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Red spots on images with Canon 5DM2

John Forney , Apr 28, 2012; 02:57 p.m.

I have a problem with my Canon 5D Mark II. I was doing some astrophotography and long exposure pictures of star trails. After downloading them I noticed that there were stationary red, blue, green, and white dots. The more noticeable red ones were in the same place no matter where I had the camera pointed in the sky.
I went back and looked at previous pictures I took, including a 5 second exposure portrait of someone sitting in a room with natural light, and when I enlarged the image the red dots were also there in the same place. I ran some tests and the red dots become brighter and more noticeable the longer the exposure and are consistently in the same place. They are even faintly visible at 1/40 to 1/50 of a second. Cleaning the lens had no effect.
What can I do about this and what may have caused it?


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Bob Atkins , Apr 28, 2012; 03:05 p.m.

They are "hot pixels". They are normal and not considered a "defect".

They can be removed by dark image subtraction or there are software packages that can be used to remove them. Alternatively you can clone them out or better still, stop looking for them at 100% magnification on your monitor. It's very unlikely you would ever notice them in a print.

They are caused by things like leakage current. They are defects in the sense that they are not supposed to do that, but all sensors have them. You don't get 20 million perfect pixels unless you are very, very lucky. All sensors have most of their more serious "problem pixels" mapped out by the camera maker so you never actually see them.

Jamie Robertson , Apr 28, 2012; 04:28 p.m.

I may be wrong but I believe you can program the camera to map them out. You'll have to check that though. I have the 5D2 and mine has some annoying hot pixels too, I just haven't been bothered to try and map them out.

The only real problem with hot pixels is if you shoot serious video work. Then it can become a real pain as you can't clone them out.

Oscar van der Velde , Apr 28, 2012; 04:35 p.m.

try PixelFixer (http://www.pixelfixer.org). Take a dark frame to map the pixels and then run it on your raw files.

Marcus Ian , Apr 28, 2012; 05:18 p.m.

If it's still under warranty, Canon will remap the sensor for you free of charge. If not, I sure they'll do it for some cost.
If you look back through your archives, can you tell when it started? Or has it been clearly present since you owned it, and simply didn't notice it until now?

G Dan Mitchell , Apr 28, 2012; 05:23 p.m.

You might have either or both of two issues:

1. "Hot pixels" can be found on many DSLR cameras. Your raw conversion software will often automatically map them out after you run a few exposures through the software and you'll never notice them again unless you open your raw files in a very different conversion application.

2. You may be dealing with hot pixels that appear with longer exposures, such as the many-minute-long exposures that we often use to do star trail photographs. Here there are two solutions. The in-camera solution is to enable the "long exposure noise reduction" (a.k.a. "LENR") setting on your camera. With this enabled, each regular exposure will automatically be followed by a "dark frame" exposure of equal length during which the camera essentially creates a photo that contains only the noise and hot pixel data, which it then subtracts from the actual exposure to reduce/eliminate the hot spots. The downside is that each exposure now will require twice as much time - your 30 second image exposure will be followed by the automatic 30 second dark frame exposure. The upside is that for very long exposures your image quality will be great deal better. (There are some semi-work arounds that use a single dark frame exposure to map the hot pixels and then subtract them from multiple exposures in post.) The second solution is to create your star trails in an alternate way. Instead of making a single very long exposure, you make an automatic series of may shorter exposures and then use on of several possible methods of automatically assembling them to produce smooth start trails.


Scott Ferris , Apr 28, 2012; 07:55 p.m.

If they are true hot pixels, not just dark frame noise, they can be mapped out with a little known set of commands. This is from several sites but I believe this link is one of the first. It has been confirmed as working on many Canon DSLR's including the 5D MkII.

  1. Remove the lens and put the body cap in place on the camera
  2. Put the camera in to "manual sensor cleaning mode". Press the "Menu" button, then select the middle "yellow wrench" tab, then "Sensor Cleaning" then "Clean Manually". You will hear the click of the mirror coming up (so you *could* be using a swab on the sensor - but don't do that - leave the body cap in place).
  3. Leave the camera in this mode for 30-60 seconds.
  4. Power off the camera off - you should hear another click as the mirror drops down into place

That was it. Test the camera and see if the dead pixels are gone.

John Forney , Apr 28, 2012; 08:51 p.m.

Thank you for the replies. I have had the camera since around March 2010. Went I went back to my archived photos I noticed that the most noticeable spot first seemed to appear about three weeks ago. I was not really looking for small defects before. If I send the camera to Canon how much do you think it would cost to remap the sensor and would it really make that much of a difference?

When I use the long exposure noise reduction under the image command is it better to set it on ‘auto’ or ‘on’. Is this what Bob Atkins refers to as dark image subtraction?

What is the best method to assemble pictures together to reduce noise (to make longer star trails) as suggested by Bob Mitchell?

For the method suggested by Scott Ferris would this work if I left a lens on and kept the lens cap on and covered the viewfinder? Some of my things including my body cap have been packed by movers and I may not have access to them for a few weeks.

Matthias Meixner , Apr 29, 2012; 05:02 a.m.

I have a 60D and the process described by Scott also worked without removing the lens.

Marcus Ian , Apr 29, 2012; 10:15 a.m.

Since you had the same problem when NOT doing astrophotography, I wouldn't expect LENR to make a difference, I'd try Scott's suggestion, which, assuming it works (at resolving the problem manual clean works w/ or w/o the lens mounted), using the same method w/ the lens cap on should have the same result.

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