Flats, seen this before??

[ollypenrice]

Cor blimey, imaging with a reflector is darned hard work compared with a refractor! The ODK 14 is very fussy on flats. Too much light and reflections abound. So I'm setting up a flat run and get a perfect 2 second flat giving a gentle 20,000 ADU, just what I want. A few seconds later (literally) I start to capture the set and get this!!!

So anyone had this before? It might be dew on the camera window but it might be dew on the secondary as well. (It's suspiciously round for dew on the chip window, no? Not knowing much about reflectors I don't know.) It isn't on the filters because they all do it. Whatever it was it appeared from nowhere in seconds. Seeing the secondary directly is impossible without poking a periscope down the tube. Noooo!

EDIT, I just repeated the whole process after a gap of time and it happeed again as before, but what's odd is that the camera cooler had been running in the meantime. Initially a good flat then the reappearance of the central mystery object.

Why would starting to capture have an effect on it? The readout warms the chip slightly so I wonder if that triggers the condensation?

Olly

[JohnC64]

Thats seriously wierd. But as it was reproducable when taking a flat frame a bit later, it suggests that it is an effect close to the camera and not the secondary. So perhaps some form of condensation forming in the camera. Do the Atiks have a desicant plug? - perhaps it is "outgassing" some condensation with the slight heating from the readout?

the fact that it goes away inbetween the flats also suggests that the camera is recovering from any condensation.

Very strange indeed. Hope you find a solution

John

[ollypenrice]

Not on my Atiks, this one. They never misbehave! This is on Yves' H36. (I have yet to replace a dessicant plug in my Atik 4000s after three years of heavy use.)

You were right, it must have been chip window fog because it eventually went away.

Flats are coming in nicely now. Last night was humid by our standards so it will have been that.

Olly

[FraserClarke]

Also looks a little bit like ice forming on the chip. If the cooler is connected to the device in the middle, then I'd guess; 1) readout generates some heat 2) control system 'turns up' the cooler to compensate 3) cooling goes first to the middle of the chip and ice forms.

If it gets worse replacing/regenerating the desiccant would probably help.