Problems with lens micro adjustment.

[Swissy]

A friend of mine has asked me to help him with a problem he has with one of his lenses, it's an 18-50 f2/8 zoom, he has been using the lens for a while on a Canon 600D and has had no issues at all.

He's now bought a Canon 50D and when using the lens on this camera hitting focus is very hit and miss, he asked me to look at it and i micro adjusted it using the 'dot tune' method and have and got a 90% focus hit rate at 50mm, i had to set the focus in camera to -4.

He seemed happy so it's all good so i thought but when the lens is at 18mm the focus is nowhere near again, dot tune again at 18mm and now i had to set the lens at 0 (zero) to get decentish focus again.

I tried setting the micro adjustment to other settings between -4 and 0 but with no success.

So to sum up if he shoots at 50mm setting needs to be -4 and at 18mm 0 , i've not even tried checking what it's like at mid zoom settings yet.

Anyone come across this before? any suggestions please?

PS i have tried other lenses on the 50D just to rule out any problems with the camera, and the focus was fine.

 

[Mark twiglet]

Send the lens off! They can calibrate it! Has it been dropped and damaged???? Sounds like a lens element is wonky

 

[Swissy]

Send the lens off! They can calibrate it! Has it been dropped and damaged???? Sounds like a lens element is wonky

Funny how it worked fine on the 600D though.

It's not been dropped to my knowledge.

 

[nandbytes]

I don't think its a problem with lens or body, its just way the things function. This is a common problem with zoom lenses whereby you require different MFA values at the two zoom ends (simple google search will show many other similar cases). The common workaround is to stick with the value at the long end or perhaps try somewhere in middle of the zoom and see if it gives somewhat of a compromise.

More recent DSLRs do give the option of inputting two MFA values for zoom lenses (and interpolate for values in-between).

You could send the camera and lens in for calibration but I believe you run the risk of having your other lenses out of focus...

 

[odd jim]

Ah good old micro adjust! On a zoom, I wouldn't touch it, you'll always be out somewhere when you micro adjust a zoom.