1100D cold finger sensor cooling with TEC and water cooling

[Gina]

Excellent Gina. Brilliant result. Definitely need the enclosure and tube connection to the scope to control condensation. I don't think the same is possible with my conventional lens set up.

Thank you I intend to look into the possibility of using this system with a lens for wide field use. I think it should be possible. It will a little while before I do this though because I want to look into computer control for set point temperature control next.

The novice that I am when it comes to electronics, I have put off making a dew heater for the face of the Astrodon filter and would appreciate your thoughts, guidance as to design that you may be willing to impart.

I presume you mean a variable power dew heater using power MOSFETs like I am for the TEC control. In fact the same circuit would be quite suitable for a dew heater.

[rcheshire]

Precisely. Although I will use an Arduino for PWM, driving a logic level MOSFET (same as my DSLR cooling mod), about 75mm of Nichrome wire to fit around the perimeter of the filter face and just enough power to keep the filter temperature 2C above dewpoint. At -10C and a dew point of 10C the element would need to be capable of a heating differential of 22C. A series power limiting resistor would prevent overheating. That's the basic idea anyway.

Could be run of the same MOSFET as the cooling circuit, programming a relationship between set point temperature and a nominated dew point value to automatically regulate power to the dew heater. That's the easy part. Interested in your thoughts.

[Gina]

Precisely. Although I will use an Arduino for PWM, driving a logic level MOSFET (same as my DSLR cooling mod), about 75mm of Nichrome wire to fit around the perimeter of the filter face and just enough power to keep the filter temperature 2C above dewpoint. At -10C and a dew point of 10C the element would need to be capable of a heating differential of 22C. A series power limiting resistor would prevent overheating. That's the basic idea anyway.

Could be run of the same MOSFET as the cooling circuit, programming a relationship between set point temperature and a nominated dew point value to automatically regulate power to the dew heater. That's the easy part. Interested in your thoughts.

Sounds reasonable to me but I have no knowledge of Arduinos. I guess it is possible to calculate how much heat you would require to prevent dewing - I might have been able to do that when I was younger but nowadays that's far too much for my poor old brain

[Gina]

I can now report on my cooling system performance in real life. Success! -14C and no condensation or interference in the images with 5 minute subs at ISO1600. :hello2:

A lot of faffing about last night trying to find where I was in the sky and trying to find something to image. Found a nice bright star to focus on using Bahtinov mask. I think after 2 months of useless night skies I was rather rusty but eventually I found the Iris Nebula which appeared near the bottom of the frame. I would have liked it nearer the centre but after all the effort finding it I didn't want to risk slewing the wrong way and losing it. Plus I had already lost a lot of time finding it. Then I got PHD up and running - seemed to take ages to calibrate but it always does That worked well for about an hour then started losing the star. During this time I took about 10 x 300s (5 minute) subs at ISO 1600. Guiding and focus seemed perfect for that time but the proof of the pudding will be in the results.

I checked the sky and it still seemed clear so I decided to try another target and after a few tries found the Veil Nebula - a nice big though faint object. I think there might have been thin high cloud or mist as I had enormous difficulty getting PHD to find a star. Eventually I had to give up at around 2am as the cloud had come over. The dew was very heavy last night too and that might have contributed to the difficulties. Anyway, I did see the Veil Nebula in the long subs but the images won't be much good due to star trailing .

[Stu]

Fantastic news Gina.

I've found reading this thread exhausting enough so goodness knows how you must feel!

It really is a triumph of intellect and sheer energy, enthusiasm and hard work over adversity to get it sorted so you must be well chuffed :D:D

Looking forward to the images rolling in as soon as the weather clears and the skies get a bit darker....

Enjoy.

Stu

[Gina]

Fantastic news Gina.

Thank you

I've found reading this thread exhausting enough so goodness knows how you must feel!

Shattered

It really is a triumph of intellect and sheer energy, enthusiasm and hard work over adversity to get it sorted so you must be well chuffed :D:D

Yes, I'm pretty pleased, I must say Got there in the end

Looking forward to the images rolling in as soon as the weather clears and the skies get a bit darker....

Enjoy.

Stu

Got some last night - first partly clear night for 2 months. Only trouble is my DSS Beta version that handles the new Digic 4 CR2 files has disappeared from my Win 7 box Very strange! Will have to download it again and unpack it.

[Stu]

Just heard a wooshing sound as that last past went right over my head

Stu

[Gina]

[Gina]

Good imaging session last night. Camera working fine - producing an EXIF T of -15C. Made full use of the 2 hours of adequate darkness to capture the Veil Nebula (see "imaging - Deep Sky" forum for details). Don't think we'll get another clear night for a while now

Need to clean the sensor which has collected some dust etc. - not too surprising considering how often the camera has been in and out of the box. At least I can access the sensor for cleaning without taking the camera out of the box. Just a matter of unscrewing the focal reducer and removing the clip filter.

[Gina]

Took camera off and cleaned sensor - much better now though still a few faint dust bunnies showing in some new flats I've taken.

Only trouble is... something seems to have gone wrong with the cooling so I'll do some testing with ammeters but suspect the camera will have to come off again for examination.

[Gina]

Here's one of the new flats.

[Gina]

Found the problem with the cooling. The 12v Peltier TEC has gone open circuit. Don't have another 50W 12v TEC ATM but have a couple of 136W 12v ones so I'm putting one of those in. I know it won't be as good but should give me some cooling while I wait for a replacement 50W.

[Gina]

Cooling working again but nowhere as efficiently as before - I'll be lucky to get down to freeziing Unfortunately the TECs on eBay are 6-8 working days delivery even from a UK supplier. I've ordered a replacement for the 50W TEC plus a spare and a spare for the 5V 20W.

Oh well, the weather remains bad anyway - if that's any consolation. I do have my no.2 1100D set up for wide field with nice fast lenses, so that's something

[Gina]

Best EXIF T so far is +4C and that's with short exposures so my -15C subs will be out until I get a replacement TEC Probably the week after next - beginning of July. Looks like we might get some clear skies tonight too, in which case I'll try out my wide field camera. Haven't done the filter removal mod yet though. Was going to do that today but spent the time fixing (?) the cooling on the other.