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Author Topic: 7D- Hot Pixels and Noisy Photos  (Read 2255 times)

murray09

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7D- Hot Pixels and Noisy Photos
« on: January 28, 2013, 06:05:52 PM »
Hey,

Recently I have been shooting long exposure photos with my 7D and I've noticed that even at ISO 100 my photos are becoming really grainy after the sensor is exposed for only a few seconds. I have also noticed that at 30 sec + exposures I have red and white dots ( i thing they are hot pixels ) showing up in my pics and if the exposure is going for 30 minutes +  You can barely make out the photo because the entire image is covered in red and white spots.

If someone has had a similar issue or know what could be the problem help would be much appreciated.

Cheers,

Remy.
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7D- Hot Pixels and Noisy Photos
« on: January 28, 2013, 06:05:52 PM »

Drizzt321

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Re: 7D- Hot Pixels and Noisy Photos
« Reply #1 on: January 28, 2013, 06:16:28 PM »
Have you enabled the long exposure subtraction method? This takes another exposure at the same length, but without actually triggering the shutter (or manually put the lens cap on and do it yourself in post). This basically takes a shot with the sensor without actually letting any light hit the sensor so it can use subtraction to remove much of the noise which can occur during a long exposure.

However, if they're showing up all over the place, that doesn't sound good. I don't have experience with the 7D, so I don't know if this is typical for the 7D.
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Jaguar2012

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Re: 7D- Hot Pixels and Noisy Photos
« Reply #2 on: January 28, 2013, 07:54:58 PM »
Hi murray09,

You can have a look at the following thread, Another users were having same challenges as you do.

http://www.canonrumors.com/forum/index.php?topic=1074.0

Which basically is to put lens cap on your camera, manually select Sensor Cleaning and once mirror have been flipped over to expose Sensor, wait 10-20 seconds and turn camera off.

You can find a more detailed  explanation on here:

http://forums.dpreview.com/forums/post/34537928

This method worked great on my 1D MK IV with a hot pixel. now i dont have any !

I hope you find it useful

Regards,
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jrista

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Re: 7D- Hot Pixels and Noisy Photos
« Reply #3 on: January 28, 2013, 11:25:46 PM »
First off...can you upload some sample photos somewhere so we can see the effect?

Owning a 7D myself, and having done some long-exposure star trails shots about a year ago when I first got it, I can at least state that I have not encountered the same issue. At least, not at ISO 100. On longer exposures, if I expose for minutes rather than just seconds, obviously FPN, or fixed pattern noise, begins to exhibit. Every digital camera has FPN as they are the result of tiny physical defects that affect charge buildup and reset for the affected pixels. They are usually called hot pixels, and as exposure time increases beyond a certain threshold, they become increasingly apparent. Most RAW editing software can easily identify and eliminate hot pixels, either automatically with the demosaicing algorithm, or via the NR tools.

If you are really seeing excessive noise at ISO 100 after 30 second long exposures, or if the hot pixels are particularly bad, it sounds like you may have a bad sensor or something. Noise will usually increase as sensor temperature increases, but not so much at ISO 100 that you couldn't see the image at all. Enabling long exposure noise reduction in the camera will double the exposure time, but it can automatically remove readout and FPN from the image as it saves it to the CF card. If you shoot a 30 second exposure, after the shutter closes the camera will expose a dark frame for another 30 seconds with the same exposure settings, read out a bias frame sensor at 1/8000th ISO 100, and combine all three images to remove bias and sensor noise in the final image.
« Last Edit: January 29, 2013, 01:12:01 AM by jrista »
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Mt Spokane Photography

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Re: 7D- Hot Pixels and Noisy Photos
« Reply #4 on: January 29, 2013, 01:33:33 PM »
Temperature can do it, cool temperatures work better, but some sensors may be more prone to noise.  The long exposure noise reduction is intended for reducing noise with long exposures, but it doubles the time to capture a image.

murray09

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Re: 7D- Hot Pixels and Noisy Photos
« Reply #5 on: February 01, 2013, 02:51:59 AM »
Thanks,

I will try these suggestions!
Canon 7d | Canon 1d mk ii N | Canon ef-s 10-22mm 3.5 - 4.5 | Canon EF 24-70 2.8 L | Canon EF 50mm 1.8 | Canon EF 70-200mm 2.8 L IS ll | Canon 300mm 4.0 L IS | Canon 430 ex ii | Canon 430 ex

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Re: 7D- Hot Pixels and Noisy Photos
« Reply #5 on: February 01, 2013, 02:51:59 AM »