Manual Focus with XT/XTi

I've had my XT for a year and a half and while AF has been consistently accurate, I've always had problems with Manual focus since day one.

I would focus the XT and get a sharp image in the viewfinder, but the recorded picture would be front-focused by a consistent amount. I used a focus chart to confirm this. However, images taken with the camera's AF were spot-on - no problems, even down to f/1.4. The problem was too consistent and too precise to be accounted to operator error - but I wasn't able to explain why.

Now, I'd read about swapping in third-party focusing screens (such as the Haoda and Katz Eye screens), and interestingly the review of the Haoda mentioned removing the copper shim (far left in this image) when installing their screen; it said you didn't need it. So, yesterday I removed the shim, reinstalled the OEM screen and tested the camera with my f/1.4-1.8 primes -shot wide open- and, surprisingly, Manual Focus is now much improved, almost totally accurate. 100% comparisons between the camera's AF and my manually-focused shots now only occasionally shows a very small amount of deviation, which I'm willing to say is operator error.

So what I'm wondering is:

• Has anyone else had the same kind of consistent problem with Manual Focus on their XT/XTi? (by comparison my 30D has flawless MF ability)
  
• Has anyone else tried removing this shim? With what results?
  
• Why would Canon place a shim in there that appears totally useless (or is the wrong thickness)?
  

As a side point, I've anecdotally heard that Canon only designed the XT to be accurate with 2.8 or slower lenses - if so, that might explain why this issue exists and went unfixed during the two visits my XT had to Canon's Service Centre..

EDIT:
It might also explain why I didn't notice the problem at first while using my F4 zooms - the more I got into using fast primes, the more obvious it became..

I have the same problem, hardly every use manual focus now

Uhh, MF "ability" is dependent on the user's fingers not the camera or lens. If you manually focus then what you see is what you get. The only way I know of that could throw this off is if your focus screen is out of alignment.

Then my focus screen may be a tad out, as I'm very good with the focus ring and the image look sharp in the viewfinder but the image is not focus on the point I did it.

We are only talking a tad for me, but the auto get's it every time so i'm not worried. I use single centre AF point anyway.

gooble wrote in post #3927226
If you manually focus then what you see is what you get.

That's true 99% of the time but not in this case; this appears to be an XT/XTi-specific problem. As I said, my 30D is dead accurate, as I imagine your 20D is. The issue with my XT seems to be a clear case of focusing screen miscalibration - I'm interested to see how many others have the same issue...

Raymate wrote in post #3927257
auto get's it every time so i'm not worried. I use single centre AF point anyway.

That was my workaround (other than buying a 30D ) - I use C.Fn.4-1 and center AF point.. even so, my now zero-calibrated viewfinder is closer to a true "What You See Is What You Get" image. YMMV.

What lens are you using? Is this problem only coming up with one or more of your lenses?

mellowd wrote in post #3927309
What lens are you using? Is this problem only coming up with one or more of your lenses?

The issue was most noticeable with my primes, especially at close working distances:
- 30mm 1.4
- 50mm 1.8
- 85mm 1.8

...but I'd also noticed it with my 17-85 and 70-200 at low apertures. The only lens where I hadn't noticed any problems was the 10-20mm, which is more-than-likely due to the immense DoF of an UWA.

AF has always been accurate with all the above lenses on both the XT and 30D; IMO eliminating any chance the lenses themselves were faulty.

Have you adjusted the diopter on the XT?

I also hardly can manualy focus my 400D with 50mm f/1.4 wide open. It appears sharp on viewfinder and not after shot done. I do not know what to do, I have been one opinion that my camera is OK, it's just very narrow DOF. Auto focusing always perfect

gcogger wrote in post #3927702
Have you adjusted the diopter on the XT?

...Yes. The diopter setting was not at fault. Good question though.

Pixel9ine wrote in post #3927198
As a side point, I've anecdotally heard that Canon only designed the XT to be accurate with 2.8 or slower lenses - if so, that might explain why this issue exists and went unfixed during the two visits my XT had to Canon's Service Centre..

EDIT:
It might also explain why I didn't notice the problem at first while using my F4 zooms - the more I got into using fast primes, the more obvious it became..

Well, unlike the XTi, 30D, etc. the XT wasn't designed with any higher precision focusing points for f2.8 and faster lenses. As a consequence, the XT's auto-focus isn't always quite accurate enough for narrow DOF shots. I'm not sure if this explains anything about your manual focusing issue though.

Canon's entry level dSLR models, however, aren't really designed for pro-level manual focusing -- the viewing screen isn't as bright as the semi-pro and pro models, for example. There is probably little call for tweaking XT view finder screens for precise manual focusing and there may simply not be any procedure or mechanism for doing so at Canon Factgory Service except in gross terms. This, I think, may be a very good reason for considering a camera upgrade in your case.

In my experience, my XT's AF has been absolutely accurate for static subjects - this with every lens I've used it with, from my own primes right up to a rented 300mm 2.8 - lenses whose razor-thin DoF don't leave much room for AF error. My issue was not with the cameras autofocus abilities.

Furthermore, while I understand the XT's small, dim viewfinder makes it difficult to manuall focus with ease (hence why there is a market for third-party screens), I found myself consistently misfocusing by a precise and measurable amount - something that can't be attributed to design inadequacies - rather, this seemed to be a precise, replicable error brought on by a precise, correctable miscalibration.

My shock and surprise stems from the fact that removing the copper shim - which I imagine served to calibrate the position of the focus screen - resulted in a more accurate (almost spot-on) ability to manually focus.

I'd still like to know if any fellow XT/XTi owners who experience the same problem have tried what I've done, and what the results have been. (Or if there are any adventurous enough to try it and check the results..)

JackProton wrote in post #3931070
This, I think, may be a very good reason for considering a camera upgrade in your case.

Not only have I considered it, I've been a satisfied 30D owner for some time now - a camera which has allowed for accurate MF right out of the box. I'm simply glad that with a little correction, both my bodies now have this ability.

Well, I believe its a possibility that the "misfocusing by a precise and measurable amount" to the degree you experienced may still be within the tolerences to which the XT was designed and manufactured. While you or I might find these tolerences to include an unacceptable degree of error at either statistical extreme, Canon still may have felt them acceptable for an entry-level camera. Considering the auto-focus issues I experienced with my own XT and the inability of Canon Factory Service to "properly" calibrate my camera after three tries, I have wondered more than once if looser design tolerences weren't part of the cost savings measures used to create such a relatively inexpensive but full-featured camera.

Do you think the shim under the focusing screen was intended to be used as an adjustment? Obviously not by the user, but perhaps by Canon service?

-js