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Long Exposure Noise Phenomenon


tigerminx 10 237 South Africa
20 Nov 2006 4:47PM
I had the opportunity this weekend to try out long exposures with the 30D, after a 10 minute exposure I noticed a really horrible looking blue gradient on the bottom edge of the frame. Thinking it was the lens I tried the 50mm F1.4 with the lens cap on and an exposure of 135 Secs @ F3.5 I noticed the same phenomenon. I took the camera back to the reseller today, and they had no clue. (The camera has since been sent back to Canon in Johannesburg.) Was wondering if anyone could shed some light on my dilemma?

I have attached a resized test image here:

Resized Image

And a 100% crop of the image here:

100% Crop

Exposure was 120 Secs @ F3.5 using an ISO of 1600. (Seems to happen on all ISO's)

I've heard of heat induced noise or "amplifier glow", but surely not after 120 secs and so severe?

Thanks in advance.
Bruce.

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dougv e2
10 8.4k 3 England
20 Nov 2006 4:57PM
Was the camera hot Bruce?

Astronomical cameras are cooled to reduce noise.
However, this looks like it may be a faulty sensor.
It certainly isn't pretty.

Doug ;o)
tigerminx 10 237 South Africa
20 Nov 2006 5:00PM
Camera was out in the cold Doug, I was wearing nearly 3 layers of clothing.

Strange thing is regular exposures (1 - 30 secs) are not affected. If the sensor is faulty, what is Canon's policy? The camera is still under guarantee.

Bruce.
cambirder 10 7.2k England
20 Nov 2006 6:04PM
I would not have thought that long exposures and high ISO's go that well together, I'm not surprised you got some interesting results.
tigerminx 10 237 South Africa
20 Nov 2006 6:07PM
If you read my post above I clearly state that it happens on all ISO's.
cambirder 10 7.2k England
20 Nov 2006 6:29PM
Sorry tiger I missed that, just tried it on my 1D Mk2, iso 1600 130sec, with noise reduction on and off. Some hot pixcels with NR off but nothing like you are getting, does sound like a dodgy sensor you have there.
elikag 10 749
21 Nov 2006 11:57AM
This happens on the bottom of the image, that means the top of the sensor.

Have you used the included rubber-thingy to block any stray light from entering the viewfinder? It seems like you get some stray light coming trough the viewfinder and fogging your images.

The blue tint may be due to some optical merits of the pentaprism.

HTH,
Ilia Kagan.
tigerminx 10 237 South Africa
21 Nov 2006 12:43PM
Hi, I used the eyepiece cover that's on the neck strap. My previous camera was a 300D. I managed to do a 40 minute exposure without the eyepiece cover, and didn't have the problem mentioned above.

Bruce.
Tandberg 11 1.2k 2 England
21 Nov 2006 1:41PM
I do 10 minute exposures all the time

Try 10 minutes at 5.6 and a low iso!!

I use iso 50 on the 5d and no noise reduction on..

Make sure the camera is adjusted to the cold and you should have no problem..

Have a quick look at my night stuff and see for yourself
dave
mattw 10 5.2k 10 United Kingdom
21 Nov 2006 1:48PM
Very strange Bruce - sending back to Canon sounds about right.

Mattw
tigerminx 10 237 South Africa
5 Dec 2006 6:47AM
All Canon's Sensor Calibration did was waste a couple days. 2 weeks now without the camera, and they have finally decided to replace the sensor? Should I be worried?
strawman 10 22.0k 16 United Kingdom
5 Dec 2006 10:09AM

Quote:Should I be worried?


Not realy, because if they change it correctly your camera will either be fixed or they will have to get you another. These things are normaly done at sub assembly level so the risk of change is probably low. There will be new ones where sensors will be changes as part of normal manufacturing rectification. Also because they know of your concern they should test it to make certain it is ok.

Mind you 10 min, that is a very long exposure, it could be long enough for in-camera thermal effects to show up.
tigerminx 10 237 South Africa
5 Dec 2006 11:24AM
Thanks for the reassurance. I suppose It's either gonna work, or they will have to replace. It's just knowing that a 5 month old camera, has already had open heart surgery Smile

Surely 10 minutes is not that long in terms of Digital SLR exposures? I remember on my 300D I managed an exposure of about 40 minutes. A bit of noise, but nothing near the likes of the image I posted above.

Thanks again.
Bruce.

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