You want a nice silky smooth focus movement? Then a good cleaning followed by an adjust are just what's needed.
First, a little "how it works". When you turn the focus wheel as indicated by Red Arrows, a gear underneath the wheel engages an idler gear highlighted by Blue Circle which then meshes with the cogs on the inner helical race indicated by Blue Arrow. Over years the grease used to initially lubricate this will have congealed into a semi-hardened paste.
Remove inner helical race by unthreading. When the infinity lock position is met, push down as indicated by Red Arrow to disengage and continue unthreading the helical race in direction indicted by Blue Arrow.
Keep a close watch while unthreading the inner race to notice when it comes clear of the helical. This will be the re-entry engagement point when the helical is mated back again.
You have decades of dried grease to cut through so you'll will have to used an appropriately strong solvent agent. I have a vented paint booth so I use Acetone
or Lacquer Thinner as my degreasing and cleaning solvent. What ever solvent you use proper ventilation, handling and eyewear precautions are a must. Enough said on that.
Scrub, scrape and clean with what you have. I find that these retractable brass brushes really help get the job done.
Usually cleaning will have removed any of the black paint on the internal surfaces and will have to be reapplied. I use an acrylic flat black hobby paint as it dries very quickly and is robust to handling immediately. Hobby shops that cater to Model Railroading or even Military Modeling are good sources for these paints.
Just a word on lubrication. I conducted a test using several different greases. Use a grease that will not “creep” or flow. I did this test several months ago where I placed a dollop of grease on a sheet of glass and left it. Here are the results. No slumping or running of the grease.
Re-grease the helical and reassemble in the reverse order.
When mating the inner helical race recall that relative position where the first thread engages. The outer helical race has three entry points so even at the worst you have a 1 in 3 chance of hitting the right groove. One way to tell you have mated to the right helical groove is to look at the infinity lock arm and you should see the machined flat that the lock arm rides in.
Remount the focus assembly with the proper shims you made note of earlier and proceed to: Checking and Adjusting Camera Working Distance.
June 24, 2007