
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Old 03-02-2020, 10:47 AM
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I can only comment on ZWO and only on the one camera, an ASI294MC Pro whigh I have been using for about a year.

The build quality seems OK to me, the only issue I have had with it at all has been a little moisture creeping in which I have not yet resolved by baking the dessicant. I am going to try again soon or maybe even get a dessicating cabinet and open the sensor chamber up for a while inside it. It has not troubled me in imaging but as it first cools you get a tiny bit of frosting on the sensor which then disappears over time. Imaging wise it has never proven a problem but if you jump in, cool the cam and go to shoot some flats it has been an issue.

The drivers have been dead stable since I have had it.

The only critique I would put on it from a mechanical standpoint is that with an M42 threaded connection it is obviously aimed at the lower end of the market where other cameras have screw threads in the mounting faces to allow for a solid connection to a guider or filter wheel without messing with spacers to try to get the orientation "just so" The new and dearer cams seem to be addressing that.

I am happy enough with it to consider a new ASI2600 or if the budget stretches, a 6200.
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Old 03-02-2020, 07:08 PM
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Quote:
Originally Posted by The_bluester View Post
I can only comment on ZWO and only on the one camera, an ASI294MC Pro whigh I have been using for about a year.

The build quality seems OK to me, the only issue I have had with it at all has been a little moisture creeping in which I have not yet resolved by baking the dessicant. I am going to try again soon or maybe even get a dessicating cabinet and open the sensor chamber up for a while inside it. It has not troubled me in imaging but as it first cools you get a tiny bit of frosting on the sensor which then disappears over time. Imaging wise it has never proven a problem but if you jump in, cool the cam and go to shoot some flats it has been an issue.

The drivers have been dead stable since I have had it.

The only critique I would put on it from a mechanical standpoint is that with an M42 threaded connection it is obviously aimed at the lower end of the market where other cameras have screw threads in the mounting faces to allow for a solid connection to a guider or filter wheel without messing with spacers to try to get the orientation "just so" The new and dearer cams seem to be addressing that.

I am happy enough with it to consider a new ASI2600 or if the budget stretches, a 6200.
If you baked the desiccant properly and it is still doing it that sounds like an air leak in the chamber.

Try getting some wine saver argon and put some argon in it. A wine saver off ebay costs about $30.

Greg.
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Old 03-02-2020, 08:03 PM
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I was thinking about doing that. It has been fairly humid around here so it is quite possible that I have allowed as much moisture in while the chamber was open as I removed by baking the pills. I did have a couple of seriously dew prone nightsover the winter, so bad that one night before I had a heater strap for it my little ED72 drew moisture in between the elements of the objective! Given the air in the chamber would contract as it cools I suppose it might find any poorly sealed spot on the O ring.


And yes to the wine saver idea, I was thinking of doing just that, a pity they don't fit purge ports to these things.
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