TP: What to do about Hot Pixels

I have just carried out a 30 second exposure this evening and have found there to be 27 hot pixels, as far as I know the camera should reset these every month and so that means all these have been created in the last 26 days?

How many hot pixels should we expect before a replacement CCD?

Any details on this issue are appreciated

Mark


Edited by brettania - 03 July 2007 at 12:37

The fact there is a built in reset at the beginning of the month would suggest it's pretty common, but manageable.

harveyzone wrote: brettania wrote: keesey wrote: How many hot pixels should we expect before a replacement CCD? Never seen any info on that -- presume the problem has not yet arisen with even the 7D. How would anyone know how many hot pixels they have in total if they are mapped out every month? One would have to do a check on the last day of every month and keep a note. I am guessing that not many people do that. -- Tom.

Well, I can be a test subject, in a sense. I was looking at some birthday pictures i too just last night, and noticed 5 hot pixels, in ONE spot (reallllly annoying, beacuase they are in the middle too), in a + shape.

Do you have to do anything special to have the camera map these pixels (i mean, how would it know they are hot anyway?) Given that i am photographing a wedding this next weekend, i would like to not have shots with a big white + on em (i know, i can do a dark frame subtraction, but that will get real old after 300+ pictures...)

I am going to go power up my camera, and see if this is true. To be honest, i don't believe the camera does do that kind of mapping; i will report back either way..

You're welcome.

-

As each month goes by and the hot pixels are mapped out, eventually the sensor must run out of useable pixels.

If around 20 pixels per month was typical, then loosing 1000 or so over four years might be OK if they were well spread out. Bad news if they were grouped in the centre of the frame as in Madcap's case above.

In theory, people that fly their cameras long haul frequently should loose pixels faster because of the increased solar radiation (gamma rays is it?) which affects semiconductors (and fogs acrylic eye glass lenses).

I have never seen any info on expected sensor life and the normal failure rate calculations for semiconductors are not appropriate for individual pixels. I'd be very interested to find out.

ClevaTreva - Agreed that the normal life factors for semiconductor devices will affect CCD sensors too.
The camera sensor is a special case however - the sensor cells are working close to the theoretical limits for leakage current. (Dark current leakage in the 6MP KMD7 and KMD5 sensor is claimed to be 0.02 electrons per second - about 1 electron per minute!). Anything that causes a permanent and significant increase in this leakage current will generate a hot pixel.
Gamma rays will punch through any material and in semiconductors, may leave behind a conductive trail. In a "normal" semicoductor devices (CPU, DRAM etc.) this would not normally alter the functionality, though it is usual for electronics in satellites etc. to be "rad-hardened".
Not possible to rad-harden a photo sensor because you want light to get at it!

There is a guy in the US who recons he can judge a pilot's or astronaught's flying hours by the ammount of fogging in acrylic eye glass lenses. Each gamma particle leaves a trail in the acrylic and the cumulative effect is a visible fogging of the lens. We do get gamma rays at ground level but at far less density/frequency.

I did fly my KM5D to Italy and back with no adverse effects, but it would be really interesting if anyone who regularly flies long-haul (i.e. HIGH - not light aircraft stuff) has seen an increase in the number of hot pixels.

Hey guys, I am completely new here and this is now just my second post after posting the obligatory Hello!

I just want to say a massive thankyou to the guys in this thread that helped me get rid of the horrible white + on my CCD! I was worrying about it for the last week and just happened to find the thread on here the other day. Just tried forwarding the time on and back and lo and behold the hot pixel has gone so massive thanks for your advice!

(I have been reading the forums for a while now but never joined, had to join to say thanks tho, the advice is much appreciated)