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Old 16-09-2013, 12:21 AM
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who images with the cooling fans on?

Hi All,

So, who images with the cooling fans running? who runs them at the start to cool things down then turns them off? I think Ive noticed worse star shapes with them running but will have to confirm this.

thanks
Josh
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Old 16-09-2013, 06:20 AM
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lazjen (Chris)
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I'm probably not that much help here, but I run them all the time. If they're affecting the image in anyway, i'm not sure what to look for - I assume it might make things be a bit softer focus, perhaps?
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Old 16-09-2013, 06:44 AM
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I do... not the factory fan though.
My Bintel 200mm f/4 came with a cooling fan screwed to the bottom of the primary cell - it would vibrate the scope mercilessly... I relocated the fan onto a piece of foam that is velcroed to the tube via another piece of foam... not pretty, but keeps my mirrors dry, and doesn't affect focus at all....
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Old 16-09-2013, 07:50 AM
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I run them continuously. I'd have to check if there is a difference on or off in terms of vibration. I suspect no effect. But there is certainly a softening effect from mirrors being not at ambient and also perhaps from a boundary layer forming on the mirror surface.

I find if the mirror is 1C different focus will be soft and it sharpens considerably when the mirror and air per the temp sensor is .1C different.

Greg.
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Old 16-09-2013, 07:54 AM
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Use the fans. I have not done many images with the scope that has the fans but can say I have not notices any blurring. Seeing and mirror heat discharge is more likely to cause issues with the images rather than the fans being on.
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Old 16-09-2013, 10:40 AM
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thanks guys,

last night i noticed, when the fans were running, from the few star images i took there would be slight bloating of the star. Then upon turning them off, the star shrunk slightly in size. there were only seconds between having the fans off an on so not enough time to change the mirror temp which was within 0.2 - 0.3 degrees C of ambient temp.

Ill have to do a more extensive test on this.

thanks
Josh.
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Old 16-09-2013, 10:59 AM
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I think the fans could be a red herring Josh, but as you say more extensive tests are needed to validate this. I would certainly keep them on. I assume the EFA kit and fans allow for variable speed? Perhap run them at 25% power once you've hit thermal equilibrium. A tube creates a concentrated airflow so you wouldn't need to run them high.

I'm not sure how advanced the EFA kit is, but with the RCOS TCC, the 'auto' setting measures the various temperature sensors and calculates the optimal fan speed. It does this over the night so the optics can be within 0.1 degrees (configurable) of ambient.
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Old 16-09-2013, 11:03 AM
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thanks Jase.

Quote:
Originally Posted by jase View Post
I think the fans could be a red herring Josh,.
Do you mean something else is causing what im seeing?

the EFA kit has 3 settings for the fans - on, off and auto (meaning on when the mirror is within a set temp range), but the speed is set when they are on. maybe i could mention it to PW about variable fan speed.

thanks
Josh

Last edited by Joshua Bunn; 16-09-2013 at 11:16 AM.
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Old 16-09-2013, 11:23 AM
jase (Jason)
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Quote:
Originally Posted by Joshua Bunn View Post
thanks Jase.


Do you mean something else is causing what im seeing?

the EFA kit has 3 settings for the fans - on, off and auto (meaning on when the mirror is within a set temp range), but the speed is set when they are on. maybe i could mention it to PW about variable fan speed.

thanks
Josh
Yes, Josh. I think the problem being related to the fans are a long shot. The numbers are at least against you. There are no doubt numerous 12.5" Planewaves out in the field running fans full time without issue. If it were a specific fan type causing vibrations or similar, then I'm sure Planewave would have heard more about this and done something about it. This could be an isolated case, but as you suggest more testing is required.
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Old 16-09-2013, 11:26 AM
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Thanks Jase, i hope your right.

Quote:
Originally Posted by jase View Post
as you suggest more testing is required.
Yes.

Josh.
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Old 16-09-2013, 08:09 PM
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I run my fans permanently on auto (Ceravolo 300) and have never noticed any issues. I can't even hear them over the jet engine noise of the fans in my Apogee Alta U16M camera
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Old 16-09-2013, 09:46 PM
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Fair point Rick, thanks.

Josh
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Old 17-09-2013, 05:47 AM
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+1 . Fans on.
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Old 17-09-2013, 10:55 AM
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Always run my RC with fans on. Makes a difference.
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Old 17-09-2013, 10:18 PM
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Hi Josh,

When the primary is chasing the ambient temperature as the outside temp is falling, if the difference is great fans will definitely help till the primary stabilises. I found by chance when completing a focus run that monitoring a defocused star under consecutive shooting allows you to see the deformation of the star without the fans on. When the variation is great between the primary temp and ambient, in my case > 1.5c, there is a slight shimmer that worsens with the greater difference. The donut deforms without the fans on. Try it next time you have a fast cool down in ambient temp relative to the primary temp. It's very noticeable. Just manually switch the fans on and off between the subs.

If you do not have primary heating, there is also the argument that if your fans draw the air in from the front and out the back, that they will draw dew in at an accelerated rate.

Regards

Steve
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Old 18-09-2013, 01:03 AM
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Thanks Steve.

tonight i had a chance to test this some more and there's no problem. The fans on actually made the star a little sharper, so my observation the other night was incorrect. I should do some more thorough tests before posting hey.

thankyou all for your replies.

Josh
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