An issue or not?

[LewisM]

My SBIG ST-8XE develops window frost which lasts for approx. 30 minutes until it starts to clear away, totally clearing after about an hour to hour and a half. It is quite noticeable - see attached sub. The frost starts a bit higher than this, but my first subs are usually like this (after focusing etc it's started coming down). You can watch each sub having less and less visible frosting. (it is NOT vignette). This camera routinely gets to -20° C, and QUICKLY (which I am sure is a factor in the frosting).

Is this indicative of a sealing issue in the chamber, or does it need inert gas regassing? Dessicant plug need replacing or drying?

I thought I read somewhere too that these have a window heater - is this the case? I guess since it is clearing it DOES work, just slowly...

Opinions appreciated.

[Joshua Bunn]

Is this on the inside or outside of the chamber?

[LewisM]

I don't know - never disassembled it in use to check. I may run a faux-run inside and see what it does.

I suppose I could use an eyepiece dew heater to keep the front warm.

[Joshua Bunn]

if its on the outside, you could contact SBIG to see if they can supply you with an additional heater strip or two for you to stick on the outside of the chamber

[thunderchildobs]

The Desicant needs to be recharged. The details are in the ST8 manual, page 71 in my version of document.

I have to cook my desicant container about very 6 months.

Brendan

[TR]

Lewis,

Given the behaviour of the frost, ie., clearing slowly, I would recommend the following. Fire up you CCD for 20 min but don’t turn the cooler on. Let the heater heat up the CCD optical window. After 20 min, turn on the cooler. This way there is a bit of thermo mass in the window area of your camera to start with. This will slightly tip the scales for an underperforming heater strip.

This is the routine I use every time. Fire up all software and peripherals (including CCD’s) and verify that all is working. Check all wiring for possible strangulation scenarios or loose connections. I can do a polar alignment as no cooling is required for this on my rig. Soon, that 20 min is up and it’s time to turn on that cooler.
SBIG should give a procedure for recharging your Desiccant plug in the manual specific for your camera.

Terry

[LewisM]

Wife is sick today, and went to sleep at midday for a few hours... I fired up the oven at 180° and baked that darned plug for 4 hours :)

Of course, full sky cover cloud, so no testing it tonight.