Focal Point Issue with Canon 7D

[andreasb]

<p>I use a Canon 7D and generally love the new focusing system is has. When shooting, I try to get a focal point right on the spot I want to have in focus so I have gotten used to flipping through my focal points in a hurry rather than focusing with the center point and then recomposing. Most of my subjects are moving to some degree (general photojournalism stuff) and I frequently switch between one shot and servo mode, usually with good results with two exceptions and those are the outside two focal points. I am talking about the extreme right and extreme left focal points when looking through the viewfinder, holding the camera in landscape mode. The other focal points work great but these two seem to give me softer, maybe even stranger, results. The quality of the entire image seems different. The color brilliance and contrast seem slightly reduced but this could be the result of the softness also. This situation seems independent of any lens I use.<br>

I doubt my equipment is malfunctioning since everything else seems to be working great. I am really just looking for a better understanding of what is going on here. If anyone has some insight, I would greatly appreciate it.<br>

Thanks for your help!</p>

[PuppyDigs]

<p>Mayhaps your outermost points are in need of calibration at Canon Service. I find my 7D extreme left and right points to be accurate but having differing focus accuracy between various AF points is not unheard of.</p>

[ljwest]

<p>Are you, perhaps, using a Tamron lens? There were/are issues with some lenses and outer focus points acting not as cross-type points. <a href="http://www.canonrumors.com/2010/11/tamron-lens-phenomenon/">Read more at this link, and see if it applies.</a> BTW, there's a lot more related to that issue on that site, and it may also include older Canon lenses, apparently...</p>

[andreasb]

<p>Thank you very much for your comments!</p>

<p>Larry, the link you sent me sounds like a reasonable explanation. I do have a Tamron 17-50mm lens but have not used it much in the last few months. Since most of my shooting was in very low light, I though I would try a Sigma 17-50mm with OS to see if it would help even a little bit. I have essentially replaced the Tamron with it. I also have a Canon 17-40mm lens that I inherited a short while ago. All three of my lenses have the same problem on the outside two focal points. I also have a few primes that behave similarly.</p>

<p>I thought all the focal points on the 7D were identical. Thanks for educating me. Most of my problems in life seem to end up ignorance related. At least I understand now and can find a way to work with it.</p>

[ljwest]

<p>All the FPs in a 7D ARE identical, are cross-type, and should all work the same. There seems to be a problem with certain lenses, however. It was first noted with certain Tamron lenses. Tamron, of course, reverse-engineers Canon's AF system to make their lenses work. But the problem later appeared also to affect certain older Canon EF lenses. I haven't been following it closely, so I don't know exactly where they are today, 7 months or so out from the initial observation of the problem.</p>