Wednesday, December 17, 2008

My 5DMII Black Blob testing

A friend suggested that I take a look at the website under the image critique forum. Specifically at an entry posted by Phillip Noll that talks about a black spot issue that has been found on the 5DMII with blown specular highlights. Just after looking at the forum entry and the links Phillip noted I received a call from my local camera store saying that my 5DmII came in. Perfect timing. ;^)
So, this morning I did some testing of the 5DMII, 1DsMIII and the 40D.

The gist is:
1. My 5DMII does exhibit the black spot behaviour but it was difficult to get it to occur.
2. My 1DsMII does not exhibit the black spot behaviour.
3. My 40D does not exhibit the black spot behaviour.
4. Please no one mention to my wife that it is unusual for a photographer to own all three of these cameras. Hey, at least I didn't buy the 50D! :^)

Actually not having a 50D leaves a hole in the testing (I'll have to mention that to my wife). The 50D shares the same ASIC (DIGIC 4) as the 5DMIII but I am jumping ahead a bit.

So, to me, and I know this is controversial and probably not correct as I have never designed a camera, it seems that the problem could be in the ASIC or the firmware. Oh please let it be in the firmware!
How did I come to this conclusion? The 5dMII and the 1DSMIII share the same imaging chip and the 1DSMIII doesn't exhibit the problem. So, I am thinking that the problem is not with the imaging chip.
If someone out there can perform the same test with a 50D (excuse me if this has already been done) and if there is no issue on the 50D then the DIGIC 4 can be ruled out. That would be great! With that we can say that it is most likely the firmware. Right? Yes I know I could be wrong so please feel free to let me know.

Here is the experiment I performed.
I placed a lamp with a Sylvania 75w 120v WFL J868 (a flood lamp I use for simple lighting) 10 inches behind a black sheet of construction paper that I had poked pin holes in (thanks to Andrew Yip for the idea) and setup the cameras on a tripod 7 feet away from the flood. I used my Canon 100mm F2.8 Macro lens for all images.
I found that at ISO 400 I was able to get "good looking" black spots at F5.6 at 2" (2 seconds). I could see them easily at F8 at 2" also. If I shut down the aperature beyond F11 I did not see the black spots. I did keep the exposure the same by changing the shutter speed to coorespond to the aperature.
At ISO 80o the spots were not as noticable and at ISO 1600 I didn't see them at all. This doesn't reflect what others on the web have seen and I admit my test was more limited... less real world. Also, I should mention that I turned all the Custom Functions II settings to Disable and still got the problem. I tried them all on and still got the problem.
I took the images with Large JPEG and RAW and got the problem.
And here is something I hadn't read yet, I was able to see the problem on the camera's LCD screen when I zoomed in all the way. That leads me to agree that it is not RAW processing that is causing the issue. Unless the processing of the RAW image data that is performed so that the image can be displayed on the LCD screen is causing the issue AND the jpeg processing is causing the issue. I guess that isn't too far fetched but I kind of doubt it is the culprit.

Is the problem bad enough for me to send the camera back? I am mostly a wildlife/landscape photographer so I don't think I will be hit too hard by the black spots... but I will be doing some real world testing over the next few weeks.

Has anyone performed this type of testing on a 50D?

Everyone has seen the images of the black spots so I won't post a bunch more... but here is an example from my testing.

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