Hi All,
I took these exposures with the Canon EOS300D (modified) two Dark Frames, one at 02 Deg. C (cooled Camera in the Fridge) the other at 27 Deg. C ambient, (a difference of 25 Deg. about what a cooled Camera runs at)ISO-800, Exp.time 10 Min. I contrast enhanced each one the same ammount, and shrank them to posing size, also JPGd them, makes one think.
Good experiment.Shows graphically how noise increases with temperature.
I have been tempted with thoughts of attaching a peltier to the back of my 20D.The major problem is access to the large control wheel and on off switch.I am now thinking along the lines of an easily removeable unit held by the tripod mount thread that maintains a cool environment for the back of the camera by forcing cool air flow from a peltier.As footprint's experiment shows even twenty degrees C drop in temperature makes a lot of difference.I think this is only necessary in summer as winter nights are cold enough.The first thing to do is to find a small fan that does not induce noticeable vibration.
Hi All,
Thanks for all the comments, BERT- Cooling the EOS300D is difficult, it wasent designed for it, two big problems- condensation and conductivity, a cold finger would be the way to go, but this means chopping up the case, I feel that a bag over the whole camera, that will allow the control leads access in which "Dry Ice" is placed could do the job, or as you suggest cold air blown via a duct into a bag surrounding the Camera- source remote from the camera, has prospects, this way fan vibration is not a problem, Etc. Etc..
By comparison my MX7C cooled camera has the Peltier plate right at the back of the CCD chip, with the hot side being heat sinked to the whole body of the camera, and the CCD chip is sealed by a glass window from the outside air to help stop condensation.
Tidalphase- Cooling the Camera in the Fridge wont harm it, as the whole of the camera contracts/expands at the same temp. the small amount of condensation quickly evaporates, but not a good idea with a Film Camera with Film in it.
Dennis,
Interesting, 6 Deg. drop in Temp. =half the noise, that I dident know, but in practice it seems that one has to cool the chip (varies from chip to chip, and CCD or CMOS) to some 20 Deg. below ambient to get useful results, but this also varies, as if you start at 30 C. you will notice a big difference in the noise level going down to 10 Deg., and of course if you start at 10 Deg. (Victorians- Tasmanians) the result will be less noticable down to -10 Deg.
Here is a quick drawing of what I was going to build.Two CPU heatsinks or similar either side of a peltier.By controlling the current through the peltier temperature can be controlled so there is no or minimal condensation.A small fan running under volted should have minimal vibration.The heat load is not high.I was going to butcher one of those small 12V fridges you can get from Jaycar.
Hi Bert,
Thats the idea, but I would have the cold side of the Pletier only in the Bag with its fan to circulate the air and not to keep bringing in and cooling outside air, An insulated duct is required also ,Fan vibration wouldent matter if the lot is not conneced to the Scope/Mount, as regards a Fan ive seen some large CPU fans that are just made for the job they take the air from the centre and push it out the sides, or use a CPU Heat sink with large fins and blow the cold air through it with the fan, or lift it through and outwards by reversing the fan direction,by the way look at www.oatleyelectronics.com they have Peltiers at a good price.
cheers....Jim
Last edited by FOOTPRINT; 26-11-2005 at 02:02 PM.
Reason: addition
Something you might consider - drill two small holes in the casing of the camera (and plug them when not using it for astro work), run thin fishtank-style clear hoses from these holes off to a pump and refrigeration unit, flush the whole thing with dry nitrogen or dry air so there is no moisture in the system and then circulate cold "air" (or nitrogen) to cool the internals of the camera to maybe 5C or so.
Something you might consider - drill two small holes in the casing of the camera (and plug them when not using it for astro work), run thin fishtank-style clear hoses from these holes off to a pump and refrigeration unit, flush the whole thing with dry nitrogen or dry air so there is no moisture in the system and then circulate cold "air" (or nitrogen) to cool the internals of the camera to maybe 5C or so.
regards, Bird
It would be safer to drill a hole in my head as it would not damage anything important.Jokes aside, even a ten to fifteen degree C drop from an ambient of 20 to 25 on a summers night would be worthwhile.My thought of using the tripod mount hole to hold the whole assembly has been done.Thanks fringe_dweller for the reference.So I will modify the design to do the same thing cool the bottom of the camera by conduction and direct cold air on to the back.More thought needed.I just wanted something that would easily attach to get a moderate amount of cooling for hot summer nights.
Howdy
I read somewhere that the Amp Glow cant be greatly reduced by cooling. I thought Amp Glow was caused by the amplifier warming that part of the image sensor but its not the case. I read that its caused by infra red photons being emitted by the transistors of the amplifier as they switch, and so they will still be emitted when cooled. The Canon D 20 turns off the amplifier during long exposures as its only needed during readout. (I wish there was a firmware hack to turn off the amp in the 300d). Note how the cooled pic shows less noise overall, but the brightest parts of the amp glow is about as bright as the warmer pic.
Scott
Hi Scott,
Thanks for that info. ex Canon, very interesting, Might put Starlight-Express Company out of business yet, they had an SONY-EXHAD Chip that had NO-Noise on a Five Min. exposure (cooled though) still quite a feat.
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