nilsonium wrote:John Richard wrote:Secondly, you ruin the lens for use on other cameras.
Just so people don't take this the wrong way, if you remove the shim like I did, you can still use the lens on a canon DSLR, AF is fine, the focal lengths markings on the barrel are just shifted. And, as mentioned it won't maintain focus while zooming. But swapping in a thinner shim would go a long way to correcting this. Simply removing all shims is a bit of a sledge hammer solution...
Just so people are forwarned, I am posting what the highly respected John Brawley warned elsewhere on the shim removal method of attaining infinity focus (I sincerely hope JB does not mind my quoting him here - but thought it an important warning):
"Guys.
What you're doing here is shimming your lens to the camera. In this case you're removing a single or multiple shims to do that. Even a single shim might look the same but be a different thickness. They are often colour coded for thickness.
You should also note, this is a job of a lens technician. As some have noted, some lenses have different shims...some have more than one. This is evidence that this job (adding or subtracting shims) is a very precision job.
Now that you've removed your shim, you lens is no longer hitting the standard FFD. You've changed it to make it work on one camera. They now most likely will have issues on every other camera.
You're also missing that cameras also have shims in their mounts. In BMCC's case these are set at the factory (thus also nixing the extra cover glass changing the FFD theory).
This means that there is potentially something going wrong at the QA stage, or that there is a mechanical or manufacturing issue where the FFD is changing after it's been set or the custom engineering tool BMD built to measure FFD on each camera is slightly outside the tolerance it needs to be...or it's something else.
We know that not all cameras do this.
We know that not all lenses do this.
We know that this particular lens has similar issues on other cameras.
BMD are working on it. Changing lenses like this is a pretty drastic step. You're making your lens unusable on any other camera (and unsaleable). You should know that often you can't just put a shim back in and expect it to be the same. The tension of the screws, the orientation of the shim.....even changing the orientation 180 deg can affect the way the lens performs. It's not unusual to need different shims to get to a different FFD for the lens after doing something like this.....
jb
(has shimmed many lenses and cameras in his time as a technician at a camera rental company)