EF 24-105mm lens repair - screws missing!

Long time no hear Sicarumba, have you given up ?

 

Haha, no sorry for the delay. I was struggling a bit with the eccentric collars as they are a little chewed which makes it tricky to tell when they are aligned. I was careful removing them when I disassembled the lens so it's possible someone has already been in here. I tried to line them up as best as I could but was nowhere near the sharp focus of your picture.

New ones are on the way and I should hopefully be able to try again in the coming days.

 

Ah, glad you are still here.
Are you doing your tests using autofocus or manual focus, for something like this I use manual focus with live view at x10 magnification to get the sharpest result.

 

I have the lens part-disassembled so none of the electrics are connected. I have a rubber band holding the focus arm and am manually tweaking the focus each way to see how sharp it gets. I am using live view at the maximum magnification, and every so often I am re-attaching my 100mm Macro to remind myself that no, that won't "do" and I have a ways to go yet.

 

Ray, do the eccentric collars only need to be positioned in one of the three orientations shown in your diagram or are they more of a ballpark start point and need further adjustment? Fitting the new collars hasn't made much difference and whilst adjusting the tiny eccentric pins on the front lens does shift the focus around a bit it's still night and day from your photo.

 

No, they have to be fitted in the stated positions only.
Perhaps your lens has had other parts replaced by someone else and this has upset the optical calibration.
Of course you also have to bear in mind the possibilty that your lens is just not as good at macro as mine appears to be, probably the best test you could carry out would be a mid zoom middle distant test and compare this to a similar known good lens.
Perhaps adjust the lens to the best you can get it and then set it at about 50mm at f4 and photograph sometthing like a breakfast cereal box at about 5mtrs then I could attempt something similar as a comparison.

 

Thank you, Ray. I hadn't considered the fact that identical lenses could have different results. I will fiddle with the end pins until I can get an even focus on my current test and then set up the scenario you have suggested. I'll also look through my previous photos taken with this lens (not many to choose from unfortunately) and see if I can recreate them to compare. Had I known about the fine tuning I am now attempting, I'd have taken a controlled 'before' shot prior to disassembly.