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Old September 7th, 2006, 08:49 AM   #1
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Does heat cause bad pixels?

Hi,

I recently had to use the pixel mapping function to mask a bad pixel on my HD-100. It looks fine now, even at 18db so far....knock on wood!

I noticed it when I played back some footage I shot up in the dessert. When I arrived, my camera was in it's bag with the trunk slider pulled out to block out the sun.

Despite these precautions, my camera was quite hot when I removed it for use. The camera body is made of metal so it absorbs alot of heat. The camera worked fine but I'm wondering if this might have caused the bad pixel in my CCD?

I'm a bit paranoid now, but don't people shoot in these types of conditions all the time without any issues?

Thanks!
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Old September 7th, 2006, 02:48 PM   #2
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No - but apparently they become more agitated, and therfore visable, when heated. It also helps the cmaera mask them -

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Old September 8th, 2006, 03:44 AM   #3
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I didn't think so either. Just checking. Perhaps all that blue sky just made the pixel more visable than normal shooting conditions. Just seems strange. I've only had the camera about 6 months.
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Old September 8th, 2006, 08:39 AM   #4
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Regarding heat and blemishes. Two things:

ONE; I do find that pixel blemishes get brighter when the camera is warm. I always recommend warming the camera when doing the pixel blemish procedure. The blemish is a pixel that is generating an output signal when it should not. The blemish software closes the iris and looks for signals above the noise level in the dark. If it finds a pixel generating a signal above the noise level it says "off with its head" and removes it from all imaging tasks. You have a million pixels on each chip so missing a few will never be seen.

To be exact, the industry specs are that a camera should correct blemishes that output more than a specified signal level at 0dB. And the manufacturers do only guarantee 0dB for correctible blemishes. Having said this, we all understand we must do better than that as customers need to use gain settings so we are all more tolerant for the customer in actual use who have blemishes at gain settings.

TWO; The question of heat also relates to the development of blemishes in the first place. A CCD chip is an electronic chip first of all and it is just a bunch of chemistry. In the case of a GY-HD100 there are 1280 x 720 pixels but there is more to it than that. Don't forget the no charge domain shift register site between each two pixels on each line. SO you have 2560x720 area (give or take some) that matter. Now philosophically you can say a chip should be perfect. But also philosophically you can also say no chip is perfect. At what level are you going to look. In the substrate of chips in the circuitry pathways there are chemical impurities. If these impurities are no reactive (benign) they never matter. If they are reactive they can chemically react and grow chemically as a function of temperature, pressure, and time. So wherever an impurity is, if activated more quickly by atmospheric radiation or other source, it will grow as temperature, pressure and time. Pressure is not a factor but heat is because the "on-board" temperature (the temperature inside the chip) can be high. SO heat and time are factors.

So you build in software as we do to help the customer.

And that is a few words about heat.
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Old September 9th, 2006, 05:10 AM   #5
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Thanks Ken.

It seem what your are saying is that heat might speed up the process of a bad pixel going bad - not actually cause the malady. Or am I mis-understanding? Any tips on how to avoid overheating?

john
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Old September 9th, 2006, 01:44 PM   #6
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Right, it just helps the reaction along, it helps them grow.

I don't leave a camera in a hot car in the summer time.
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Old September 9th, 2006, 03:05 PM   #7
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Heat issues- practical problem solving

Since I'm often shooting in Arizona/ calif. desert, New Mexico and have heat issues I have adopted certain things to help control it;
1. Always shade the camera while operating- a c-stand and a flag or a small umbrella attachment mounted right on the camera top or to tripod head.
2. purchase a stick-on thermometer- a little gel like sticker available at camping supply stores usually like REI that gives temp of object it's stuck to. This lets me know that say my Varicam is at 107 degrees and is about to shut down automatically for protection.
3. Buy some gel pack freezer bags- I like the ones actually used for medical type use hot/cold as they are more durable and then I put them in a ziplock freezer bag along with some silica packets to absorb moisture and I will actually drap this over a camera that is too hot or while I'm shooting in the desert. I also use pelican cases for transport and will often put one of the above described packages inside the camera case when getting to/from location as the pelican case acts a bit like a cooler. Be sure to put extra big silica moisture absorption packets in and around the camera too. This is because we all know how electronics hate moisture and particularly spinning heads. You don't want your camera case to be freezing because then when you take it out into the 100 degree world, of course condensation can occur- this is about just keeping the camera a bit colder than the outside and that means don't run Car air conditioning at full blast either! A camera coming from a blasting cold air conditioned car into 105 degrees will eventually have problems.
4. Purchase one of those in-car electric coolers that works off of the cigarette lighter- this will allow you to keep extra gell cooler packs as back up and to at least cool down a pack that has already been used. Usually you need a real freezer to get it ready again but some of those electric coolers are pretty good when cranked up and their is the obvious advantage of no actual ice/water in this system.
5. get yourself one of those little silly personal fans that run on 2X AA batteries and try to mount it somewhere while working if there is no wind. I strap it usuallly to my umbrella attachment, aiming at the camera. Can really help if there is no wind condition to cool the camera body- You will notice many cameras have acutual cooling fins/ducting built into the body such as atop the varicam and F-900.

I've successfully worked for extended periods in 112 degree heat using these methods.
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