135mm ltm viewfinder question

[jagarch]

Hello,
I've got a Canon 135mm f3.5 in LTM with the viewfinder.
The viewfinder has a distance scale and turns around, from 5ft to infinity. What does this do? Is it just to remind yourself how far you are focusing? Or does it do something specific and mine is broken?
Also what does the spring in the mount do? Is that just to take it on and off?

 

[ruby.monkey]

Is it for parallax adjustment?

 

[FPjohn]

The ring gives correction for parallax error between the viewfinder position and that of the lens.

yours
FPJ

 

[venchka]

Right on. If you hold your eye to the viewfinder and turn the dial you should see the frame move. In use, read the distance off the lens and transfer that distance to the viewfinder ring. Newer bodies and viewfinders (at least from the VI-T onward) had a coupling pin. The viewfinder moved insync with the lens focusing distance. That's how my 135mm lens, body & viewfinder work.

 

[jmkelly]

On the Canon 135mm external finder, turning the ring just changes the angle of the finder barrel relative to the camera body to correct for parallax. You may not notice the movement since there are no framelines in this external finder.

 

[payasam]

If you look from the side you can see the finder tilting.