How to ensure no front/back focus of Canon lens?

AndyYau · #1 07-26-2004, 01:13 AM

I have 300D and 1D MK II with Canon lens of 18-55, 17-40, 100 usm macro and 70-200 IS.

None of them have front/back focusing problem with the above two bodies.

Now I am considering 50 1.4 and 24-70, is there any chance for them to have front/back focus problem for the two bodies? Is this problem related to body or the lens itself?

And is there any quick and simple method to test 24-70? It is not easy to take so many photos in the shop.

I remember that the zoom ring of 24-70 is very tight at wide angle end.

Any help?

Andy

MarkRomine · #2 07-26-2004, 09:22 AM

Andy:

In case you have not seen this thread already I provide you with this link. It will not answer all your questions but it may give you some help. Back focus issues with Canon equipment is a huge problem with the wide angle zooms, 24-70, 28-70 and 16-35. Nearly every photographer's forum on the net has a slew of threads like this. It seems to occur with just about every model body made by Canon, but since Canon does not seem to want to step up to the plate and give us answers we can each only speculate as to the cause.

Backfocus 24-70

Mark

Eric_Chan · #3 07-26-2004, 09:43 AM

Andy,

In short, if you purchase new lenses and suspect they are not focusing properly, you can try a couple of things. One is to send the lens back and get another copy. Another is to send your lens to Canon Factory Service and they can adjust it to spec.

The zoom ring on the 24-70 is tighter at the wide end, but it's by no means stiff. It just has a bit more resistance, that's all. Still has a smooth feeling.

EC

Richard_Lewisohn · #4 07-26-2004, 09:49 AM

I've got the 50mm f1.4 and it front-focusses so badly that a building 30 feet away shot wide open is a complete blur. I sent it to CPS in the U.K, but it was so far out it was impossible to rectify. They said I could send it back to the shop (I bought it in New York). Instead I'm manually focussing.

Front/back focussing is a real issue with the 1D and 1Ds, and if you do have a lens calibrated for one body, it may be out for your second body.

I'd buy the lens and shoot some tests. If you're not happy with it, return it and get another.

These days, if the circumstances allow, I focus manually when shooting wider open than 5.6 on all lenses.

Good luck.

Richard Lewisohn

MarkRomine · #5 07-26-2004, 09:56 AM

Eric:

Another is to send your lens to Canon Factory Service and they can adjust it to spec.

Unfortunately this has not been totally successful fix with everyone, see the above thread, indicating that there maybe nothing broken with one's lenses and/or bodies but rather a problem with the design and function of the focusing system in Canon digicams.

Mark

AndyYau · #6 07-26-2004, 09:46 PM

It is so negative to EF lens!!! And why does not Canon do something?

Anyway, many thanks for all your information.

And finally, may I know what bodies you are using with focusing issue? It is the problem of 10D? What about 1D Mark II? It will be interesting to know.

Andy

Jonathan_Wienke · #7 07-26-2004, 10:49 PM

2 comments:

If you are having focus issues with multiple bodies and lenses, send everything in and have Canon check it all. Focus calibration is an interaction of body and lens, both must be calibrated properly for correct focus. Calibration errors in body and lens can cancel each other out. So if you have a back-focusing body and a front-focusing lens, they will work together just fine. But if you put a correctly calibrated lens on the body you get back focus. Sending the correctly focusing lens in for re-calibration will never fix the problem, since the lens id correctly adjusted. In this case, you must send in the miscalibrated body and lens that work together correctly for readjustment so that the correctly calibrated lens will work. But people would rather bad-mouth Canon than do this.

The commonly used technique of focus-recompose using the center AF sensor guarantees a certain amount of back-focus. The shorter the focal length of the lens being used and the shorter the lens-to-subject distance, the worse this problem will be. A lot of people are doing this, getting back-focused images, and blaming their camera when it is actually user error.

I have a 1Ds and a 10D, and 6 lenses. All of them focus properly. If the Canon AF system design was flawed, the odds would indicate that that I should have at least one lens-body combination with focus issues. I know Canon makes the occasional lemon, but much of the AF system "issues" can be traced to either user error or sending in the wrong item in for repair or adjustment.