why would focus (bf) change

KIPAX

KIPAX

Seriously Likeable
Messages
21,034
Name
KIPAX Lancashire UK
Edit My Images
No
I have a canon mkIV and i mostly have a 135mm f2 lens attached to it and sometimes a 35mm... I calibrated the 135 as at f2 you could tell the difference

all of a sudden the lens (after a long time) has suddenly started seriously backfocusing.. I mean a lot... but it seems all over the place.. not just one point.. "seems" to change or that could be how it seems..

why would it change out of the blue?
 
I take it it hasnt had a knock? Other than that, unless someone else has been messing with your gear I cant see why it should suddenly change?
 
It would suggest that somethings worn.

The variation would show depending on whether the lens was focusing out or in, causing any backlash to change.

Maybe you could try manualy winding the lens in and then autofocus, repeat it a couple of times and see where it focuses, then try winding it out manualy and doing the same.

It should show whether theres a gear thats on it's way out.

It could be the hole in the centre of the gear thats worn just as much as worn teeth.

At least it should prove it's a backlash problem or something else.
 
a knock was my first thought and to be honest i dont know when its gobe wrong..w ith light being good i had been using f5.6 and didnt notice until I needed f2 and its way out.. a wider dof (5.6) and you dont notice.. its both lens thus the camera problem :(
 
Have you tried them on the other body?

If its both it does suggest its the body. Maybe try resetting the micro adjust and go from there?
 
yes i have 2 mkivs and both no change on the other:(

just playing with macro adjust now.
 
Is the mirror by any chance dirty or dusty on the iffy one, just wondering also has it got a problem with the secondary mirror sticking ?
 
ChrisH said:
Is the mirror by any chance dirty or dusty on the iffy one, just wondering also has it got a problem with the secondary mirror sticking ?
Click to expand...

hhm how would i know test?
 
You could give the mirror a gentle clean with a lens brush. As for the secondary mirror try gently lifting the mirror witha cotton bud, you'l see the secondary mirror start to flip up. Hold the edge of the main mirror part open and using the cotton bud see if the mirror sticks up or flips back cleanly.

I'm just throwing ideas in the pot. If either mirror doesn't go back to it's set position then the AF will be off a little. You could compare it to the good body, see if you can see any difference.
 
I was scared just reading the Chris :)

I ahve done some testing and macro seems to have gone from plus +4 to -13 ... but then sometimes +4 works...its wierd and leads me to belive something is wrong in camera... elstree 3 day turnaround starts the day after they get your camera and no del saturdays.. think i need to drive to stoke and get lheimans to look at it :(
 
Yup not impressed with Canon at the moment they refused to replace the sensor in my refurb 1d3 even though it has a warranty. 141 hot pixels. They've just remapped it. Shoddy service as far as I'm concerned.
 
UPDATE

Camera had focus problems jumping all over the placea nd the mirror system replaced.. 24-70 had a new AF fitted.. both tested and work perfect.. But not together.. seems there is a problem wiht a 1dmkIV and a 24-70 as the 24-70 works perfect on other cameras but not on three different 1dmkIVs..so a diff 24-70 wass ourced and that wouldnt work on a 1dmkIV

1dmkIV of mine now on its way to canon to suss the problem and a loan body on its way to me
 
That sounds odd, it seems like it needs a reverse engineering solution to be used on updated bodies in a similar fashion to third party lenses!
 
odd jim said:
That sounds odd, it seems like it needs a reverse engineering solution to be used on updated bodies in a similar fashion to third party lenses!
Click to expand...

I would ahve imagined there would be a lot of 1dmkIV + canon 24-70 users about and the problem would ahve been noticed sooner.. seems ever so odd as you say..
 
replacement mkIV arrived this morning.. after changing the language to english i tested the 24-70 and same problems.. tested other lens and perfect

there does seem to be a canon 1dmkIV + canon 24-70L problem...
 
linhely said:
Maybe you could try manualy winding the lens in and then autofocus, repeat it a couple of times and see where it focuses, then try winding it out manualy and doing the same.
It should show whether theres a gear thats on it's way out.
It could be the hole in the centre of the gear thats worn just as much as worn teeth.
At least it should prove it's a backlash problem or something else.
Click to expand...

I repeat my recent update :)

24-70 had a new AF fitted.. both tested and work perfect.. But not together.. seems there is a problem wiht a 1dmkIV and a 24-70 as the 24-70 works perfect on other cameras but not on three different 1dmkIVs..so a diff 24-70 wass ourced and that wouldnt work on a 1dmkIV
Click to expand...


so the 24-70 works perfect on anyhting but a mkIV
 
I have a 1D4 and a 24-70mm, what are the problems you are having, is it not focusing correctly?
 
haaa Jim! :)

Just can't get a decent picture ..simple as that... the 24-70 has been in liehmans in stoke.. had a new AF system fitted.. has been tested on there system and been on various cameras working perfectly.. it doesn't work on either of my mkIVs.. doesnt work on the loan mkIV and doesn' work on one they sourced... but does work on other bodies they tried..

how wierd is that

bad picture as in.. very rough ..cant make out facial features on a subject 100 yds away taken at 24mm that sort of thing.. very poor
 
Last edited:
Well the mkIV went back to canon and I got my LOAN replcement through canon cps on the 19th may.. now 7th of june and no word from anyone :(

Still got a 24-70 here i cant use and still got a loan mkIV...

Not happy :(
 
KIPAX said:
bad picture as in.. very rough ..cant make out facial features on a subject 100 yds away taken at 24mm that sort of thing.. very poor
Click to expand...
I had a 24-70 that was incapable of focusing beyond about 10m at the wide angle end. It didn't matter what figure was registered on the focus distance scale, the lens would not produce a sharp image beyond close range, even when hard up against the infinity stop. At 70mm focal length there was no problem. Canon repaired the lens FOC, even though it was a couple of months outside warranty. It did actually take two attempts to repair properly. Once they adjusted the AF calibration. When I told them it was still not right, that's when they stripped it down and found replacement parts to be required. I think the inner lens barrel was one of the parts replaced. I don't recall what else.

It's quite probable (almost certain) that the problem was caused when the lens, attached to my 5D2, dropped from waist height onto a concrete road. I had never noticed a problem before the fall. In fairness to Canon, if I'd mentioned the fall they might have fixed the lens in one go, but I might have been presented with a hefty bill.

Now my experience wouldn't explain why your lens is only misbehaving on your 1D4s, but maybe there is an issue with the lens and you haven't noticed it for some reason on any other bodies. Can you get sharp images with manual focus? Does the focus distance scale bear an accurate relationship to the sort of distances you are shooting at, when shooting close up, or is it all skewed, because mine was right up the chuff before getting fixed.
 
Are the other bodies you are testing it on crop? If so it may be due to the more forgiving DOF on the 1.6 crop compared to your mk1V. Try it on a FF as if the problem is with the lens it will be worse than the MK1V.
My MA on my 24-70 is different at the long and short ends I do know that.
 
You must log in or register to reply here.
Back
Top