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Cooling a Chameleon

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#1 BYoesle

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Posted 19 May 2011 - 04:31 PM

In a previous thread “Imager Advice Needed v2.0" ( web page ) I decided to get a PGR Chameleon, as it had the same 1.3 megapixel count as the DMK 41, but with greater sensitivity and bit depth. It also was the least expensive of any of the models I considered. I also found a number of imagers using this camera successfully on the Sun. However, the actual chip size is quite small, requiring a custom focal reducer if I was going to obtain full-disk images with my ED100-900. I also received some input that it became a little warm and perhaps noisy. I even found a graph of the noise vs. time, and as with most CCD chips, the noise did increase about 3 fold from start up to “warmed up.”

While a little noise can be tolerated in the industrial setting for which these video cameras are intended, I don’t like taking chances, despite seeing great images taken with the camera sans any cooling. Chalk it up to being a foolish newbie imager – I decided I would attempt to engineer a cooling device using surplus and other materials as inexpensively as possible, figuring it can’t hurt, and may help. I also like to tinker with things, and the money I saved on the camera itself left room in the budget for some additional items...

I purchased the Chameleon and a Blue Fireball C-mount 1.25" adapter.

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#2 BYoesle

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Posted 19 May 2011 - 04:32 PM

Next I purchased a surplus CPU heat sink and cooling fan ($3.50 USD) and Thermal Electric Cooler (TEC -- $15 USD):

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#3 BYoesle

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Posted 19 May 2011 - 04:32 PM

Some scrap aluminum sheets were cut and shaped to make a cooling plate and housing for the camera itself. I decided not to mess with taking the camera apart for two reasons:

1. I didn’t want to void the warranty;

2. The camera itself comes with four pre-molded holes on opposite sides for mounting a tripod adapter with small screws, which would make installation of an enclosure feasible without any other issues to contend with.

I estimated the thermal electric cooler is more than capable of getting the camera colder just by the aluminum enclosure's contact with the plastic housing. The CPU heatsink is attached with thermal paste to the hot side of the TEC, and the cold plate is similarly attached to the cold side of the TEC. Small Nylon bolts were used to tighten the “TEC sandwich” for the best thermal interface. Thermal epoxy was used to attach the cold plate to the aluminum camera housing itself. Camera-side view:

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#4 BYoesle

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Posted 19 May 2011 - 04:35 PM

In my research, I became concerned that the TEC would perform too well, and possibly lead to condensation or even freezing of moisture in the camera. Thus a TEC temperature controller became necessary. Oven Industries makes the least expensive unit I could find ($55 USD), and includes pulse width modulation control, and optional temperature sensing and regulation via a thermistor ($20 USD). Fan-side view:

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#5 BYoesle

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Posted 19 May 2011 - 04:36 PM

Aluminum plates were attached to the CPU cooler for the added TEC controller electronics and switches (~ $7 USD), which control the TEC and CPU fan independently, both powered via an appropriately fused 12 volt receptacle device ($ 8 USD). I also added a scientific grade digital thermometer ($20) to keep accurate track of the cold plate temperature:

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#6 BYoesle

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Posted 19 May 2011 - 04:37 PM

In the meantime, PreciseParts fashioned an adjustable threaded sleeve to fit within the Blue Fireball, which houses the Edmund Optics 25-60 focal reduction lens. I should be able to achieve full-disk, as well as larger scale images on the detector – which are still smaller than the native 900mm focal length would allow:

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#7 BYoesle

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Posted 19 May 2011 - 04:38 PM

Chameleon with fully-retracted focal reducer:

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#8 BYoesle

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Posted 19 May 2011 - 04:38 PM

The Chameleon in its cooler with the right-angled USB 2.0 cable attached:

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#9 BYoesle

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Posted 19 May 2011 - 04:39 PM

Does it work? At ambient temp:

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#10 BYoesle

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Posted 19 May 2011 - 04:39 PM

Adjustment run – reached temp set to about 40 degrees F in less than one minute, then held steady – success!

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#11 BYoesle

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Posted 19 May 2011 - 04:40 PM

So I’m still in shakedown mode. I will now have to familiarize myself with FireCapture and the ins and outs of RegiStax, etc., but I’m excited about my new camera and looking forward to some new adventures in solar imaging. :rainbow:

#12 astrovale

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Posted 19 May 2011 - 05:09 PM

Now that is an interesting mod! I'd love to know how the performance is affected by the lower temperature of the camera. Dark noise will be reduced to a minimum and I don't really know how much that will affect the image. It shouldn't be so relevant for our kind of imaging. But if one decides to take on the moon or some of the planets, that could come handy ;)

Congratulations Bob: un gran bel lavoro!

