Ice on ff/fr !?

[Skipper Billy]

Just got the ED80 out after 3 months storage in a cool dry bedroom

Set it up to run some V curves ready for the incoming run of clear nights next week (!?)

After an hour or so the middle of the stars was replaced gradually by a dark circle.

After much faffing about I discovered a disk of ice crystals in the middle of the lens of the SW flattener/reducer.

Brought it inside and it cleared after half an hour - reinstalled it and it was OK for 40 mins then the same happened again.

I have wrapped a dew band round the flattener to see if that helps.

This has never happened before - any ideas! I guess it indicates unwanted moisture somewhere. The humidity just now is 87% and the temp is 0.2 degrees.

[Skipper Billy]

Could be ice on the sensor cover ???

One side of the image is more affected than the other now.

 

[Uplooker]

Hi Billy,

I can not answer you query but am very interested in the replies as I have only recently started using a refractor with a FF. I have the obligatory dewband on the objective but have been wondering whether or not I should have one on the FF

[Skipper Billy]

This is an image from Focusmax - you can clearly see a round obstruction almost completely obliterating the star

[Skipper Billy]

Two full frame images - start of session and after an hour or so - see the white stripe down the left side ???  Never had that before.

[Skipper Billy]

Just took it to bits out in the field - no obvious signs of ice or condensation on camera sensor, filters, ff/fr or objective.

Something weird at work here.

 

[Oddsocks]

That's not ice causing the artefacts in the posted image, at least, not ice outside the camera, the image is showing a CCD read defect, problems with the A to D convertor or other amplifier problem, or possibly an auto dark issue in the image capture and processing software.

Could be there has been ice build up inside the camera that has left moisture on the PCB, does your camera use a desiccant tablet or canister and have you recharged it recently?

Depending on how your system is powered it could be the extra load put on the power supply by the additional dew strap has pulled down the camera supply voltage. If the dew strap around the ff/fr is electrically leaky could be it is leaking to earth via the camera and disturbing the camera electronics. If the dew controller is not well suppressed it may be that the dew strap around the ff/fr is radiating enough noise to disturb the timing signals in the camera.

Could be the camera temperature is falling too low? what was the set temperature, look at the image fits header, the CCD temperature at acquisition should be recorded.

Happy hunting!!

 

EDIT: just noticed you have another thread running with the same question under cameras and have arrived at an answer so please ignore.

[Skipper Billy]

Thanks Oddssocks

All this  happened before I put the dew strap on the ff/fr.

The camera temp according to APT was -10 which was what I wanted and the same is recorded in the FITS header.

The desiccant tablet was baked at 190c for 90 mins  at  the start of the season (Sept).

The rig is powered by  two 170ah deep cycle batteries one for clean things that dont overlap functionally - camera, filter wheel and focuser and the other for dirty things - dew straps, mount, guide cam, etc. No common earths and as far as I know no ground loops.

Its a  mystery to me but hopefully in a strange way I hope the boys at Atik do find something conclusive  - I had serious issues with a 6" RC I bought used and  put the fact that the right hand side of the stars was missing down to my lousy collimation! I very nearly took an angle grinder to it and sent it to landfill - maybe it was the camera all along!

Thanks for taking the time to share your knowledge.

[Skipper Billy]

Quick update in case anyone has similar issues and comes across this thread.

Set up the camera indoors last night to see what happened when I took some darks. Perfect.

Buoyed up I set it up again in the observatory and ran some focus routines in Focusmax - perfect.

Tried a few trial long subs before the clouds rolled in - perfect.

The only think I changed was putting the camera in the airing cupboard for 48 hours and drying the desiccant tablet for an hour in the oven and then 24 hours on a hot radiator before re-installing in the camera.

So I dont know what the problem was but its cured (for now!!)

[Zakalwe]

That doesn't look like ice on the sensor at all to me. I've had it happen a few times and it never has a straight edge like that. Ice on the focal reducer or sensor window wouldn't be as sharply focused.

It looks like an electrical/electronic problem. Possibly a dodgy USB lead/improperly seated lead.