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zwo asi 183mc oval stars caused by cooler fan?

astrophotography CMOS imaging
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#1 Dave n San Diego

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Posted 19 July 2019 - 08:56 PM

Greetings all, from a long time user who rarely posts.

I recently picked up a new 183 pro.

I have been spending quite a long time trying to focus even with a tight roi   Last night I noticed oval stars appearing at random intervals and found they were all appearing during times when the cooler fan was operating.

Is this just something I will need to work around?

How about just passively cooling the peltier unit?

 

How are you guys focusing?  I like the FWHM aid in BYEOS but there is no support for my new camera.  

I also like APT but i have not been able to get a high enough frame rate (about 5sec / frame) to be able to focus efficiently.

 

Thanks,

Dave

https://www.cleardar...sObCAkey.html?1

 



#2 james7ca

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Posted 19 July 2019 - 10:09 PM

While a malfunctioning fan could cause image blurring I don't think I have ever seen results that indicate that normal fan operation is harmful for DSO work. However, when doing planetary work I never use the camera cooler since millisecond-long exposures are unlikely to be improved with cooling (and you're stacking hundreds if not thousands of subs, so noise isn't as much of an issue).

 

I'm not sure what you mean by "when the cooler fan was operating" as in my experience the fan runs continuously while the cooling is enabled. Is your fan stopping and starting by itself? That would seem odd, but maybe that can happen at very high temperature set points (like close to the ambient air temperature), however, I doubt it (meaning if your fan is stopping and starting then I'd contact the seller or the manufacturer to see what they think). If it is cycling then you might also need to check your power supply.

 

As for focusing, a well-functioning auto focus procedure is probably best (with a motorized focusing unit), but many of us use a Bahtinov mask and focus manually. That said, while a Bahtinov mask is easy to use and pretty reliable I'm not convinced that it will always result in the best focus or even a precisely repeatable point of focus. It's fairly easy and quick to use and it works pretty well but I wouldn't call it completely foolproof (since a user can misjudge the setting). There are, however, a few software-based focusing aids that use a Bahtinov mask and I'd expect that those would be a little more repeatable.

 

Bottom line, if you don't have an auto focus capability then I'd get a Bahtinov focus mask and see how that works out for you.



#3 Marcelofig

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Posted 19 July 2019 - 10:15 PM

The fan shouldn't cause oval stars. While the camera/fan is running (but not taking pictures) touch it with your hands, you should not feel any vibration. If it vibrates, the fan may have a broken blade and that can cause problems.

 

If this is the case, ZWO may send you a replacement. But it's quicker to buy one and make the replacement. It's a simple PC fan that costs about $10.


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#4 james7ca

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Posted 19 July 2019 - 10:29 PM

...While the camera/fan is running (but not taking pictures) touch it with your hands, you should not feel any vibration. If it vibrates, the fan may have a broken blade and that can cause problems...

While a fan could certainly be "bad" and cause vibration issues I'd be a little cautious to say that "you should not feel any vibration." Sensitive fingers can be, well, awfully sensitive to very minor vibrations which could be no problem at all.

 

If in doubt take a series of short-exposure images with and without cooling on a night with good seeing and reasonable temperatures and then run something like PixInsight's SubframeSelector and look at the FWHM and eccentricity measurements. You're going to see frame to frame variation in both sets of images, but any trend with one or the other (being consistently worse) should give you concern. Oh, try to take the images at near to the same temperature, meaning a fairly high set point temperature (low offset).



#5 OldManSky

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Posted 19 July 2019 - 10:42 PM

I focus using HFR measurements in NINA, and with a Bahtinov mask.

NINA's blazing-fast downloads make for a nice full-frame focusing experience ;)

 

The post above was right, if the cooler is on the fan should be constantly running.  If yours isn't, that's an issue.  If it is, it's not the fan causing oval stars...I'd suspect guiding first.



#6 H-Alfa

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Posted 20 July 2019 - 08:35 AM

Hello,

Here you can find more information about this issue.

https://r.tapatalk.c...36&share_type=t

Star ovalization with ASI071MCP... PSU or fan issue?

Enviado desde mi ANE-LX1 mediante Tapatalk

#7 H-Alfa

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Posted 20 July 2019 - 08:37 AM

And here (this is the first that I saw regarding this subject)

https://www.cloudyni...fwhm-increases/

Enviado desde mi ANE-LX1 mediante Tapatalk

#8 apophisOAS

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Posted 20 July 2019 - 01:03 PM

With my ZWO ASI183mm Pro ,i Bin 4x4 and 2 seconds exposure in live view to focus no problem.When it looks right i save the fits as a jpeg as its clearer to see the bhatinov image.
HTH
Roger




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