Jump to content

1565608528_ReflectionNebulositybanner.jpg.5b3647faf258fca0cd9c62694d6e7b71.jpg

Cooled (or not) DSLR - Real life comparison


Recommended Posts

Out of boredom (mount out of commission for a while), curiosity (I like to make my own opinion), necessity (I don't have uber money) I endeavoured to DIY a cooled box for modded canon DSLR (I sacrificied a 450D) .  With a few specific things that would decide if it was a success or a waste of time; namely, I wanted to be able to

  • set a specific temperature for the sensor, so as to be able to calibrate my darks (that is one of the most often quoted argument AGAINST cooling boxes) 
  • cool the sensor 10/12C under functional temperature (as the thermal noise is reduced by half for every 5C of cooling)
  • keep under 1.5kg
  • be able to SEE the difference on my lights without pixel peeping. 

I am not going to get into the build itself and all the tests I have conducted for the past 2 or 3 weeks, because it would be long and boring, but simply jump to the final result. 
This are two unprocessed, 100% crops. Canon 450D modded on SW130PDS/CG5GT, guided, 600s, ISO800, taken about 1 hour apart.  One is not cooled (ambient temp: 20C, sensor temp: 28C) one is cooled (ambient temp:18C, sensor temp: 8C) 
No points for figuring out which is which. 

It was not a total success because there are a few details that did not pan out as planned (and because I proved to be an imbecile who did not consider that the ambient temp would fall later during the night!) and therefore, more dev is left to undertake BUT I think it is fair to say that for an investment under £150 including the camera, the work in my opinion is totally worth it. 

One of the things I have come to realise during the design/build is that, while everyone seems to consider the temperature of the sensor vs ambient temperature, this is actually irrelevant; what counts is the temperature the sensor reaches when cooled vs when uncooled, regardless of ambient temperature, because uncooled the sensor will get much warmer than the air (typically for this specific dslr, 10C).  And this difference does not have to be massive to see a real improvement in fact, other comparisons and tests I have made convinced me that cooling by just 6 to 10C make an absolutely massive difference in the "cleanliness" or level of detail of the light frames.  In this case, uncooled : a very noisy image purely due to thermal noise and the infamous ""canon banding" is very visible; cooled by 20C, the light frame is virtually noise free with a very smooth background. 

I hope this will inspire others :) 


cooledOrNot.thumb.jpeg.3549b1c82d0f18db0365fe89951c3e4c.jpeg

  • Like 3
Link to comment
Share on other sites

Big difference. Some attach the peltier element to the camera itself (with or without fan - AstroBiscuit did this on one of his hilarious videos), while others make an insulated box, with element, vents and fan (Gary Honis has a couple of really good descriptions out). What's your approach? Image mostly in cold weather, but being a tinkerer, this is tempting!

Link to comment
Share on other sites

It's a cooled box "with a twist". Here it is

1779316193_WhatsAppImage2022-08-26at7_38.48PM(3).thumb.jpeg.a9c83c61ad12978b02b593f7d724427a.jpeg

 

Red : current temperature of the heat shield, blue, target temperature, 22.2C = cold heat sink temperature and 23.6C = ambient air temperature. With these and looking at the current local dew point it is possible to set the ideal target temperature, as cold as possible while avoiding condensation/fogging/frost. And because it can be set, it is straight forward to make libraries of darks that are perfectly calibrated. The excellent freeware ExifLog also helps a lot to check temps variations over a series (and was critical during tests to put the shield probe EXACTLY at the right place so that the set temperature = sensor temperature) 

 

238270256_WhatsAppImage2022-08-26at7_38.48PM(2).thumb.jpeg.6b516d3ab6a83f24c34a78db522fa0ea.jpeg

 



And here it is on  the telescope
 

220108889_WhatsAppImage2022-08-25at6_08.40PM(1).thumb.jpeg.e102158b3e48f4e05346c00f6251e26b.jpeg

The 4 cables coming out are : cold cell PSU, DSLR usb connexion, DSLR PSU, ambient air temperature probe

1345543323_WhatsAppImage2022-08-26at7_38_49PM.thumb.jpeg.8ccf80f542dac6c0e57286c10fe77684.jpeg

The twist is that the box itself is separated in 2 compartments, the cooled box itself and a separate zone where the electronics are (because along with the wiring they also give off quite some heat) The partition is made of wood because it is easy to work and is a very good thermal insulant.  Beside, it decreases the volume of the cooled zone as much as possible. 

  

1303830720_WhatsAppImage2022-08-26at7_38.48PM(1).thumb.jpeg.e261a79c161e7600ec947f98d6cb6652.jpeg

You can also see in the middle of the back of the box (flipped over) the temp probe of the thermostat, placed so that it presses against the heat shield of the sensor. The bubble padding adds insulation and acts as a spring to ensure intimate contact. 

The cable that goes inside the cold heat sink is another temp probe that measures the temp of the cold side of the peltier cell (to judge how fast it is cooling / warming up and make sure it is not far below 0C) 

976530551_WhatsAppImage2022-08-26at7_38_48PM.thumb.jpeg.29feea99bfe10ac082ee4534e3476c50.jpeg

The back of the camera is gone permanently, the fan on the cold heatsink ensure the air circulates straignt within the electronics. Under the heat sink where the USB is connected, and under the cell PSU cable I pack silica gel (2x 20G). As the box is pretty much air tight it prevent condensation very well. 

The camera in its original state heats the sensor up to Ambient +10C. In this config the sensor can be Ambient - 9C. That's -19C and is actually too much as I learned the hard way yesterday (frost on the outer side of the field flattener when the air temp fell to 10C and the cold cell went down to -8.5C, sensor just above freezing) The thermostat allows to maintain a safety temperature without fogging or frost (sensor around 8C) as the field flattener is in effect wormed up by the metal focuser. So the trick will be to set the proper temperature which is 1) above freezing 2) just under the dew point (the sensore being 1 or 2 degrees above the set temperature) Yesterday I f**** up because I just forgot that the temp would drop at night... and I left the thermostat to -50C, forcing the cell full blast for 3 hours.

The current PSU is 12V3A but the peltier is rated for 6A so another psu is on its way. Also, I will ad 8mm neopren foam on the front side to limit heat exchange (the insulation is thiner there to ensure proper square contact of the ring against the front). It's not about getting cold faster but about preventing fast warming when the peltier cuts off at the target temperature: this will allow a more constant temp. It seems that with this specific sensor my ideal target temperature is around 6-8C which should be safe in most situations, except maybe in heatwaves where I'll need 10-15C; but even at 15C, the image is so much cleaner than uncooled that I can absolutely live with whatever little noise is left.  

  • Like 6
Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue. By using this site, you agree to our Terms of Use.