Problem with Sigma zoom

[tonyowen]

I have been given a Sigma UC 70-210mm f4 – f5.6 zoom lens fitted for a Canon camera.

The lens manually zooms in and out

BUT it does not focus. - The focus ring moves only a few degrees – I guess something is stuck somewhere

Any ideas/suggestions welcome

Regards

Tony

 

[tonyowen]

No response so far, so another try with further info.
1] Image sigma01 shows the name ring (??) which appears to be screwed in position - if so, how can it be removed??
2] image sigma04 shows the focusing ring attached (left); but with the focusing ring removed (right) there appears to be a narrow screwed-in section. Can this be unscrewed so I can access the linkage from what moves the focus scale and the focusing ring?????
regards
Tony

 

[shutterfinger]

1] Image sigma01 shows the name ring (??) which appears to be screwed in position - if so, how can it be removed??

Get some nail polish remover (acetone). Apply a liberal amount between the name/trim ring and the outer edge of the main barrel. Let it sit 5 to 10 minutes. Use a strip of rubber or a jar opening aid and put pressure on the ring at 180° apart and push counter clockwise 90° to the lens barrel. The front lens element will come out when the ring is removed and may have thin brass shims under it. Count the number of turns it takes to remove it and record for reassembly.
Take another picture of the end with the ting removed and post it.

 

[tonyowen]

Take another picture of the end with the ting removed and post it.

For ting I read ring. However I managed to remove the name ring but by gouging two holes in the ring' face. Even so it took a huge amount of torque to unscrew with severe resistance until it came out.
The attached image shows three equispaced screws (heads) that I guess need to be removed and then the inner tube can be removed. Between the outermost tube and the inner tube a lug can be seen that I guess permits focus.
regards
Tony

 

[shutterfinger]

For ting I read ring.

A typo that got by me.

However I managed to remove the name ring but by gouging two holes in the ring' face.

Something I would never do. I would have fought it letting acetone soak in longer, tried penetrating oil, or soft heat to get it loosened.

I tried to download your image and add markers for discussion but the text tool in PS will not work on the image and image size gives some strange dimensions.

Looking at the left of the image the first step down from the screws looks to be off centered. It should be even all around the barrel and is likely your focusing problem.
The screws have a locking substance on them so use acetone to soften or remove it before attempting to unscrew the screws or you will likely strip a head.
Removing the screws should allow the front of the barrel to separate from the main body exposing the focusing and zoom helicals.

That's when the fun begins. Focusing helicals usually have three starting points and getting it correct is basically trial and error until you get it correct. The zoom should be similar.
The ribbed piece in the center with the 4 notches is the retainer for the next set of lens elements and does not need to be removed.

Good luck!

 

[tonyowen]

Something I would never do. I would have fought it letting acetone soak in longer, tried penetrating oil, or soft heat to get it loosened.
Looking at the left of the image the first step down from the screws looks to be off centered. That's when the fun begins. Focusing helicals usually have three starting points and getting it correct is basically trial and error until you get it correct. Good luck!

I plead guilty by circumstances. I tried 'everything' before the final action of scarring part of the name ring. Even so there was a lot of screeching whilst the ring was being unscrewed - so some remedial action needs to be taken before reassembly.
Yes the screws are centred the angle of the image distorts things.
So, the helicals are multistart - no problem provided I'm careful and mark up the start positions. The zoom appears to be okay.
I'm now waiting for a new set of screwdrivers before the next move.
regards and thanks again for your help.
Tony

 

[AgX]

[Drilling holes in a front retaining ring/cover is...] Something I would never do. I would have fought it letting acetone soak in longer, tried penetrating oil, or soft heat to get it loosened.

Some lenses got such holes in there from the start. Thus drillling (perfect) holes for applying a spanner to me seems a perfect last attempt before trying anything that likely would scar such ring. I considered doing so myself in the past.

 

[shutterfinger]

Acetone dissolves the thread locker used in camera gear.
90% Isopropyl Alcohol removed oil and grease.
Lacquer thinner is an excellent degreaser/cleaner but will strip any painted/lacquered finish it comes in contact with.
Lighter fluid is the go to cleaner of shade tree repair people. You will never find it in factory authorized repair shops.
https://www.amazon.com/Finish-Line-...&qid=1542054941&sr=8-3&keywords=teflon+grease
is a good choice for camera gear if you don't have the manufacturers specified lubricant.
https://www.amazon.com/Tri-Flow-Squ...F8&qid=1542055146&sr=8-5&keywords=triflow+oil
is excellent where oil is called for in camera gear.

 

[AgX]

Lacquer thinner is an excellent degreaser/cleaner but will strip any painted/lacquered finish it comes in contact with.

This may be a terminology issue, but there are many different organic solvents used for laquers. Some are benigne concerning painted surfaces, some not.
On my workbench I got 5 solvents at hand.

 

[Svenedin]

@shutterfinger When you say "lacquer thinner" do you mean Xylene? It's amazing stuff for getting the sticky pads that hold on car number plates off and it doesn't harm modern (water based two-pack) car paint but it does horrible things to many plastics.

 

[shutterfinger]

 

[AgX]

As said maybe in the US that is a fixed term, here it is not.

 

[shutterfinger]

there are other types and not all are sold in california but those examples are what I'm refereeing to.

 

[tonyowen]

I've now taken out various screws and got to the focusing 'drive'. However, it appears to be very reluctant to 'unscrew- hopefully it has not cold welded.
\but as I try to unscrew it I'm obviously distorting the two rings - hence increasing the resistance against unscrewing
Pic attached
any comments/advise welcome

 

[shutterfinger]

Are A a set screw that adjust tension on the helical? If so loosen or remove them.
Place B down and coat the groves in C with penetrating oil and let set for a day or two.
If it does not come loose submerge it in Naphtha for a few hours.

 

[tonyowen]

Are A a set screw that adjust tension on the helical? .

Thanks for reply, no 'A' is one of the two drive lugs that enable the focusing motion. I cannot see any screws or other methods of tightening the thread tension.
I'll put some WD40 on the tread and hopefully it might ease the restriction.
regards

 

[shutterfinger]

WD40 will dry out and leave a sticky residue.
If the helical section C backs out/separates from A/B section then I would separate it and clean the groves on both pieces.

 

[tonyowen]

WD40 will dry out and leave a sticky residue.
If the helical section C backs out/separates from A/B section then I would separate it and clean the groves on both pieces.

Agreed, but first I've got to get them apart and WD40 is the option i have.
regards