Focus problems info - includes 5D2 and all Canon cameras

Started Dec 28, 2008 | Discussions thread
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Peter Gregg Veteran Member • Posts: 4,755
Focus problems info - includes 5D2 and all Canon cameras

Canon has a general focusing problem than most people don't know about, yet I feel more than half of the focusing problems fall into this "new" category of"soft" pictures.

The problem I am referring too is a more or less a "living room" lighting situation situation - also wedding receptions and similar lighting. With the flash on, you would expect the AF assist light to be giving the AF system plenty of light to work with. However this is not the case. Lighting that you and I would easily agree is low level lighting the camera does not think it is. We take pictures assuming the AF focus assist light is coming on and it is not.

The camera - all Canon cameras - have a threshold light level that turns the AF focus assist light on and it is simply way way too low. Therefore, many out of focus images are attributed to poor performance by Canon cameras or "soft" copies of lenses is actually more likely not enough light and the AF assist light not coming on.

I discovered this while comparing the Canon 5D Mark II with the Nikon D3 to see how well each focuses. When I was having trouble with the 5D2 focusing while sitting in my family room I took out the Nikon D3 to see how much better it would really be. It too had problems focusing in normal family room lighting in the house.

I accidentally happen to see while looking thru the viewfinder of the 5D2 that the AF assist light was not coming on, and it clearly should have been coming on as the lighting was lowlevel. I started to watch what was actually happening and to my surprise I found the AF assist light only comes n in conditions that most people would laugh at. In lower home-setting lighting with a few lamps on the camera thinks it has enough light and it just does not.

The Nikon suffers from the same trouble, but has a slightly higher threshold where the AF light comes on sooner but still not soon enough.

I took out the 40D and also the 1Ds Mark III and they too suffered from the same problem. I think a huge amount of pictures being nailed as out of focus and a poor focus system is simply the AF assist light not coming on early enough. Ironically at a wedding I was shooting I had a similar problem in a low light reception hall and noticed the AF light not working - and it should have been. I thought a setting on the camera had been changed and just moved on, but it was this culprit that was happening to me.

My point and shoot camera has a focus assist light that almost always seems to come on. So the folks with little P&S cameras are getting sharp pictures when we who shoot with DSLR's are not. And there is no setting in any of the Canon or Nikon cameras to force the AF assist light to always fire or to change the level of sensitivity for the AF assist light to come on sooner.

Tons of people thinking they can't focus accurately with fast 1.4 and 1.2 lenses are actually having a problem of not enough light to focus with. Even my F4 204-105L has the same problems as the faster lenses. Not enough light causes the focus system to miss the target enough affecting the shot's sharpness and we start to think we don't have "sharp copies" of our lenses. To prove the point just shine a regular old flashlight on the subject and focus and suddenly your "soft" L lens becomes tack sharp!! I did that to see what would happen and my 50mm 1.4 suddenly was tack sharp. If the AF assist light would come on the pictures would be sharp - i turn off the room lights and this caused the AF assist light to work and the shots with no room lighting were tack sharp at f/1.4 and when the lamps where turned on the focusing was all over the place. Easy to test this out for yourself!

Shame on Canon - and Nikon - for allowing this to be so. I have been sending in lenses to get calibrated over and over when the problem in lower light is not the lens at all, but no focus assist shows up to help focus accurately with such shallow depth of fields.


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