28mm f3.5 SMC Takumar focus scale wrong

[Carriage]

I've noticed that my distance scale isn't quite right on my 28mm and am wondering if there's anything obvious that could be causing it. It seems to be reading a smaller value than the distance I am with a tape measure. It's not really an issue apart from if I want to do manual flash with a guide number. My 55mm f2 seems fine so I assume there's nothing wrong with the body. Is this just a tolerance thing? Could the lens be assembled wrong? The photos it takes are fine so I most likely won't do anything like getting it repaired, but if there's a simple fix that'd be nice.

 

[AgX]

Do the focusing mark and the infinity mark coincide at end-position?

 

[Carriage]

Yes.

 

[bernard_L]

No offense meant, but are you aware that distances are from film plane; there should be a marker on te top plate.

 

[Carriage]

None taken. I was fairly certain that was the case but I'm talking about error greater than that anyway. I just checked again and I'm getting somewhere between 1.5 and 2m (~1.7m) when I'm measuring 3m with the tape.

 

[ic-racer]

Search "Collimation"

 

[ciniframe]

Sometimes with a slowish, wide angle lens like that it is hard to determine correct focus on the screen. If the measured distance is 3m then place the scale at that distance and see if it appears more out of focus than at 2m. One of the problems with SLR viewfinder is not just a dimmer view with slower lenses but also more DOF that can make correct focus difficult to asertain on screen. At least, with my 66 year old eyesight I trust the scale more than the viewfinder screen for my wide and very wide lenses. With your longer 55mm f2 lens there is less DOF at moderate distances resulting in more 'snap' when the image comes into focus on the screen.

 

[Carriage]

I think it does appear more out of focus at the 3m marking but I did have difficulty being sure as you suggested.

 

[jochen]

Hello,
the most important thing is that the focus limit stop at infinity is correct and that the focus in the film plane is also correct. If not, the infinity focus stop has to be adjusted. This is not very complicated, every camera workshop with a collimator can do this, if you have some experience with lenses, you can make it yourself. Besides, this is a superb lens!