pointing update failures

yes, but do I need a return authorization, instructions etc.?

 

Got it and will have it shipped in the AM. But we want to share some concerns and questions we have related to making sure that any condition that contributed to this is addressed while you have the unit and that we all have a realistic understanding of why this happened and what we must do to avoid this in the future.


Regarding the first issue, we are concerned that the chamber environment was somehow compromised. We base that on two things. One is the residue of a presumably soluble substance on the chip. The other is the chamber should have been dry and the desiccant freshened when the camera was in for service last spring, yet enough moisture, even apparently liquid water, given the residue, was present only a few months later.


Your manual recommends a routine refreshing of the desiccant each year. Even in a humid environment, it says six to nine months unless it is opened frequently. The camera was shipped back to us in early May and not opened prior to the discovery of the subject condition. By Sept. 7th, just four months post service, it is now evident there was already a residue developing on the chip, implying a significant moisture problem (liquid water?) existed well before Sept. 7th. A three-month desiccant recharging cycle would have been required to prevent this. Such a schedule is not suggested in the manual. We are not aware of any visual frosting event prior to the one that gives rise to this discussion.


It seems to us that the residue in question had to come from inside the unit, as water vapor does not contain dissolved solids. Given the fact that the presence of moisture in the chamber is anticipated and the sensitivity of cleaning this chip, I should think that there should be nothing soluble in the chamber that could leave a residue. What is the residue? Where did it come from? Naturally, these are among the questions we have.

As noted, several of us have owned SBIG cameras. I used an ST-10 for five or six years, running it every clear dark moment on photometry patrols. About once a year or so, some early evening images would show frost. It was a small nuisance, it was not a big concern, and there was never a visible residue left on the chip. This very observatory used an ST-9 for several years as well, with similar experience. Never has a solid residue been seen on the chips of these cameras.


The only clue we have had that, in retrospect, might relate to this problem is a few sporadic reports of failure to plate solve starting about a month ago, mostly involving pointing updates. Suspecting the small FOV was a factor, we recently installed the ATLAS star catalog. However, to our current knowledge, images were seen as visually acceptable until a few days ago. Only when the subject flat failed to plate solve, leading to a close examination, did we see evidence of frost. We are polling our users to see if anyone saw something they did not share earlier. But up to the time of discovery, only one user complained about a poor image, and that involved some banding in a stretched image that didn’t match the pattern we saw on the flat, giving rise to this discussion.


Barring a significant compromise in the seals of the camera or the desiccant cartridge gasket, or a failure to properly service it prior to shipping it back to us, we are at a loss to explain the situation. We would, therefore, ask that the sealing be checked, if possible, prior to disassembly and that some effort be made to determine the nature of the contaminant and its source. With a covered chip, this would not be such a big issue. With this chip it is a serious concern.


I feel compelled to say that this camera has been a big disappointment. Aside from the prior defect with the temperature gauge, the bearing problem in the filter wheel, and this instance, the expense and trouble of shipping out of the country for service, and the complexity of the operation and calibration process required for scientific imaging in a robotic multi-user system have also presented unanticipated challenges. The camera better lends itself to an individual user. If this degree of uncertainty in the development of moisture inside the camera is inherent in the design, especially given the vulnerability of the chip, it poses a serious challenge for us to use it safely and raises a question about the practicality of incorporating this kind of chip in a camera body that is so susceptible to accumulating moisture.


Thanks again for your help, and we look forward to your honest assessment of the source of this problem and a practical and equitable path forward.


Bruce McMath

 

We received this camera today and look forward to putting it to work. We assume that no damage to the chip was evident post-cleaning. But please share what conclusions were reached about the nature and source of the contaminant on the chip and how moisture developed so quickly.


We are considering a program of recharging the desiccant in early May and late September, but given the exposed nature of the chip, worry this may not be sufficient to address the risk depending on what your findings were.


Part of the problem may be the robotic life this camera lives. An individual user who engages the camera on individual imaging projects would readily spot the earliest sign of moisture. In our case, the camera comes on as part of the start-up process, and frost on the chip may sublimate before any images are made. If that leaves a residue, we will soon be back with a stained chip.


Thanks for your attention


Bruce