Repairing a Sigma 70-210 f/2.8

I would have liked to attach a photo, but have found no way to do it

beeton wrote: Rear group.... if I recall other similar lenses, 4 silver screws for mount, 3 small black ones for shroud, 2 slightly large black ones for contacts, rear cell should unscrew. They may have used locktite type products on the threads. Send a picture if you have one.

I've no pictures to hand , that's if I took any .
When I get chance I will dig the lens out and post some to i.d it , as well as stripping some of it down again to have another look at it .

The rear lens group has haze , hopefully just a layer on the innermost parts that will clean up , and not between two cemented pieces .

beeton wrote: Re 70-210 f2.8 APO, Gubbe. It's been awhile but thought I would ask. I am trying to deal with a rough focus as well, took the rear off up to the gears but stuck at that point. When looking inside the front, I noticed a plastic ring floating around so something has loosened up. I don't quite understand the front removal procedure. Did you say the front barrel unscrewed (the front element along with it)? This is on tight and I want to be sure before I try it again. Thanks.

Gubbe's last visit on Dyxum was December 2016

You might get a response from him if you send a P.M .
As long as he still uses the same email address he will get a notification that you have sent a message .
Good luck with your lens !

I'm still trying to figure out how to remove and separate to the rear lens group of a Sigma 300mm f/2.8 .
Only been about 5 years !!

Yes indeed. You've all seen my WTB thread and I already have a Sigma macro coming in, should be here any day now.

I'll go clean the front elements now, hopefully for the last time. ;)

CKsam you are a bloody genius!



I took pictures with all focal lengths and the exif data for the focal length from 150mm onwards reads like this:

150mm 160mm 135mm 120mm 120mm 210mm.

I twisted the zoom ring with considerable force for the last pic.



Incidentally, AF works fine up to around 150mm, only hunting beyond that. (Yes, I fixed the gear.)



BobJanes also deserves a big wet kiss straight on the mouth. I removed the rubber on the zoom ring and found a hatch that gives direct access to the slider that shorts out the contacts for the focal length. I just needed to clean the contacts and adjust the brushes a bit and voila! The focal length is now correct in the EXIF and there is no large-scale hunting left whatsoever!

Had I not known to look under the rubber, I would still be disassembling the zoom ring trying to find access to the brushes or spraying contact cleaner everywhere.



Right, about the gear. Like I said, I epoxied the axle and it came out fine. When screwing the plate back in its place I noticed that the gears turn very smoothly until the leftmost screw is fully tightened. I placed a small piece of very thin plastic under the corner of the plate and then tightened the screw and it's now smooth! Yes, the AF and MF are both now much smoother than they were before, I'd say they're almost like new!

Oh right, the epoxy. Although it came out well, I still didn't want to risk it since if the axle popped off again, it would be very difficult to re-attach. So, I cut off a piece of a toothpick, placed a piece of the same plastic on top of the gear as a cover and epoxied the stick so that it supports the top end of the axle. I also did it because I had broken the clip that holds the gear in place. Now the axle is supported from both ends and although the whole thing looks ugly, the axle will never come loose again. EVER.



Now all I need to do is clean the front elements and aside from the chip in the glass, this thing will be good as new!

Edited by Gubbe - 25 October 2012 at 20:40

Gubbe wrote: I'm wondering if that loose gear, assuming it came loose right away back when I last assembled the thing, could be the culprit in the AF hunting.

I agree that fixing lenses can be a lot of fun! It's hard to completely ruin them if you're careful. I love picking up dodgy broken lenses and getting them working again to (nearly) full capability.

The AF hunting could be due to bent sliding contacts on the circuit board/ROM bit. I had a similar problem when I took a Minolta 28-135 to pieces to fix something different. It's easy to bend the little contacts a bit on the reassembly without realising it. Worth a try, perhaps, but I could be completely wrong.

Mmmm...

Somehow I don't see Sigma frenzied to hire your services for their shop.
Nor a crowded, way overshot ebay auction...

But then, I'm oftenly wrong.