bill_smith18

<p>Would focus screen misalignment also cause AF problems? Also is screen misalignment consistent with the fact that there is no out of focus condition at closer distance of 5 feet?</p>

<p>Thanks</p>

<p>Thank you. I did forget to mention that I did adjust the diopter. And tried adjusted to both with and without my glasses on. I also tried to reproduce a condition whereby an out of whack diopter adjustment would cause the observed shift in focus and I was not able to. In other words, a diopter shift was unable to result in an actual change in how I focused. Just whether or not the viewfinder would EVER be in focus.<br>

BTW, my prescription is relatively weak (-1.25)</p>

<p> </p>

<p>Although I have read through a bunch of focusing error posts, I have not found one that applies to my situation which I find confusing because the symptoms don't seem to match the theories. I would be interested in any insights.<br>

Equipment: 5D body, 70-200 f/2.8 L IS USM, 24-105 f/4.0 L IS USM<br>

This equipment is a few years old and has been babied (i.e. not abused in any way).<br>

I have run focus tests with these lenses using the focus test chart at a 45 degree angle. All tests at widest aperture and longest focal length. I performed some tests at close range (5 ft) and some tests further (say, 15 ft or so).<br>

At the close range, focus seems to be on the money.<br>

However, when I back up to 15 feet, they are backfocusing by about 30mm. For the 2.8 lens, that actually puts the point I was trying to focus on just out of reach of the closest edge of DOF.<br>

Here is the kicker: They are back focusing in both AF and MF. I understand that AF can have back/front focusing issues. But if I am focusing manually on the designated line yet the photo is focused 30mm behind that, what could be going on? I have reseated the focusing screen. But even if this was a focusing screen problem, the AF should not be affected by that right? OK, could it be a double problem? But manifesting themselves the same way? with both lenses? And why not at 5 ft? Seems that the evidence is pointing in different directions: Lens, Body, AF, Focus screen. UGH.<br>

I have yet to run tests at a further distance but I think I will do. I am going to find a picket fence and setup a 30 ft test.</p>

<p>To summarize:<br>

Why am I backfocusing at 15 ft but not 5 ft?<br>

Why am I backfocusing in manual focus more AND in auto focus mode?<br>

Why is this happening with both lenses?</p>