How do i stop ccd Dewing

[ribuck]

Hi all,

I'm starting to ge really fed up with Astronomy, no matter what i do, as soon as i solve 1 problem it's replaced with another, so i'm in desperate need of help before i decide to sell up fro good.

I have a starlight Xpress camera, and tonight is a rare occasion where i got a clear night, and once again my starlight xpress MX916 ccd keeps on fogging up and stopping me from imaging.

The dewing takes place in the same spot every time, a perfect circular spot in the center of the ccd glass on the outside.

I've cleared the dew away 3 times tonight only for it to come back andi'm fed up.

Is there some fundemantal thing i'm missing like dont try imaging if it's slightly cold ?

Sorry to rant like this, just getting tired of everything being a uphill struggle instead of enjoying the hobby.

Rich.

[George]

Small dew strip round the focuser tube usally does the trick.

[narrowbandpaul]

i believe its moisture condensing on the cold glass. we had the same issue with the h9 but one clean fixed it.

the ccd chamber should be purged with something like argon.

[ribuck]

Hi George,

If i put a dew heater around the Focuser tube will it not interfere with me focusing or doe you mean a dew heater attached to the outside housing of the draw tube ?

The trouble i have is that i have such little inward focus i have my ccd connected to my filterwheel with a M42 adapter, then the filter wheel connects directly to the draw tube 2" adapter without any nose piece. So i dont really have anywhere i can put a heater.

Does anyone else have any idea's ?

Paul, how would i purge the chamber as it's sealed, i presume this is something Starlight would need to do ?

One option i thought about is relating to diving, where you can buy some special anti-mist sollution for the inside of your diving mask, i wonder if this would also work on the ccd glass ?

[Psychobilly]

in its most minimal form of dew heater you can use a length of resistance wire insulated with heatshrink...which helpfully self shrinks when you overdrive the wire...

Billy...

[Ford Prefect]

Try heating the camera with any filter attached on the radiator prior to taking it outside. It seems to work for my qhy8

Cheers Jon

[CELESCOPE]

Used to happen with me all the time with my Atik ccd 16hr.when i imaged outside , got really fed up , threw a yellow dusty over the ccd in anger , found it cured the problem ,never had the dew again, simple cheap ,

Now its under the DOME so no problems there .

so try the YDT.

Rog

[roundycat]

I often have this problem with my Atik guide camera. It only seems to be a problem when the scope, adaptors and camera have been taken apart for any reason and then re-assembled out in the cold. Try putting it all together in a warm room with all the bits up to temperature and then take it out and use it but don't open it up in the cold.

Dennis

[ribuck]

Hi All,

My ccd normally sits attached to the filter wheel in my DIY Obs outside. Whilst my obs is not perfect and does have some moisture ingress, the scope and ccd is always kept under an expensive scope coat, which waterprrof lining etc. Forgot the name of the coat, something 365 if i recall.

The dewing always just seems to take place, after about 10-15 mins of operation.

Could i put a dew heater on the end of the ccd housing, or would this cause unwanted effects.

With regards to assebling the filterwheel, ccd etc at room temprature, I have already done this when i was sorting issues with my filterwheel. The camera and ccd had been indoors in bits for about a week before it was reassembled and taken outside.

Rich.

[ribuck]

A colleage suggested i buy some moisture traps from places like Wilkinson and place in the observatory to see if it helps.

[jkty5597]

Hi Rog:

What is yellow dusty?  Is it a bonnet???  Im also using an ATIK 16HR and having  dewing problem as well on the front glass of the ccd.  I also try using a dew heater strip strapped on the camera barrel and it seems also help lessen the dew issue.

My main concerns also is that I use the 16hr ccd camera on the Canon EF100-400mm IS L lens thus I cant use my filter wheel or it will not reach focus   Thus I need to remove the ccd camera off the lens for me to replace the LRGB filter individually thus also have more susceptibility of dewing the front glass of the ccd camera everytime I replace the needed filter.  Any extra remedy I can do to lessen the dewing problem?

JAMES KEVIN TY

[jkty5597]

I often have this problem with my Atik guide camera. It only seems to be a problem when the scope, adaptors and camera have been taken apart for any reason and then re-assembled out in the cold. Try putting it all together in a warm room with all the bits up to temperature and then take it out and use it but don't open it up in the cold.

Dennis

Dear Dennis:

I often have to open the 16hr camera up to replace a needed LRGB filter since i cant use a filter wheel on the 100-400mm IS L lens   Think if I open up the camera inside a changing bag covered on the ccd camera will help lessen dewing?

