If the aperture ring of your Industar-50 is stiff or gritty, it probably needs to be cleaned and lubricated. Servicing this lens isn't complicated, but it does require a spanner wrench. This walkthrough generally follows Jay Javier’s guide to “Getting Inside an Industar”. I assume that a similar approach would work for an Industar/FED-10 or an Industar-22, but I haven't tried it yet. • Remove the set screw in the middle of the lens tube (not the set screw reached through the hole in the front ring – there is no need to remove this screw for servicing and it is extremely small and easy to lose). • 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 ring with one hand to keep the lens block from turning while the outer retaining ring is being removed. • Pull the lens block out of the front of the lens tube. Remove the shim(s) (if any) from the bottom of the lens block and set it aside. • Hold the body of the lens block and twist the aperture ring to open the iris as far as it will go. Note the position of the set screw which connects the aperture ring to the iris and mark the cut-out in the aperture ring through which the set screw is visible. Make note of the gap between the bottom of the aperture ring and the ridge half-way down the lens block. You are going to need to return the components to these original positions for re-assembly – a quick photo would be helpful here. Remove the set screw. • Unscrew the aperture ring from the body of the lens block. If this is the first servicing, there is undoubtedly old grease caked on the threads on the lens block, on the threads on the inside of the aperture ring and in the two slots in the lens block. Note that a stop screw is visible in one of the slots (it limits the travel of the iris mechanism); the hole for the set screw which connects the aperture ring to the iris should be visible through the slot on the other side of the lens block, but it may be covered by old grease. As you are cleaning, keep an eye out for this screw hole, because you will need to find it to re-attach the aperture ring to the iris. • Clean the threads on the lens block before tackling the slots to keep as much debris out of the inside of the lens as possible. Once the lens block 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 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. • 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. • Grease the threads on the aperture ring and the lens block. Screw the aperture ring on to the lens block until the base of the aperture ring just reaches the slots in the lens block. Look for the iris stop screw; when you see it, turn the lens block over to locate the hole for the set screw which connects the aperture ring to the iris. Keep this screw hole pointed up as you continue to turn the aperture ring; it will be visible only through the cut-outs in the aperture ring and you need to have a clear mental picture of its location. • When the aperture ring is screwed back to its original position vis-à-vis the ridge half-way down the lens block and the screw hole is visible through the cut-out that you marked, replace the set screw. Turn the aperture ring back and forth to confirm that the iris is operating properly. Remove any excess grease. • Replace the shim(s) (if any) on the bottom of the lens block. • If the focus helix needs work, now is the time to do it, before returning the lens block to the lens tube. • 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). Place the lens block into the front of the lens tube. Hold the aperture ring 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 indicator is set at the f3.5 mark. Finish tightening the retaining ring with the spanner wrench. Check the orientation of the aperture ring with the aperture marks; sometimes the lens block rotates a bit as the retaining ring is tightened. • 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!