Camera aimed at Sky - problems with CCD pixel burn out?

[MattVidionics 0]

Hi,

 

We have been requested to install a CCTV camera that will look at the sky (the application has not been passed on, so don't ask me why!).

In the past, if a camera was pointed directly at the sun, this would result in the CCD loosing pixels - at night, in a completely dark environment it would look like stars (dead pixels show up as white dots).

 

Can anyone offer any advice, or any filter that we can put on the lens to improve the image or safeguard it from direct sunlight (which is kind of difficult when the camera is aimed at the sky!!)

 

Thanks for any help,

 

Matt

[Soundy 1]

Make sure it has an auto-iris lens, for sure. I'd adjust the lens level as low as possible, too, so it closes as much as possible when it's bright.

 

It's really hard to know what to suggest without SOME idea of the application, as most things done to guard against sun damage will also reduce light for that application. If they want to watch the stars, for example, things become a lot more complicated, and you might be looking at some sort of timed mechanical shutter/shade. If it doesn't matter what area of the sky, it could be simply aimed away from the direction of the sun - problem solved.

[net surv 0]

Wouldn't a polarized filter work? Back in my low-budget retail days we had the same problem with a camera that was aimed at west facing exterior glass door. The sunlight would burn out the CCD in about 3-4 months. We mounted a lens from a pair of polarized sunglasses at the end of the camera lens and never had to replace it again.

[Soundy 1]

A polarizer will block reflected light when adjusted properly, which could cut sun glare off reflective objects... but it will also reduce the overall light by about two stops (1/4 the light getting through), which will darken EVERYTHING in the image.

 

Again, it's hard to say whether this would be more hindrance than help, without knowing the actual application.

[tweak'e 0]

a crude way.....why not an auto tinting lens from sunglasses ?

[Kiwi 0]

I would suggest an additional IR block filter positioned in front of the lens to supplement the one already present at the CCD. A UV block filter may or may not be helpful but is plenty cheap enough. Also, since the dynamic range you will have is significantly higher, a neutral density filter of several stops may be required.