# Any Technicians? Canon Lens Reassembly Help (70-200 F/4)



## JoshuaP1993 (Aug 4, 2016)

Hello,

I have a 70-200 F4 L Lens which I have removed the front sections to clean and everything is almost perfect however there is a tiny amount of excess pressure when turning the focus ring now, specifically at 1.5m.

I'm quite sure that anyone who repairs these lenses often would easily know what the issue is, I don't believe it to be a major issue, just something simple.

I have checked and I cannot see any debris and I've been rather careful with everything. After a little testing I believe it could be related to the element near the front which moves up and down when focusing because when that is not inserted the focus is nice and smooth. It is when I insert that element with the 3 screws the issues occurs, perhaps it is related to the part which protrudes and inserts into the metal clip to allow movement of the element. 

Anyhow, any help would be much appreciated.


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## Mt Spokane Photography (Aug 4, 2016)

I have no idea as to your experience in disassembling and repairing lenses, but if there is a issue after you re-assembled it, I'd recommend taking it to a repair center. They might not want to touch it after it has been tampered with, but you can try. 

When disassembling a lens, it is extremely important that everything be marked and re-assembled exactly in the same orientation as it was originally. Some of the screws may adjust tilt of the front element from side to side (Centering), and if they are tampered with, its going to be a big bill for lens recalibration. Those spacers that the focus element or zoom element glides on are prone to damage, and will bind if cracked or missing. Sometimes a piece breaks and falls out so it might not be spotted as missing.

Different lenses have their own method of adjustments, and I'm not privy to them. I repair my own lenses, and have occasionally hosed a old one so that it ended up in my junk bin. I do sometimes remove front elements for cleaning, but never touch the adjustment screws.

You might drop a e-mail to Roger Cicala of lens rentals and see if he can point you to something he has published. Its often true that a teardown of one lens is nearly identical to another.

Good luck.


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## JoshuaP1993 (Aug 5, 2016)

Thank you for your response. 

Unfortunately I have little experience and wish I had never started this now, a lesson has been learned here!

1. https://i.imgsafe.org/3d3bf3150f.jpg
2. https://i.imgsafe.org/3d3c96145f.jpg
3. https://i.imgsafe.org/3d3c9e3d1f.jpg

I have been doing a little more testing and I have concluded that I believe it could be to do with the part shown in the first picture highlighted in blue.

Hopefully with those images you can make sense of the issue. The parts in the first image show what I believe you're referring to as the "bushings" and the element. If you see the other images you'll see that the element slides into the body and is held in place by 3 screws and 3 bushings. 2 of the bushings are the same (highlighted in green) however the 3rd is shaped differently (highlighted in blue). The 3rd one slots in the middle of the metal clip shown in the second image. This enables control the element to move up and down when you turn the focus ring.

If you look closely you can see that the part is shaped so one side is extended, I believe it needs to be reinserted in the correct orientation. I have tried several positions but I still have had no joy.

Kind regards,
Joshua


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## neuroanatomist (Aug 5, 2016)

JoshuaP1993 said:


> Unfortunately I have little experience and wish I had never started this now, a lesson has been learned here!



I found this package, inside was a big block of some stuff that looked like gray playdough, with some wires sticking out running to a little black box. There was a ticking sound coming from the box, that seemed weird so even though I'd never seen something like this, I grabbed some tools and started tinkering. 

Well, at least learning your lesson didn't blow you to bits. 

If you can't get it sorted, hopefully Canon Service can do so. Good luck!


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## Sashi (Aug 5, 2016)

Crickey, hopefully you get it back together perfectly.
I can't help much with the lens but feel compelled to advise you to never try the same with your engine if your car makes a strange sound.


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## TeT (Aug 5, 2016)

Try this link...

http://canon300d.uw.hu/Canon%2070-200%20F4%20IS%20repair%20EN.pdf

If you can find a parts list for the lens, it shows an exploded view

I hesitate to guess what you did wrong. Best I can offer is to suggest getting another copy and taking it apart for comparison ... or send it to Canon.


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## scottkinfw (Aug 5, 2016)

Sorry to hear you learned the hard way, but at least you are smarter now.

I'm not a lens person, but I would bet on an improperly placed or torqued screw/spacer or perhaps the lens was not replaced in proper orientation.

I would be concerned that use of the lens at all, including to see if it is "fixed" may be causing additional damage.

My recommendation would be to send it in to Canon. You may just get lucky and get off for just a few hundred dollars (USD).

If you are a CPS member, you may even get a discount (given the circumstances, or not).

Good luck.

Let us know how it winds up for you.

sek


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## AlanF (Aug 5, 2016)

Is there an equivalent of the Darwin Award http://www.darwinawards.com/darwin/ for those who foolishly attempt to "fix" their hi-tech equipment without knowledge or training?


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## rfdesigner (Aug 5, 2016)

I take it you've googled: canon 70-200 f4 disassembly

When I needed to pull apart my 28f1.8 I found a couple of videos online and it made a huge difference, but then primes are MUCH simpler than zooms.

Did you video yourself dissasembling the lens?.. if not that's a lesson learned.

Chances are you've got a shim out of alignment or got a couple of similar parts swapped. Perhaps one of the little nylon zoom guides has been overtightened.

I have no formal training in lens dissasembly, but I am an R&D Electronics Engineer & I've built/rebuilt a number of telescopes in my time and know how to align the optics on them.. My primary concern with pulling apart lenses is realigning the lens elements afterwards.. even if you can get the zoom smooth, I wouldn't concider passing it until you've taken some quick astro-shots at the short middle and long end of the zoom range and inspected the stars in the corners for equal amounts of coma (and that's the bodge-it way of checking lens alignment).


