Back focus issue with 58mm Noct on Canon 5D?

[erik_gould1]

Maybe someone else has encountered this: I've done some shooting with a Nikon

58mm noct on my 5D and I notice that focus is off, especially at close range. I

am shooting at full aperture. Strange thing is that when I use an Olympus 55 1.2

under the same conditions it focuses correctly. Likewise with other manual

lenses, like the Nikkor 85 1.8 and 50mm 1.4 that I have also tested, both focus

correctly. I just ordered a new focusing screen for the 5D, the one recommended

for manual focus, so I will see if that helps. I don't quite understand how this

can happen, unless the screen isn't the precise place, but why would the other

lenses work? Any thoughts? I think I've done enough testing to believe that it

is not just my eyes.

[fotograf]

that lens is very old, so I would assume there are possible incompatibility issues especially using it on a Canon digital body

[sal b]

On forums over at manualfocus.org, people have mentioned having to adjust some Olympus lenses on a 5D by removing the rubber focusing ring and moving setscrews to get proper infinity focus. Some do this with the camera tethered to a computer, because you need to check at 100% crop to do this successfully.<p>

 

You might want to ask on a forum over there to see whether anyone has done something similar with Nikon lenses. You'll need to register to search or post, but it's free and very quick.<p>

 

<a href="http://forum.manualfocus.org/">http://forum.manualfocus.org/</a><p>

 

HTH,<br>

Sal B.

[carlos_miami]

I'm having the same problem with my Noct-Nikkor/5D combo.

 

The lens was a breeze to focus accurately, until my shutter died and I sent the camera to Canon for repair.

 

Canon replaced the shutter and mirror box assembly, and when I got the camera back, the Noct-Nikkor had severe backfocus while all my other manual focus lenses (nikon 35/1.4, 105/1.8, 105/2.5, etc.) worked fine.

 

I too would like info on this subject so I can have my camera adjusted to the way it was before.

[robin_sibson1]

Clearly this has nothing to do with front/back focus as usually understood, which is a problem to do with AF operation and can vary from lens to lens. This must have something to do with the relationship between sensor and focusing screen. I seem to remembe reading that there had been some alignment problems with 5D screens (possibly just limited to early 5D bodies) and that in some cases the use of a shim was necessary to correct this. That may be worth investigating. As to why the problem is apparent only with one particular very fast lens, I suppose it is possible that none of the other lenses are quite as critical for focusing. But it might also be the case that this one lens is so fast that it is somehow beyond the design specification of the focusing screen (which is itself quite a sophisticated optical device), and that nothing is actually out of alignment. It may seem odd advice, but try focusing with the lens stopped down a bit, say, to f/1.4.

[steven_moseley1]

...I know, here is a wacky left field idea....why not use a Nikon lens on a Nikon camera....or maybe I'm just nuts?

[richard_bernico]

I had the exact same problem and I thought my 70-200 f/2.8L needed overhaul or my 5D, which had just had its entire shutter system replaced because the mirror fell off, needed to be returned for repair. Then I was in Borders book and found the following information ...

 

According to the Canon EOS 5D Digital Field Guide, pg 37:

 

"According to Canon's 5D manual, you can use a popular point-and-shoot technique of locking focus by half-pressing the Shutter button, and then moving the camera to recompose the image. However popular the technique, in my experience, the focus shifts slightly during the recompose step regardless of the AF point selected. As a result, focus is not tack-sharp.

 

"Some Canon documents concede that at distances within 15 feet of the camera and when shooting with large apertures, the focus-lock-and-recompose technique increases the chances of backfocusing. Of course, the downside of not using the focus-lock-and-recompose technique is that you're restricted to composing the images using the nine AF points in the viewfinder. The placement of the nine AF points isn't the most flexible arrangement nor are the AF points the optimal way to compose images. But manually selecting one of the nine AF points and not moving the camera to recompose is the technique that ensures tack-sharp focus."

 

Explanation: "The Speedlite AF-assist beam fires twice; first, a pre-fire to communicate focusing distance data to the camera, and then a second beam to confirm that the subject is in focus. Then the shutter fires."

 

I bought the book and the Speedlite System Digital Field Guide as well.