JAMES KEVIN TY

[ollypenrice]

CCD cameras should have dessicants and, if highly cooled, heated chip windows. Atik know this and, I'm sorry to say, Starlight Xpress don't. I use two full frame Aitks and one full frame SX. I lose several nights a year with the SX and none with the Atiks. Sorry to be blunt but that's about it.

Olly

Edit; to make matters worse, the Atiks (which don't mist up) out cool the SX by typically  4 or 5 degrees.)

[RobH]

Hello James Kevin. I'm afraid you won't get an answer from Rog or Dennis as they no longer frequent SGL.

I have owned a 16hr since 2008 and have never had a dewing problem with it . If you have to go through the process you describe to change filters, then a quick blast with a hair dryer will do the trick (12v hair dryers are much safer in damp conditions.....you want to image the stars, not end up being up with them!). Generally though, I'd wrap a dew band around the camera nosepiece.

[smithygar]

Hi,

  I use a H9, & SX filterwheel on a 200mm reflector. I had the problems you encountered, with the outside of the CCD window dewing (damned annoying isn't it!!!). The open tube design of a reflector is always going to be susceptible to this problem, not being a "sealed" system. A mate of mine made me a small ring of resistors covered in shrink wrap. This fits inside the front of the camera, up against the glass. The wires then pass through the filterwheel & out the side of it through a small gap where one of the electrical connections is (it's really thin wire). I put a small flocked plastic tube inside the camera/filterwheel junction for the wires to tuck behind & keep them out of the light path.

   Since I've done this mod I've never once had any dewing problems & would recommend it as a cure to anyone.

[cfpendock]

As Olly says, some of the Atiks have heated windows which does seem to prevent dewing.  However, I have found that my Atik 4000 does sometimes deposit ice on the actual chip (not the window, which stays clean), especially when cooling down (normally operating around -20).  The ice does usually disappear within an hour or so, and I believe is caused by moisture within the camera.  This is a possibly a consequence of the season and of keeping the camera outside.  

I have written to Atik about this problem, but unfortunately it seems there is no obvious way to replace desiccant on this model, so I suppose I should keep the camera in a closed box with some desiccant.  The problem with this is that it means taking the camera off the scope, and hence losing the ability to take flats the next day. 

Chris

[ollypenrice]

As Olly says, some of the Atiks have heated windows which does seem to prevent dewing.  However, I have found that my Atik 4000 does sometimes deposit ice on the actual chip (not the window, which stays clean), especially when cooling down (normally operating around -20).  The ice does usually disappear within an hour or so, and I believe is caused by moisture within the camera.  This is a possibly a consequence of the season and of keeping the camera outside.  

I have written to Atik about this problem, but unfortunately it seems there is no obvious way to replace desiccant on this model, so I suppose I should keep the camera in a closed box with some desiccant.  The problem with this is that it means taking the camera off the scope, and hence losing the ability to take flats the next day. 

Chris

No, you don't need to lose your flats if you're reasonably careful. Mark the position of the camera using Tippex or sticky paper and just be quick and careful when removing it to get plastic bags over scope and camera. I think you'll find that your flats will still work later on.

Olly

[cfpendock]

Thanks, Olly.  I'll try that, I was worried that I wouldn't be able to put the camera back sufficiently accurately for any dust bugs.  Certainly it should be sufficiently accurate for vignetting which for me is generally the most important reason to use flats.

Chris

[x6gas]

Not that it helps you, but I have never had a problem with any of my Atiks either...

I did get ice on the edge of the chip of my 383L+ a couple of times, but changing the desiccant (which you can 'recharge' by heating in an oven) solved that.

[RobH]

Thanks, Olly.  I'll try that, I was worried that I wouldn't be able to put the camera back sufficiently accurately for any dust bugs.  Certainly it should be sufficiently accurate for vignetting which for me is generally the most important reason to use flats.

Chris

You won't be accurate enough for any dust bunnies, but if you have clean filters that'll be okay. It will, using Olly's method, be good enough for vignetting though.

[Uranium235]

Not that it helps you, but I have never had a problem with any of my Atiks either...

I did get ice on the edge of the chip of my 383L+ a couple of times, but changing the desiccant (which you can 'recharge' by heating in an oven) solved that.

Have to agree - change the dessicant - even if the camera is new out of the box. My 383 frosted up from new, but that went away after I changed the dessicant (you get a spare pack in the box). When not in use, I also bag the camera and FW with a zipper bag that contains a large silica gel sachet - just to keep it extra-dry.