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## Mikehit (Aug 5, 2016)

AlanF said:


> Is there an equivalent of the Darwin Award http://www.darwinawards.com/darwin/ for those who foolishly attempt to "fix" their hi-tech equipment without knowledge or training?



They are now called 'Joshuas', for those where technical ambition far outweighs their technical ability. Ideally with the result being that the manufacturer ends up with significant new business with zero marketing expenditure
An associate award may be granted for those who could not afford official repair or replacement and found a perfectly serviceable alternative that highlighted they did not need the original equipment in the first place.


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## JoshuaP1993 (Aug 5, 2016)

Thanks for the helpful replies. 

TeT: Unfortunately I was unable to find much information from the link but thanks. 

scottkinfw: Thanks, yeah I believe the orientation of the bushing is the issue. There are only 3 and 1 of them is unique so I pretty much know their location, I just need to find their correct orientation and tightness and I should be okay. 

rfdesigner: As above, I believe it is just an issue with the 3 bushings which I have shown in the first image, nothing else. 

So my conclusion is this: whilst I have been daft, that is undeniable, I don't believe it is a major issue. The issue seems to be with the origination and tightness of the 3 bushings shown in the first image. 1 is unique so I am certain of their location. The only issue I have is knowing their orientation and tightness. 

I am hoping to find either a diagram, image or for someone to explain which origination that should be seated in then I only need to worry about the tightness. 

Thanks again for the advice, it is much appreciated, well the helpful ones anyway 

If anyone has anymore information with regards to the orientation please do let me know!


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## privatebydesign (Aug 5, 2016)

Email Roger here https://www.lensrentals.com/contact

He is extremely patient and experienced in this kind of thing, if they don't have one on the bench at the moment they will do in time.


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## Ozarker (Aug 5, 2016)

He goes where angels fear to tread. I don't want to meet him in a dark ally. :'(


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## JoshuaP1993 (Aug 5, 2016)

Thanks privatebydesign, you're the second person to recommend emailing Roger so I have done now. 

I have used this email: [email protected], I assume he will receive that as I gather he doesn't work alone?


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## privatebydesign (Aug 5, 2016)

JoshuaP1993 said:


> Thanks privatebydesign, you're the second person to recommend emailing Roger so I have done now.
> 
> I have used this email: [email protected], I assume he will receive that as I gather he doesn't work alone?



No there is a team there.

Either way, I have emailed him a couple of times and he has always been very helpful and answered personally.


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## TeT (Aug 5, 2016)

It is how the 2 pieces fit together and utilize the grooves in your 3rd pic that is probably giving you trouble.... 

They will go together 2 different ways, but only one will work. There is a tab of metal (?) that has to be in the correct position before you drop it in... 

The bushings in the first picture go in notch first.

Its been awhile since I broke one down


BTW: for those interested... that outer piece of glass on the 70 200 f/4 L is $43 shipped from Canon parts and is the easiest element on any Canon Lens to replace (in case of a damage etc...)


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## Mt Spokane Photography (Aug 6, 2016)

Roge Cicala re are you? He does post here upon occasion, and on the Fred Miranda forum as well. Brandon Dube (Bdube), who spent a summer as a intern at Lens Rentals also posts upon occasion and is very knowledgable about optics, I'm not sure if he is into the disassembly / repair though.


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## Bdube (Aug 6, 2016)

JoshuaP1993 said:


> Thank you for your response.
> 
> Unfortunately I have little experience and wish I had never started this now, a lesson has been learned here!
> 
> ...



I am not an expert on the mechanical repair of lenses, but I can provide some information.

The tracks in your second image are the zoom or focus cams. There should be rollers that slide in there; the ends are enlarged to make inserting and removing the rollers easier - they need to fit snugly to keep things aligned during focus/zoom. For this lens, a "collar," "roller," and "bushing" all refer to the same part.

In your third image, there are the tapped holes for the screws that hold the zoom/focus element in place, as well as the collars the screws need to slot through. The role of the collar is to distribute the force of the screw tightening, serve as an easily replaced failure point, and guide the lens in its focusing or zoom cam.

The bigger thing you highlighted in blue is a retainer for an adjustment collar, I believe (read: I am not sure). The flathead screw part of the special collar is the adjustment part. It is what lens designers call a "push around" compensator - it pushes the element around to adjust its decentering. The compensator is intended to serve as a set point, providing the position of the element in the barrel, and the two remaining screws tension it in place.

If the compensator is not screwed in at all, the focus/zoom should not turn at all, or barely, because it will grind against the external barrel.

Sorry I can't be of more help - I'm not an expert in this area, and in particular not very familiar with this lens. I do know that they tend to not manual focus when pointed upright and frequently come into repair for that, so Roger is certainly familiar with it.


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## JoshuaP1993 (Aug 23, 2016)

Apologise for the late response however I didn't realise the thread carried on as active.

If you followed what I had done, I emailed Roger and whilst he didn't reply personally they informed me that they were not in a position to help. 

Anyhow today I have tried again as I understood what the parts were for and where they go, what I couldn't work out is the orientation of the collar and how tight the collar and bushings needed to be. 

After only 2 attempts I have now successfully rebuilt the lens, there is no more rubbing and optically it is fine. Thank you again for those who tried to help.


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