I recently picked up an unusual FED 50mm f2 (M39) collapsible lens - supposedly the Soviet pre-WWII copy of a Summar - and prepared a servicing guide which I thought I'd share. Best wishes for the new year! Due to the simple design of this lens, servicing is very easy. Lubricating the aperture ring • Locate and remove the two retaining screws in the aperture ring. • Note the unusual design of the screws, which have a long “tail” which passes through the lens tube and turns the iris ring. • Unscrew the aperture ring from the lens tube. This will expose two slots in the lens tube through which a portion of the iris ring can be seen, including the screw holes into which the long “tails” of the aperture ring retaining screws fit. • Find the f2 mark on the front ring and, using a pick, turn the iris ring so that the screw hole in the iris ring, visible in the slot under the aperture marks, lines up with the f2 mark. • Lightly grease the threads on the lens tube on either side of the iris ring slots. Screw the aperture ring on as far as it will go, then back it out until one of the screw holes in the aperture ring first lines up with the f2 mark. A small indentation on the aperture ring is the f-stop indicator; it should be at approximately the f4.5 mark. If not, unscrew the aperture ring and re-start it. Check alignment with the screw hole in the iris ring with a pick, rotating the aperture and iris rings together, and replace the first retaining screw. Check that the aperture ring moves freely and is operating the iris ring. • Repeat with the other retaining screw on the other side of the lens tube. Lubricating the helix • Remove the two stop pins in the base, the tall stop pin at the infinity distance mark and the short stop pin at the 1m distance mark. Unscrew the helix from the base. • Grease the helix and screw it into the base. When fully screwed in, the distance mark on the helix should be at the infinity mark on the base. • If not, unscrew the helix and re-start it. When it is correctly engaged, turn it back and forth several times to distribute the grease. • Screw the tall stop pin into the base at the infinity distance mark and the short stop pin at the 1m distance mark. Complete cleaning and lubrication, plus replacement of the packing ring around the lens tube • Collapse the lens and place it with the base of the lens facing up. The lens tube is attached to a brass flange which locks the lens tube into place when the lens is extended. Locate and remove the single retaining screw that passes through the lens tube into the brass flange. • Unscrew the brass flange from the lens tube. You may need to use a pair of channel-lock pliers to loosen the flange; take care not to bend or damage the “ears”. • With the flange removed, pull the lens tube straight forward to remove it from the base. • There is no need to remove the front ring to service the lens unless access to the lens elements or iris mechanism is needed. If you need to remove the front ring, remove the single retaining screw and unscrew the front ring. This exposes the retaining ring for the first lens element, which can be removed with a spanner wrench. • To clean and lubricate the aperture ring, follow the instructions above for removing the aperture ring from the lens tube. If this is the first servicing, there is undoubtedly old grease caked on the threads on the lens tube, the threads on the inside of the aperture ring and in the two slots in the lens tube, causing drag on the iris ring. Clean the threads on the lens tube before tackling the slots to keep as much debris out of the lens as possible. Once the lens tube threads are clean, remove the old grease from the slots manually; do not use solvents which might run into the lens. When all visible grease is removed, use a pick in one of the screw holes to turn the iris ring through its full range of travel and remove any grease exposed in the process. Keep turning the iris ring back and forth until all of the old grease is exposed and can be removed. Clean the threads on the aperture ring. • If the iris ring is stiff after all of the old grease has been removed, rub a very small amount of grease on the exposed portions of the iris ring and work the ring back and forth. Too much grease will contaminate the iris blades. If the iris ring moves freely, do not grease it. • If the front ring was removed, replace it now, because the aperture marks are needed as reference points for replacing the aperture ring. • Follow the instructions above to replace and lubricate the aperture ring. • To disassemble the base, remove the two stop pins, the tall stop pin at the infinity distance mark and the short stop pin at the 1m distance mark. Unscrew the helix from the base. • Examine the packing ring at the top of the helix. If the lens tube wobbles or there are scratches on the outside of the lens tube, the packing ring should be replaced. Remove the old packing ring from its channel in one piece if possible, to use as a template for its replacement. Remove any old adhesive left in the channel. With the packing ring out of the helix, clean the threads on the helix and the base. Deburr any rough threads with a Dremel wire brush and garnet paper. • Make a new packing ring out of adhesive-backed felt. Install the new packing ring in the channel, making sure the two cut ends meet smoothly without a gap or overlap. • Grease the helix and screw it into the base. When fully screwed in, the distance mark on the helix should be at the infinity mark on the base. If not, unscrew the helix and re-start it. When it is correctly engaged, turn it back and forth several times to distribute the grease. • Screw the tall stop pin into the base at the infinity distance mark and the short stop pin at the 1m distance mark. • Stand the lens tube on the lens end (with the lens cap on) and press the base assembly on to the lens tube. Press evenly to avoid pulling the packing ring out of its channel. • Screw the brass flange into the base of the lens tube as far as it will go. Check the location of the hole in the flange for the retaining screw so that it aligns with the screw hole in the lens tube. You may need to use a pair of channel-lock pliers to tighten the flange completely; take care not to bend or damage the “ears”. Replace the retaining screw. • Clean the front and rear elements. You’re done!