If the aperture ring of your Industar-10 (aka FED-10) is stiff or gritty, it probably needs to be cleaned and lubricated. Servicing this lens is a little more complicated than servicing an Industar-50 and, like that lens, it requires a spanner wrench. This walkthrough generally follows Jay Javier’s guide to “Getting Inside an Industar” and recycles some of my earlier walkthrough of servicing an Industar-50 where the differences between the two lenses are negligible. • Remove the set screw in the middle of the lens tube. • There is a black, thin-walled baffle pressed into the rear of the lens tube. It is held in place by three tabs in its sides which press against the inside of the lens tube. Pull the baffle straight out; a pick hooked into the cut-outs for the tabs may help. • With the baffle removed, two retaining rings will be visible. The outer retaining ring holds the lens block in the lens tube; the inner retaining ring holds the rear lens element in the lens block. • Remove the outer retaining ring with a spanner wrench. You may need to hold the aperture tab with one hand to keep the lens block from turning while the outer retaining ring is being removed. • There is a hole in the side of the front ring. Pull down the felt backing at this point to expose the front ring set screw. Unscrew the front ring set screw through the hole in the front ring. Unscrew the front ring from the lens tube. Once the front ring is free of the lens tube threads, it will pull the lens block out with it, so separate the front ring from the lens tube carefully. • Remove the shim(s) (if any) from the bottom of the lens block and set the shim(s) aside. Remove the front ring from the lens block by pulling the front ring forward. The aperture tab will catch against the inside rim of the front ring; just lift the opposite side of the front ring to clear it. • Remove the two set screws which are visible on the outside of the aperture ring. • Note the unusual design of the screws, which have a long “tail” which passes through slots in the lens block and turns the iris ring. • Pull the aperture ring off the body of the lens block. If this is the first servicing, there is undoubtedly old grease caked on the outside of the lens block, on the inside of the aperture ring and in the two slots in the lens block. The holes for the set screws which connect the aperture ring to the iris ring should be visible through the slots in the lens block, but they may be covered by old grease. As you are cleaning, keep an eye out for these screw holes, because you will need to find them to re-attach the aperture ring to the iris ring. • Clean the outside of the lens block before tackling the slots to keep as much debris out of the inside of the lens as possible. Once the outside of the lens block is 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 the screw hole in the iris ring to turn it carefully through its full range of travel and remove any grease exposed in the process. • 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. • Clean the inside of the aperture ring. If you find any corroded or rough spots, smooth them with fine garnet paper and carefully remove the sanding dust. • Turn the iris ring so that the screw holes are roughly centered in the two slots in the lens block (the exact position isn’t important – you just want to be able to find them easily). Lightly grease the inside of the aperture ring and the outside of the lens block. Push the aperture ring on to the lens block until the bottom edge of the aperture ring is just at the edge of the slots in the lens lock. Double-check the location of the holes in the iris ring against the holes in the aperture ring, slide the aperture ring the rest of the way on to the lens block and replace the set screws. If the set screws don’t seat properly, try rotating the aperture ring 180 degrees - the alignment of the holes in the aperture ring and iris ring might be slightly inconsistent from one side to the other side. Turn the aperture ring back and forth to confirm that the iris is operating properly. Remove any excess grease. • If the focus helix needs work, or there is dust inside the lens block that you want to remove by removing the rear lens element, now is the time to do it, before returning the lens block to the lens tube. • Set the front ring over the aperture tab, then push the lens block through the front ring. The front ring will fit loosely between the aperture tab and the aperture ring set screws. • Open the iris as far as it will go (you are going to use the f3.5 mark as a reference point for orienting the lens block correctly in the lens tube). • Replace the shim(s) (if any) on the bottom of the lens block. • Look closely at the threads on the back side of the front ring. You will see a hole drilled into the threads directly below the hole through the side of the front ring. • Look closely at the top of the lens tube. You will see a hole almost at the edge of the front opening. When replacing the front ring, this hole has to align with the hole drilled into the threads on the front ring. If you are unsure about the alignment, remove the lens block from the front ring and try test fitting the front ring to the lens tube. You may find that there is more than one starting point for the threads on the front ring to engage with the threads on the lens tube. Keep trying different starting points until you can consistently align the hole in the lens tube and the hole drilled into the threads on the front ring. • Place the lens block into the front of the lens tube. Tighten the front ring until the hole in the lens tube and the hole drilled into the threads of the front ring are aligned. Replace the front ring set screw and secure it with thread-lock compound. • Check that the iris is still fully open and set the aperture tab to f3.5. Hold the aperture tab with one hand and turn the lens over. Drop the outer retaining ring into the rear of the lens tube with the spanner cut-outs facing up. Tighten the retaining ring with the spanner wrench. Before it is fully tight, check to make sure that the iris is still fully open and that the aperture tab is set at the f3.5 mark. Finish tightening the retaining ring with the spanner wrench. Check the orientation of the aperture tab with the aperture marks; sometimes the lens block rotates a bit as the retaining ring is tightened. If it does, loosen the outer retaining ring, set the aperture tab to f3.5 and re-tighten the retaining ring. • Replace the set screw in the middle of the lens tube. This needs to be securely set to keep the lens block from rotating. • Replace the black baffle by pressing it into the rear of the lens tube until it seats against the outer retaining ring. The lipped end of the baffle goes into the lens tube first; the tabs point toward the front of the lens tube; the plain end of the baffle faces the rear of the lens tube. • Clean the front and rear elements. You’re done!