Edit: question modified for future googlers after discovering it's an M not a W.

I recently bought one of the many varieties of tricked-up Helios you can find on eBay - fake anamorphic bokeh & purple flare.
It's also modded to focus to infinity on a Nikon F-mount.
It does pretty much what I expected it to do & I'm having fun making odd pics with it.

It runs fine in Manual mode on my D5500, aperture & focus rings doing as they should, plus 'guesswork' exposure.

One aspect has me puzzled, though.

On the underside there is a knurled knob with a red W [or M] on one smooth area. It only turns far enough to expose or hide that flat plane with the letter on it.
It doesn't appear to do anything, as far as I can tell.

Is it part of the original mount/clip/release mechanism, or does it serve some other purpose, even with the F-mount it now sports?

Helios 44M - W knob

  • Now there's an answer pointing out my initial error, I feel like I ought to fix my M/W misconception in the question for future Googlers. Any agreements/objections? – Tetsujin Sep 24 '17 at 12:51
  • Well, keep in mind that anyone looking for answers about it might also be seeing it as a "W"... the shape suggests it, as you point out. :) – junkyardsparkle Sep 24 '17 at 19:27
  • Is the letter on the part which extends outwards in the left upper part of the shot? – sharptooth Oct 3 '17 at 15:58
  • @sharptooth - yes. click the image for full-size... – Tetsujin Oct 3 '17 at 19:04
  • I submitted an edited version of this shot including a red arrow pointing to the part in question. I guess it's clearer that way. – sharptooth Oct 4 '17 at 9:32

That letter is not a W, but rather an M for Manual. Normally I would expect an A (for Automatic) on the opposite side of the slider. It is used to (de)activate mechanical aperture linkage to the camera. In position M the aperture ring directly controls the opening of the aperture. In position A it only sets the aperture value, but the aperture stays open until exposure. This is common on M42-mount lenses.

Addendum: The mount converter might be pressing down the spring-loaded lever that is used for camera control. In this case you would not actually notice a difference between the two settings.

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  • I'd considered it may be an M, as it's inverted compared to all other text on the lens, but had dismissed it because of its shape - much more like a W. I can take it then that this is simply 'no longer required/can be ignored' for any camera with no aperture motor anyway, even if it wasn't being blocked by the mount converter? – Tetsujin Sep 24 '17 at 12:31
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    Letters on the outside of a lens barrel are almost always placed for reading from behind the camera, as is the case here for both the switch and the aperture ring. In position M the lens will simply work the way you want it to. In position A something needs to press that lever unless the mechanism was disabled when adapting the lens for the different mount. So, the switch has no function for you right now, but if you ever sell it, someone might want to put it on an old camera. – ad42 Sep 24 '17 at 12:36
  • Since the lens is physically modified to achieve infinity focus on Nikon F-mount, there is no way it is usable on native M42 camera anymore, meaning A/M switch has no use anymore. – elkarrde Sep 25 '17 at 12:01
  • @elkarrde To me the image in the question looks like conversion was done by means of a screw-on adapter with a corrective lens, so it would be fully reversible. Not sure, though. – ad42 Sep 25 '17 at 16:26
  • @ad42 sure, if it's just screw-on adapter (with or without corrective optics), then there are no issues whatsoever, you're absolutely right. But if there were some kind of gender-change operations involved, it would probably be totally unusable on original M42 cameras (depends on how the gender-change was done), most probably with aperture pin constantly depressed, rendering the switch useless. – elkarrde Oct 2 '17 at 18:21

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