Sigma AF 3.5/14mm II cleaning attempt

[stevemark]

Both versions of the Sigma 3,5/14mm are prone to fogging and even getting oil drops on an inner surface of the lens, resulting in low contrast images and haze.

Here are the two versions - this thread is about the right lens (version II):



And here's the problem - lots of small oil droplets on an inner glass surface:



OK, let's begin. Since there's no abvious starting from the front we have to begin at the rear end, removing the bayonet screws. I used some acetone to unblock them:



Then remove the screws for the electric contacts:


Now we can remove the bayonet mount:


View onto the remaining lens:


Next set of screws (beware of the red loctite => remove with acetone!):




These are the screws (not equal length!) plus the small U-"ring" for keeping the focus gear in its position:




The brass plate is removed:




Silver looking part removed:




Large screw (aperture mechanism guides) removed:


Next part of aperture mechanism transmission removed:




Next set of screws removed:


Next ring comes off:




Shims removed:





Electronics removed:




Rear baffles removed:




AF gear removed:




Focusing ring removed (middle screw only!):






Rear protection ring removed:






Rear lens element removed (remove the three screws; only one shown here):




Aperture mechanism now is visible and accesssible:


Sadly, it turns out that the the polluted lens surface is NOT just in front to the aperture (the aperture mechanism is completely dry and works perfectly). We'll have to dig deeper ... into the front element.

[stevemark]

I'm continuing to remove the remaining "transmission gear" for the aperture mechanism:









Then I'm stuck. The entire front part now seems to be one massive block. Now screws are visible, and I assume that ons should be able to remove the entire remaining aperture mechanism simply by turning / screwing it out ... but it doesnt work, not even after applying lots of acetone.

then I notice two small holes near the front of the lens. They are threaded, and it seems that there are screws inserted from the other side.


BUT on the other side there's only the large huge bulbuous front lens. No screw heads visible at all!!


SInce there are no crews visible now, I'm a bit lost. I can't unscrew the buil-in lens shade, I wasn't able to unscrew the front lens, and I couldn't do anything from the rear, in spite of lots of acetone.

Any suggestions??

Thanks

S

[BrianSVP]

This thread seems to have the info you need:

https://www.flickr.com/groups/1052301@N24/discuss/72157644071963297/

[stevemark]

[RokkorDoctor]

[BrianSVP]

From experience with the Mini and Super Wides, I can tell you that, as in your experience, it's not typically the element adjacent to the blades that fogs on them.

On some lenses, such as some of the Canon FDs, there are rubber gaskets that can outgas and cause condensation like this, but the Sigmas don't typically use them, so it seems to be something else. It's always the same element that is affected in any given model, so it may even be something in the particular coating on that element that is breaking down? It definitely occurs on air-exposed surfaces, so it's not cement separation that causes the milkiness.

It's also not always cleanable, often leaving a milky discoloration even once the droplets are removed, so the coating is definitely either degrading itself or is being degraded by whatever the liquid is. It could very well be that the person in the thread ran into this.

[stevemark]

[RokkorDoctor]

I have seen a few lenses that have a similar issue.

The Minolta MD 35-135/3.5-4.5 seems to have a similar problem; many of those I have seen developed droplets & haze on the inside surface of the rearmost element.

From memory I have once seen a diagram of the later Minolta AF 35-105/3.5-4.5 which is very similar, and that had an "anti-fogging compound" indicated around the perimeter of that last lens element (possibly some form of sealing compound). I do remember that as it caught my eye at the time, given the numerous fogged-up rear elements I had seen on the nearly identical MD 35-135 lenses.

I suspect that depending on lens glass composition, polishing method and coating composition some lens surfaces can exhibit hygroscopic behaviour. Many temperature fluctuations together with a not perfect hermetic seal could then lead to condensation inside otherwise apparently perfectly sealed air spaces.

This is just a theory; outgassing of polymer aspherics may be another potential problem; both acrylic as well as polycarbonate absorb some moisture from the air.

[kiddo]

I'm just amazed of the amount of knowledge you guys show, seems like any lens would be so easy deal to work on
I do have an old trioplan 7,5cm 2.9 from folding Balda that shares same looking droplets , I was able to open but there were damages in the coatings (Schneideritis?).
Of course the age of this lens has nothing to do with this af lens,but the blades of that lens also were totally clean .
Definitely some coatings gotta be weaker than others ,I am curious to see how will the story finish, as there might be also the option that would be cleanable.
By the way Steve, what JIS screwdrivers are you using? I've tried unlocking red loctite on yashica ml 1.4 with acetone with no succes, at least it worked in your lens. I understand there are many kind of red loctite ?

[RokkorDoctor]

[BrianSVP]

Just want to add that if you can find them in the UK, the plastic-handled US-made Moody Pollicis drivers are definitely worth a try. The ergonomics are just so much better than the typical metal-handled jeweler-style drivers. I've not tried the Engineers, but I've used that same Vessel set, and find the Pollicis significantly superior in both ergonomics and the durability of the bits, which are hardened vanadium steel.

Moody makes both fixed and interchangeable bit versions. The interchangeables are more economical, but can be more fiddly to use, so I prefer the fixed handle ones.

Fixed JIS:
https://www.micro-tools.com/collections/moody-tools/products/58-0405

Interchangeable JIS:
https://www.micro-tools.com/collections/moody-tools/products/55-0318

They also make pretty much any other style of driver bit you can think of.

[BrianSVP]

The Hybrid Aspherical hypothesis is an interesting one, but I'm not sure the dates line up.

The Sigma Mini-Wide II, which has this same problem in all versions, was introduced in 1986:
https://lens-club.ru/lenses/item/c_652.html#

This 14mm was introduced in 1991:
https://lens-club.ru/lenses/item/c_3421.html

Nikon supposedly introduced the first lens with a hybrid ASPH element, i.e. not a molded/ground glass or all-plastic) in 1991, in the AF Nikkor 28-70mm f/3.5-4.5D. Tamron, the first documented non-OEM to use one, started using hybrids in 1993 in their 28-200mm f/3.8-5.6. Note also that both of these lenses are lightweight zooms.

Now Sigma did definitely use such an element in the later 14mm f/2.8 EX DG ASPH (it's right there in the name!), but that wasn't released until 1998.

Could it be that Sigma was experimenting with this kind of thing earlier? Perhaps, but you'd think such at-the-time cutting edge technology would be something they would advertise far and wide, not something they'd sneak in without telling anyone.

[RokkorDoctor]

[stevemark]

I'm not doing lots of repairs, but enough to know the problem of stuck screws, and screwdrivers too brittle to manage the torque.
Interestingly, since I started to routinely apply solvents (usually aceton, occasionally WD40) to any slightly stuck screw there were no failures any more.

As I said - maybe I simply don't do enough repairwork ...

S