Hi all, I have an ST 8300C which I am very fond of. I bought the camera used & recently have had the problem of fogging on the chamber window or perhaps the chip itself, you may be able to tell which one from the picture below. After reading through the owners manual & consulting a couple of online forums the standard course of action seemed to be baking the desiccant bag. I tried this & the problem returned, so I replaced the desiccant with a fresh one & have done this twice now. As the problem has persisted I went back to the forums on ‘Cloudy Nights’ & my native Australian ‘Ice In Space’ for answers & apparently there was a fix from SBIG which involved a retrofit heater strip for the chamber window. Can you confirm this & are the heater strips still available? Another suggestion was that the ‘O’ ring for the chamber cover may need replacing, however I have searched Diffraction Limited’s website & cannot find either of these items listed as spare parts. I am happy to forward any necessary funds to cover parts & shipping costs. At this point I can not do any imaging at all so if you could help me I would be most grateful. Kind regards, Anthony Bailey
Our colleague @Bill may be able to assist. Am not sure if we have parts available. Bill is in the California location, so timezone is utc-7 there. Bill (at) sbig (dot) com
Thank you for your reply Colin, I have sent Bill an email a few days ago but I thought I would post my inquiry here in case there was a certain protocol to follow. No doubt he is very busy also, in any case I'm sure I'll get a reply. What are your thoughts on the heater strip remedy? Users that have installed it seem to think it's a successful fix from what I've read. Cheers, Tony
The more modern cameras have a window heater. There are compromises with everything. It might be worth looking at a camera upgrade, as a fair bit is involved to install it. An upgrade would bring the camera up to STF main board. Am not sure if this is doable for your camera. Can you provide the serial number?
Hard to tell from that image (a FITS is always better) but I think the fogging is on the external chamber window. In that case a heater is the best solution. What it does is gently heat the air in front of the window, so that dew cannot form.
S/N is 831002219 I appreciate your suggestion Colin, an upgrade may not be a viable alternative given the fact I'm located in Australia, although I'm open to the idea my main interest is finding a heating solution to remedy the fogging if that is possible. I'm fairly confident I could install the heater strip if I can acquire one but if an upgrade to an STF board is my only option I might be better off looking at a new camera depending on the cost involved. I'm pleased to having this discussion with you Colin & I thank you for your input to help me resolve this. Cheers, Tony
There may be other solutions to prevent dewing. What is in front of the camera? A filter wheel? Type of telescope?
Thanks for your reply Doug. In front of the camera is a T2 spacer for backfocus attached to a Field flatenner & the telescope is an FLT98 refractor
Hmm... it's not exposed directly to open air, so now I'm doubting that this is on the front of the chamber window. Your desiccant recharge procedure probably would not have worked. You can't bake the bag at a high enough temperature to extract the moisture without melting it. That's why we use desiccant plugs in the modern cameras - they can be baked hot enough. And whatever bag you put in there might not be good enough; we use a high performance molecular sieve desiccant. The bag you put in could be a low performance desiccant, or it could be already saturated. What we really need to know is where the moisture is. Take the camera off the scope and cool to maximum. Open the shutter and look in the front. Can you see where the moisture is? Maybe even grab a cell phone photo of it? Also wouldn't hurt to post a FITS image. Sometimes you can't tell, but sometimes you can. If there's any "fine structure" in the fogging then it has to be on the chip window.
You are correct about it not being exposed to open air Doug, whenever this has occurred a field flattener has been attached & I might add that I use 3 spacers threaded together for correct backfocus, is it possible there may be a leak there? On those occasions the fogging occurred it has been quite humid also, is there a humidity limit at which imaging is no longer viable? Tomorrow I will conduct the test you suggested to establish where the moisture is Doug, should I do this outside in my normal imaging environment? Following that I will post an image here, I have tried uploading a FITS image previously but I got an error message: file too big. I'm very grateful for the response from you guys. Many thanks, Tony
One silly thought - have you considered wrapping a dew strap e.g. a Kendrick firefly dew heater around the interface between focal reducer and camera to warm it up a bit?
FITS - if you can't upload here then please use dropbox, or use FileZilla to send it to ftp.diffractionlimited.com/incoming I'm not sure about the environmental issues, but there's no point in looking into the camera if it's not fogged! However pulling it off the telescope might fog your flatener. On that topic... are you sure the field flatener isn't the thing fogging up?
Fair comment Doug, I guess I'm assuming the fogging issue to occur under my normal humid imaging conditions (in my backyard) in which case I can check where the moisture is. I didn't consider the FF to be the problem, but I can rule that in or out when I test the rig again as discussed. I normally image with the cooling set at -10c. When the fogging has occurred previously I have just reset the cooling to -5 & then to 0 c to clear it, leaving the image train intact. In future I will investigate further by checking the chamber window & the FF to verify where the moisture is.
No problem Bill, it was basically a cut & paste of my first post at the top of this page. I'll send another to you now. Cheers, Tony
I apologize for not updating this thread sooner. I have had a discussion with Bill Lynch who has organised a heater & some correct desiccant packets to be shipped to me. When the items arrive I will install them to rule out those as contributing factors & retest the camera as outlined in post #14 and then post the results here. Obviously this might take a week or two depending on shipping & weather etc., that said, I feel confident about being able to resolve this issue now due to the excellent response from Colin, Doug & Bill. I will keep you posted. Cheers, Tony
Ok, time for an update. I received the heater strip & desiccant. Shipped very promptly, thank you Bill. At this stage I have installed the heater strip only as the desiccant packets Bill sent me were the same as those I had already installed. At this stage I am calling the heater strip a fix for the problem. Since installing the heater I have imaged for five nights in varied conditions including high humidity on the last three occasions with excellent results. No fogging/frosting or dew issues, touch wood. I can only add that I am ecstatic with the outcome & I would like to thank Colin, Doug & Bill for their support which has been exemplary. If I have any further difficulties with my SBIG instruments I will certainly return here for help. Best, Tony
