Repairing a Sigma 70-210 f/2.8

Guys, I'm so sorry and extremely FAGGED OUT. I spoke too soon and worse: gave a misleading description. I've just freed myself of this worthless job that has consumed a number of days from me after maybe 10 straight hours (since I posted my last message). I've now destroyed any hopes of re-selling the lens (which is what I do). The damage to metal, and sadly glass, is too much to make it salable. I mistakenly said the lens didn't have to be stripped down; WRONG. I had forgotten that what I was looking at as the rearmost elements of the lens were actually the rearmost elements of the INTERNAL CHASSIS upon which the rest of the lens parts are attached. I didn't realise how deeply I'd gotten into this thing. There's still another group behind this group that actually carries the aperture blades itself. While trying to affix the aluminum ring back, I terribly scratched the glass on that difficult part we're talking about. Reassembling, I see it is very visible up till f4 after which the aperture blades cover it. Most tragically and without reason, I disassembled the frontmost elements that are mated by a helicoild path. I introduced dust, grease and all into it and was not able to put both back when it mattered. After maybe 4 hours and really messing up the whole area, I managed to force them together with a huge amount of particles between and they're jammed in and can't be separated (I used a vice, hammer etc). The guilty glass element seems permanently foggy but I did my best and it is now much better, but not 100% clear. Itself even managed to drop on the concrete floor and I almost fainted; but it didn't break. Quite a thin glass by the way

Thanks for the update .
While things have gone wrong , it's still very helpful to know what's happened ( and how ) so it can be avoided .
Some photos of it in the process of dismantling to gain access to it would still be helpful .
As would your thoughts on if there would have been a better way of doing it .

As I said , I still need to clean mine up !

Cheers .

Hi everyone. I did send the only picture I took of the completely disassembled lens to someone on here by e-mail but he said he was no longer going to attempt any further to work on it since his wasn't that bad. For the last poster's situation: indeed the focusing lens group is in the very front part. To access it, you will observe that the entire front section has a wider diameter than the focusing grip part. Take your hands from the very front of the lens all the way to the end of that part with same diameter. At the end of it, before the focusing grip is a ring deceptively placed there to lock the front barrel in place. Looking from the back of the lens, turn the ring in the normal anticlockwise direction and voila, the front barrel comes off going further forward. The very first front glass is attached to the rest of the lens by just a black tape! I'm sure you can figure out the rest or else my response will get too long and unwieldy. Please let me know how it went

Yes, that's the one. It is difficult at first as when you tighten you grip, you may be squeezing it out of round. Try from a few angles. Normal direction (left).

When you get it off, the front barrel will come off (with the af version). The front element AND barrel underneath are held in place with tape. Do NOT take that tape off without first marking the front to rear sections or you will have difficulty aligning them back on.

Osi wrote: I was still waiting for your link to produce a picture to no avail. The picture policy of this forum is an Achilles heel

I uploaded my images to an external hosting service (Imgur). Perhaps the forum software mangled the link for you? Try going to i.imgur(dot)com/waX8gFs.jpg

pegelli wrote: Osi wrote: The picture policy of this forum is an Achilles heel Judging by the amount of pictures posted on this forum on a daily basis it can't be that hard: see here for instructions Btw, good luck with the lens repairs

As explained in March , it's simple and free to start a Flickr account to post images on here , and other places .

I also offered to put the images on my Flickr site and post them in this thread to help others in the future .
Not been taken up on the offer though . Shame .

Hi Osi .
That's a sickner losing your phone with all the images on , I know how valuable they are for reference .

I've P.Med you my email address .

When I get chance I'll get them on Flickr and posted here so anyone doing a search can find them .
Hopefully they will be of help to others .
Cheers .