ZWO ASI6200 strange problem

[Horwig]

This is a stretched 100% crop of the centre of a one second exposure flat frame, and its fixed pattern on all the flats captured in this session, lights captured the day before are fine, am going to investigate more, but anybody come across anything similar?

Huw

[Ouroboros]

27 minutes ago, Horwig said:

This is a stretched 100% crop of the centre of a one second exposure flat frame, and its fixed pattern on all the flats captured in this session, lights captured the day before are fine, am going to investigate more, but anybody come across anything similar?

Huw

Obvious and maybe stupid question. Have you looked at the camera? It’s not moisture condensed on the front face is it? 

[Horwig]

Don't think so, camera was indoors. Just tried it again now, same problem, powered down, re-connected and powered back up, problem has gone.

Hate faults like this, prefer it to work or fail entirely, not some intermittent fault

Huw

[Horwig]

Dis-connected the camera, left it to warm up for a while, and guess what, patterning is back.

Camera is powered off battery, supply is reading 12.5V at 1.5 Amps, nothing else connected.

Reckon I'll raise this with FLO, let's see if they have had heard of anything similar

Huw

[Horwig]

2 hours ago, Ouroboros said:

Obvious and maybe stupid question. Have you looked at the camera? It’s not moisture condensed on the front face is it? 

Grovelling apologies, yes, a far from stupid question! Patterning happened when cooling approached about 80%, and then a small spot of condensation was visible on the cover, switching cooling off removed the patterning in a few seconds.

I have cooling set to -10c in one minute, changed this to two minutes, but the cooling still reaches 80+%. Naturally, this is indoors, outside I doubt it will run as hard, ergo, clean lights, compromised flats.

Thanks again.

Huw

[Ouroboros]

No worries. Does this camera have the antidew feature …. can you switch it on?  The ASI2600 does and I switch it on within the ASIair interface. 

[Horwig]

9 minutes ago, Ouroboros said:

No worries. Does this camera have the antidew feature …. can you switch it on?  The ASI2600 does and I switch it on within the ASIair interface. 

Interestingly, yes antidew is on, obviously it does not cope well with 80% cooling from an ambient 20C

Huw

[Ouroboros]

12 minutes ago, Horwig said:

Interestingly, yes antidew is on, obviously it does not cope well with 80% cooling from an ambient 20C

Huw

Mmmmm.  What do you have the camera connected to? I have had a similar problem with a DSLR camera attached to my Newtonian, which inevitably exposes the camera front face to a large mass of air of course. I have not had the problem when connecting my cooled ASI2600 to my refractor + flattener. The latter exposes the camera to a much smaller volume of air. 

[Ouroboros]

I’m not sure why the 80% you mention would make any difference. That’s just a measure of how hard the Peltier is cooling isn’t it? What will make a difference is the temperature the camera is cooled to and the amount of moisture in the air in front of the camera. 

[symmetal]

My ASI6200 does the same when cooled below 0C. It is condensation forming on the sensor. The anti-dew heater just heats the protect glass on the front of the camera to prevent dew forming on the front surface, but has no effect on the sensor dewing up.

It is there on the lights too but is very difficult to see on a single exposure.

Like my ASI071 it is not fully airtight inside so the internal dew tablets get saturated over time. Changing them is only a temporary fix as it'll happen again fairly quickly depending on how airtight it isn't.

When not in use, storing the camera in an airtight food container with a big pack of desiccant will help. Removing the accces port screw under the round black sticker when placed with the desiccant will help dry out the internal tablets quicker.

My ASI2600 doesn't have this problem and has never dewed up even when outside for weeks on end.

Zwo will reseal the internals under guarantee if returned to them I believe.

I also only cool it to 0C now to save the problem reoccuring. The improvement in dark current from 0C to -10 is very small and not worth worrying about in reality.

Alan

[Ouroboros]

@symmetal That’s a good point. Is moisture forming on the front cover plate of @Horwig’s camera or the sensor? 

[symmetal]

Just now, Ouroboros said:

@symmetal That’s a good point. Is moisture forming on the front cover plate of @Horwig’s camera or the sensor? 

If it was the camera front cover plate it would be significantly out of focus.

Alan

[Ouroboros]

I tend not to cool my camera below 0° either after watching the YouTube lecture on noise by Robin (sorry can’t recall his second name).  Mr SharpCap.   As you say, there’s not much point. 

[Ouroboros]

2 minutes ago, symmetal said:

If it was the camera front cover plate it would be significantly out of focus.

Alan

Yep. Good point. 

[symmetal]

If you plot the dark current figures given in the manual on a linear graph rather than the exponential one supplied you can see the actual effect of cooling it below zero is minimal when  compared to the other forms of noise present in the image.

I use it on my RASA and noticed that when doing a collimation test the heat rising from the peltier cooling causes a significant shimmer on the doughnuts above the camera which is much worse if cooled more, so I thought the increase in 'seeing' distortion when below 0C has a far bigger effect than the slight increase in dark current at 0C. 🙂

Alan

Edited January 28, 2023 by symmetal

[Horwig]

Thanks both. I've only had the ZWO two years, and two very bad years for imaging, constant cloud cover. Just four usable imaging runs in the whole period. My previous camera was an SX model, and that dewed up something terrible, the whole of the centre of the image was a soft pudding of defocus, the problem on the ZWO is much more subtle, a barely discernible patch, and I can't really tell if it's on the slip cover or the window, but it's tiny, no more than 3 or 4 mm dia.

The camera is connected to either a reduced refractor, a Newtonian with corrector, or a stills lens, in all cases the air within the filter wheel is the greatest volume, I used to run the SX with a desiccator within the filter wheel.

I was under the impression that the rate of cooling was influencing the creation of dew, hence slowing down the cooling was the way to go, but maybe I was wrong.

I remember watching that youtube lecture, and good it was too.

The noise from the ZWO is minimal, haven't measured it, but a single sub looks as good as some stacks I've had from the SX. Maybe reducing the cooling is the way to go.

Now if only I had some clear skies to experiment under.

Huw

[andrew s]

I had a similar issue and was told by ZWO on their forum it was due to ice crystals. 

The cure for me was to cool the sensor slowly.  I run a script that cools it to 0 then waits 2mins then in 1 degree steps down to -10 with a two minute wait each step.

Regards Andrew 

[Whirlwind]

17 hours ago, Horwig said:

I was under the impression that the rate of cooling was influencing the creation of dew, hence slowing down the cooling was the way to go, but maybe I was wrong.

No it's nothing to do with rate of cooling (other than how quickly it will form).  It is at a simplistic level a combination of humidity and differential temperature.

If you have high humidity you need less differential temperature for dew to form.  If you've had some particularly wet weather the humidity will be higher so it is more likely to form on a cooled surface. 

[Adam J]

 

On 28/01/2023 at 20:32, Ouroboros said:

I’m not sure why the 80% you mention would make any difference. That’s just a measure of how hard the Peltier is cooling isn’t it? What will make a difference is the temperature the camera is cooled to and the amount of moisture in the air in front of the camera. 

More to the point 80% power is a indication of high temperature differential, higher temperature differential  =  more likely that dew will form. 

Adam