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.

 

I haven't quite given up yet but I am approaching that stage now. I spent a couple of hours tweaking the end pins today and whilst I can see focus altering on live view, I can't get my head around the science behind getting 3 pins to balance the focus. The centre of the frame seems the most sharp, but every other extreme of the frame is soft. I can get the centre to go out of focus but I can't get the centre to stay in focus when the extreme edges are in focus. Of course, Canon would have had dedicated rigs for this but I have a tripod and a letter from my insurance company to focus on.

I did get to a sort-of-acceptable image to then try the previously suggested cereal packet at 5 metres, but it was noticeably softer than the 100mm macro and even my cheap 18-200mm Sigma at the same distance. I will likely tinker as and when the mood takes me, but ultimately add a second hand 24-105 from somewhere like MPB to my Christmas list this year and keep the current one as a spares tub. If nothing else, it'll force me to use the 50mm prime and 100mm macro more.

 

That is what should happen, the adjustment you are making is for centering (at 105mm) and you should opt for a sharp centre whilst ignoring the edges.(centering for 24mm is done elsewhere)

I can't blame you if you give up as I think you should be proud of yourself for persevering this long. Even if you put it aside and never try again then at least you have learnt a lot, especially that YouTube guides can be a bit lacking in correct information.

 

Interesting, thank you Ray. I have indeed learned a lot and am continuing to learn. I will try again now that I understand it's only the centre of the image I should be aiming for with these pins. It's not over yet!