Horrendous Halo

[PhotoGav]

No, this isn't a previously undiscovered planetary nebula... Occassionally I get a huge halo on my images at the start of an imaging session. It disappears over about 30 minutes or so. It must be on the chip or at least the window over the chip as it is the same for all filters. Is this normal? Is my CCD going to suffer as a result of this? I am guessing it is condensation of some description? I'm interested to hear if anyone else has seen this. I can't be the only one!

 

[whipdry]

Hi Gav,

Your not alone, been getting the same on my Atik One 9.

 

Peter

[PhotoGav]

Peter, that's good to hear and not good to hear, if you know what I mean! Thank you for the reassurance.

[Thalestris24]

Looks like gravitational lensing to me  Must be dark matter...

Louise

[Davey-T]

Just had it earlier and it was dew inside the Star 71 took it indoors for ten minutes and it cleared, still clear now, pity the skies not 

Dave

[gnomus]

I've had the same thing here in the moist-Midlands.  I am certain that it is condensation on the front glass of the CCD, forming as the camera cools.  Mine clears up within minutes.  I am generally messing around with my framing and autofocus routines at the start of the session so I am taking multiple short (10-25 second exposures) repeatedly during this time.  I see the halo gradually disappearing until it vanishes altogether after a few minutes.  I assume that the heat generated by my multiple exposures is clearing the condensation.  Since I am waiting for the scope to cool down anyway, I don't feel I'm losing any imaging time.  My suggestion, therefore, is to run several 'frame and focus' exposures until you see it clearing.

[swag72]

Yep happens out here in Spain too   It seems to happen when the obs is first opened ..... I let the scopes cool for at least an hour anyway and by that time it's all gone

[PhotoGav]

Thank you for your replies everyone - I'm glad to hear that I am not alone. It does appear to be when it has been particularly damp, so must be condensation. Thankfully it disappears fairly quickly. Unlike the clouds...........

[ollypenrice]

I have seen it too, though never on the pair of Atik 11000s we have here. These fine creatures have chip window heating, which I run by default since I'm on mains power. Other cameras do it routinely. What you can do, if you like, is give the camera a bit of heating prior to use. When it has been damp for a while I use the hair drier on the SXVH36 on and off before darkness fully falls and this anticipates the problem and prevents it from happening. The big window of this full frame camera does not clear quickly once dew has formed, so pre-emptive action is important.

Olly

[reddoss]

Definitely moisture, I get occasionally.

[martin_h]

I get it as well, I usually give it a blast with my £5 Tesco hairdryer. ?

[PhotoGav]

I thought I would give a quick update on the condensation halo problem... I changed my dehumidifier from a compressor type to a dessicant type and I have not seen the halo problem reoccur so far. It has been pretty damp just recently and the kit hasn't been used for a few days on a couple of occasions, but still no halo when I start everything up. So, I conclude that the old dehumidifier was pants!

 

[gnomus]

I have found that if I start up the cameras (without cooling them) at the same time as I open the roof to let the scope cool, I rarely have issues.  It is when I rush out to get everything started that I occasionally get this.

[Davey-T]

I had it tonight but mine is outside under a cover, the humidity has been at nearly 100% for days so not surprising, had to give it a blast with the hairdryer and then leave it for 10min to clear.

Then I changed to O111 filter and forgot to refocus and wasted a 30min sub, then I changed to autosave and forgot to switch off subframe so wasted another 30min sub. 

And I hadn't even had a drink, making up for it now 

Dave

[steppenwolf]

6 hours ago, PhotoGav said:

I changed my dehumidifier from a compressor type to a dessicant type

A compressor type will only work at temperatures above 10 or so degrees which is why I am always banging on about getting a desiccant type for an observatory. A compressor type simply won't wok in the winter months. There is one caveat to this, some compressor types have a heating cycle which allows them to operate at slightly lower ambient temperatures.

[PhotoGav]

3 hours ago, steppenwolf said:

A compressor type will only work at temperatures above 10 or so degrees which is why I am always banging on about getting a desiccant type for an observatory. A compressor type simply won't wok in the winter months. There is one caveat to this, some compressor types have a heating cycle which allows them to operate at slightly lower ambient temperatures.

Unfortunately I have found this out the hard way!

 

7 hours ago, gnomus said:

I have found that if I start up the cameras (without cooling them) at the same time as I open the roof to let the scope cool, I rarely have issues.  It is when I rush out to get everything started that I occasionally get this.

Sounds like like a good approach - hopefully we will have some clear nights to put it all to the test.

 

6 hours ago, Davey-T said:

I had it tonight but mine is outside under a cover, the humidity has been at nearly 100% for days so not surprising, had to give it a blast with the hairdryer and then leave it for 10min to clear.

Then I changed to O111 filter and forgot to refocus and wasted a 30min sub, then I changed to autosave and forgot to switch off subframe so wasted another 30min sub. 

And I hadn't even had a drink, making up for it now 

Dave

All I can say is 'Aaaaaarrrrrrgggggghhhhhh!  '

 

 

[gnomus]

14 minutes ago, PhotoGav said:

...

Sounds like like a good approach - hopefully we will have some clear nights to put it all to the test.

 

Now you're just being silly.