Sigma 45mm f/2.8 Lens Repair & Analysis | Salvaged Circuitry

Sigma 45mm f/2.8 Lens Repair & Analysis<br>[05.12.24]

I have a camera gear collection problem and as part of my personal 12 step plan, I restrict myself from purchasing functioning lenses. This sounds illogical, and it frankly is, but it's very hard for me to resist heavily discounted lenses. To keep my hat, I tend to only bid on lenses that are less than 1/4 of the going used sale prices and have little to no mechanical damage. In this case I've been eyeing the recently produced sigma I-series lenses that feature mostly aluminum construction. A broken 45mm f/2.8 lens popped up on ebay in January for a song and a dance, and I simply could not resist.

The auction was listed by an ebay seller that tends to have regular inventory of broken modern camera gear which is great from a repair perspective. Occasionally the seller will teardown equipment and sell parts, leaving me a bit uneasy about the internal state of the listed items for sale, but I took a chance and went with it.

Arrival

The lens came well packaged and on initial inspection, featured zero mechanical flaws. No scratches on the barrel or lens elements whatsoever. To properly inspect the outer lens elements, I use my oil free air compressor and thoroughly blow off any debris from the lens and properly clean both front and rear element with a kimwipe and lens cleaning solution. Eye glasses cleaner from the drug store is adequate for most external lenses. Isopropyl alcohol is another good alternative, but don't use on plastic lenses.

This is broken???

I mounted the lens to my Lumix S5 and with seemingly too much force, it clicked into place. The camera booted up fine and even displayed a live image, but no electronic controls worked whatsoever. None of the dials or switches on the lens responded to user input. The control dials on the camera did not register movement. Clearly, there was something electrically wrong with the lens. The control PCB is usually found on the rear of the lens nearest to the rear lens contact block. It would also provide a good time to investigate the very stiff lens mount.

45mm lens malfunction

45mm lens mounted

Tools

The barriers to entry on this repair are low. Most of these tools are pretty standard and generic at this point. The biggest expense besides the lens is filtered air, but even a compressed air duster can suffice. Note: Since most of the camera industry design folks are centered in Japan, the JIS screw is standard. Using a Phillips will work but it tends to wear down the heads on the JIS screws faster. Here are some of my go-to tools:

Kimwipes / lint-free lens cleaning wipes

Spray Isopropyl Alcohol (ipa)

Eye glass cleaner

Microfiber cloth

Nitrile gloves

Highly filtered shop air / oil free compressor

Tape

Sharpie

Scalpel

Plastic Spudger

Magnifier / optic

JIS x 2.5mm / Philips #00 screwdriver

JIS x 3.0mm / Philips #0 screwdriver

Disassembly

For disassembly, I orient the lens with the aperture mark facing me and the table front edge. The rear plastic beauty spacer around the rear element is removed first along with (3) black machine screws. Following, the two nickel plated screws that fixture the side of the plastic lens block terminal interface to the metal lens mount are removed. The screws are placed on double sided tape in an orientation that matches the lens orientation. This makes future reassemble substantially easier.

Beauty Ring Removed

Lens Block Screws

Next order of business, the lens mount bayonet and shims. The orientation and order of these shims matter so they deserve their own bit of tape. This lens had trouble mounting to a camera body so I thoroughly inspected the shims, bayonet mount back and the lens body for imperfections and surface contamination. I cleaned all surfaces with ipa and moved on. Note: be extra careful when handling the lens contact block flex cable.

At this point in the disassembly, the lens contact block can be freely removed from the control PCB. The contact block for L-mount features 10 terminals that connect to the control PCB via a flexible polyimide cable. This flex cable has a tendency to tear easily, especially if not handled carefully. Before continuing further with the teardown, take a multimeter and check the continuity of each trace. If there are visible tears in the flex cable, repair that first before continuing to diagnose any problems. I have another guide on how to make your own flex cables here. The flex cable metered out to be flawless, so I proceeded the teardown.

The rear CNC machined aluminum shell of the lens is up next. Two grounding straps are fixtured to the rear shell using nickel plated machine screws. The straps are oriented around the 2pm and 7pm clock position. A push-in switch flex connector is positioned around the 11pm position that can be wiggled out using a pair of tweezers. There are (4) black oxide self tapping screws that mate the shell to the center...