Luca
Luca

#13 Jim Lafferty

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Posted 19 May 2011 - 06:15 PM

Bob, its guys like you that make me look bad in front of the wife--a real "do-it-your-selfer" lol. Great job on a nifty project!

Jim

#14 Naturlich

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Posted 19 May 2011 - 06:58 PM

I've been considering a similar mod for the DMK41 so your write up here is not only just great, but very helpful! Nice work Bob!

#15 bob71741

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Posted 19 May 2011 - 07:50 PM

Bob - Nice looking mod! Did you measure what the on board camera temp was before and after your mod to see what the 40°F Peltier temp relates to the on board temp ?

Bob

#16 BYoesle

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Posted 20 May 2011 - 12:19 AM

Thanks guys.

I'd love to know how the performance is affected by the lower temperature of the camera. Dark noise will be reduced to a minimum and I don't really know how much that will affect the image.

[Luca]


Luca, your comments made me curious...

Bob, I did not measure the board camera temp directly (again not wanting to take the camera apart), but apparently the FireCapture software interfaces with the PGR cameras to read some sort of internal temperature.

Here’s a cropped screen capture of the uncooled Chameleon at an ambient temperature of about 78 degrees F, with an external reading of 33.0 degrees C via the digital thermometer on the cold plate, and an internal (?) temperature showing 51.25 degrees C via FireCapture:

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#17 BYoesle

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Posted 20 May 2011 - 12:20 AM

Here’s a cropped screen capture (with identical software settings) of the cooled Chameleon at the same ambient temperature, with an external temperature reading showing the coldplate temperature of 7.3 degrees C, and an internal temperature showing 32.25 degrees C via FireCapture. Seems to have a significant effect on the noise level:

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#18 marktownley

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Posted 20 May 2011 - 01:19 AM

Bob, you are a true engineer Sir! You have my respect! What a fine project and mod for the camera! :cool:

Well, in response to Lucas question the last 2 dark noise shots say it all - at lower temperatures there is coniserably less. This can only help things, particularly prom shots with the darker background...

I've often wondered about taking darks, bias and flat shots for solar like i've done in nighttime astrophotography before. I think a job for me this weekend is going to be to get a measure of the darknoise with my DMK31...

Top thread Bob!

#19 BYoesle

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Posted 20 May 2011 - 01:44 AM

Thanks Mark!

FYI, the FireCapture software documentation indicates the “Options Panel” has “pre-processing” filters, one of which is “Stack / Darkframe.” The description states “You can also subtract a darkframe. For this cover you scope and double click the preview window (sic). You will hear a short beep which indicates the darkframe has been set and will be subtracted from the frames before stacking.”

Please let us know what you find with the DMK 31...

...I’m feeling a little overwhelmed trying to absorb all the FireCapture documentation. :foreheadslap:

#20 astrovale

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Posted 20 May 2011 - 03:09 AM

What a difference in those 2 dark frames! I did not dare asking you to perform the test, but you can always count on curiosity moving most of the people that participate here ;)

Luca

#21 robert_arnold

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Posted 20 May 2011 - 05:03 AM

Very well presented and interesting report, thanks. I am curious to know how the Chameleon performs. The temeperature / noise reduction is good but in my situation I think the seeing conditions are more of an issue, any mods to help with that would be good!
Good luck with it all
Robert

#22 solarGain

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Posted 20 May 2011 - 05:59 AM

A fine commitment to the cause Bob. Equally I am impressed with your 'ticking every box' to nail the issues that you researched. Impressive.
It is a shame that PG will not ship out of the US and Canada, it probably means also that they may not offer support overseas.
Looking forward to the drive ahead with your imaging and processing. John

#23 robert_arnold

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Posted 20 May 2011 - 09:01 AM

It is a shame that PG will not ship out of the US and Canada, it probably means also that they may not offer support overseas.

Actually they do deal with European customers via the German address, they charge $100 to ship from Canada to Europe, prices on request... $375 for the Chameleon...

Interesting camera!
Robert

#24 ASTROTRUCK

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Posted 20 May 2011 - 10:06 AM

AWESOME - next question - when are you starting your production run ??
even that reducer housing is a great idea.

#25 BYoesle

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Posted 20 May 2011 - 01:24 PM

Setting:

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