Serious back focus issue with my 500mm f4, but only on my 7D.

CyberDyneSystems wrote in post #15700460
Let us know how you make out on the river.

Wasn't much action at the River so I didn't get a chance to see if it worked well or not.

gabebalazs wrote in post #15702297
Chris, maybe I missed it in the thread (I read the whole thing), but does your 7D need -16 MFA for all AF points, or just the center one. Have your tried AF points other than the center one? DO they all behave like the center one?

That's a very good question. I typically only ever use the center point on my 7D. I will take it out later today and try some other points to see what the results are. Thanks for the idea.

I ended up sending both the 7D and the 500mm in to Canon. The 7D just got a clean and check but they had to disassemble the 500mm and recenter an element that was out of adjustment causing the lens to backfocus. I guess it just wasn't showing up as back on my 6D. Either way, the lens works beautifully now! Just wanted to give a follow up on my thread. CPS took good care of me.

gabebalazs wrote in post #15702297
Chris, maybe I missed it in the thread (I read the whole thing), but does your 7D need -16 MFA for all AF points, or just the center one. Have your tried AF points other than the center one? DO they all behave like the center one?

SVTmaniac wrote in post #15766864
I ended up sending both the 7D and the 500mm in to Canon. The 7D just got a clean and check but they had to disassemble the 500mm and recenter an element that was out of adjustment causing the lens to backfocus. I guess it just wasn't showing up as back on my 6D. Either way, the lens works beautifully now! Just wanted to give a follow up on my thread. CPS took good care of me.

Sorry I didn't quite get it.
I thought pre the Canon service, on the 7D it needed a -16 or -18, but on the 6D O was fine.
But now it works fine on the 7D (assuming little if no MFA) but surely now it has a problem with the 6D?
Ie they brought forward the focus on the 7D so its perfect , surely now if front focuses on the 6D?
Or have I got the logic of this MFA stuff all mixed up! [my assumption being you said the corrective work was on the lens not the 7D body?]
(Thank god both my lenses seem sharp and as near as dam it 0 MFA, AS i'm sure I would screw this up.

Submariner wrote in post #15771306
Sorry I didn't quite get it.
I thought pre the Canon service, on the 7D it needed a -16 or -18, but on the 6D O was fine.
But now it works fine on the 7D (assuming little if no MFA) but surely now it has a problem with the 6D?
Ie they brought forward the focus on the 7D so its perfect , surely now if front focuses on the 6D?
Or have I got the logic of this MFA stuff all mixed up! [my assumption being you said the corrective work was on the lens not the 7D body?]
(Thank god both my lenses seem sharp and as near as dam it 0 MFA, AS i'm sure I would screw this up.

The lens originally was showing serious backfocusing on the 7D and it required about -16MFA to adjust but it wasn't consistent enough for me to be happy. On my 6D it appeared to work well but after digging into the problem a little more it was actually off on the 6D as well. The difference was that on the full frame I had more DOF than on the crop which helped to mask the issue.

After sending it in to Canon and after they tore it apart and re-adjusted the lens it now works perfect on both my 7D and on my 6D with 0 MFA required. The technician I spoke to said that one of the AF elements was out of place somehow. It was a 13 year old lens after all so I guess it was due for a service eventually. Either way it only cost me $188 after my CPS discount and now I have a practically new 500mm f4L IS lens again and I couldn't be happier.

Here is a shot after they fixed it with my 7D and 0 MFA I was about 13ft away at the minimum focus distance and shot this at f5 and I put the focus point right on the eye of the Rattlesnake. So as you can see the focus is spot on now

IMAGE LINK: http://www.flickr.com/​photos/cheising/859709​8778/

IMAGE LINK: http://www.flickr.com/​photos/cheising/860391​2910/

IMAGE LINK: http://www.flickr.com/​photos/cheising/859709​8354/

Lenses and cameras do need service and calibration from time to time... I'm glad it's worked out so well for you. The 500/4 IS is a fabulous lens. Enjoy!

Thanks for taking the time to explain, totally makes sense now.
Very pleased to hear it is all sorted out for you - and at a pretty reasonable fee.

Certainly looks good to me; and if you are like me, a real relief to see them both perfect at 0 MFA. So that leaves plenty of adjustment if it goes off over time.

Off topic...that is a great deal on the service! But what do you have to get to get the CPS discount? Do you have to be employed as a photographer or can you be just a hobbyist?

birder_herper wrote in post #15774831
Off topic...that is a great deal on the service! But what do you have to get to get the CPS discount? Do you have to be employed as a photographer or can you be just a hobbyist?

you have to own enough qualifying items...and pay a bit
http://www.cps.usa.can​on.com/about_cps/about​.shtml