"hot" pixel issues

[Rhino172]

Anyone know what causes them?

A fair while ago I tried taking pics of the moon and got a literally just a couple, hardley even noticed them. Last night I had a quick go at some shots for the Light Graffiti thread, some I was really pleased with but some were litterally riddled with hot pixels! I'll post some examples later when I'm home.

Is it a case of dirty lens/sensor?

 

[Andy.]

You dont just mean noise do you? Low light long exposures are prone to noise.

 

[Rhino172]

You dont just mean noise do you? Low light long exposures are prone to noise.

I guess it could be, but the iso was set at 250 and exposure time was like 10 seconds so it shouldn't be.

It's not what noise would normally look like, kinda hard to explain without the picture but the background is 100% black whith lots of red and yellow pixels throughout...

 

[Ian]

Like the photo on here: http://en.wikipedia.org/wiki/Defective_pixel#Hot_pixel ?

 

[vibrio]

put lens can on and take the picture again say iso 1600 and a long exposure of 10s. turn off any noise reduction in the camera too. hot pixels will show up as red, purple, white etc on the black.

what kind of camera do you have?

 

[Rhino172]

olympus e400, i'll try that later...here's the pic..photobucket has reuced it a fair bit but you can still see them...

crop of same image..

 

[Ian]

My laptop screen is a mess, but it looks to me like dust particles in the air that are being lit up by the light?


Edit: maybe not, seems to be too many away from the light as well.

 

[Rhino172]

My laptop screen is a mess, but it looks to me like dust particles in the air that are being lit up by the light?


Edit: maybe not, seems to be too many away from the light as well.

good point about the dust...i'll try some more later, with the lens cap on and outside, see what happens...

 

[Nigel]

Some pixels have a different level of sensitivity to light than others. This only ever shows up during long exposures. Usually showing white (As shown in the image above). Most camera manufacturers allow single pixels as not being defective. If theres a cluster though they may under some circumstances repair/replace the sensor.

It's a tough one to argue with the manufacturer though, most don't want to know.

A simple test is to take a long exposure at wide aperture with the camera body cap on. Then view the image at 1:1.

 

[Rhino172]

cheers for that, I'll take a test shot, then give the camera a good clean and take another....

I'm thinking where I went the other week didn't help matters too much...dust and dirt being kicked up all over the shop...

http://www.cliosport.net/forum/showthread.php?t=407501

 

[Rhino172]

crop of bottom right corner

10s, f22, ISO100

just gave the lense and sensor a quick "blow" with my rocket blower thing and took another pic on exact same settings and the picture is exactly the same

 

[White16valver]

That's not horrendous but not great.

What camera are you using?

 

[vibrio]

hot pixels.

try the cure which works on canons it may or not work on yours.

take the lens off and switch the manual sensor cleaning system on so that the mirror lifts up. leave it like that for 2mins then switch off then on again. see if they are there.

do they go away if you turn the noise reduction

 

[Rhino172]

lol my camera doesn't have either of those functions

edit: thats a complete lie lol, just done it and taking another pic now...

 

[Rhino172]

ok so my camera seems to have a pixel mapping option, just done it and took another pic...

both the below are crops of the bottom right corner, one before the pixel mapping and one after...

before

after

much better might run it again a couple more times then try some more light graffiti now