FED 2 rangefinder alignment woes

[mburns]

Oops.

Oops.

That's backwards, isn't it. The shorter arm at long distance makes for back focus as one focuses closer.

 

[Dez]

I now think that I am looking at a variable arm length design here - implemented by the curved surface of the cam. The purpose, I think, is to reduce back focus at a distance of 3 meters while also being accurate at 1 meter.

My FED-2 still has about .4 meters of back focus at a distance of 4.5 meters, but it has no back focus at 3 meters.

Yes, I think you are looking at a variable arm length design, but this radius is the distance of the point at the end of the cam from the pivot point, not defined by the curve of the surface, as was used in the later design. The earlier approach is somewhat crude, and interacts with the horizontal alignment at infinity too much, so presumably that is why it was changed. It sounds like your camera is still way out of adjustment, unfortunately. If it's correct at infinity and 3m but way out at 4.5m, you have something very strange indeed going on.

I suggest you reset things by setting the length of the cam as shown in my picture above, and adjusting it to be correct at infinity, then check where you are.

Cheers,
Dez

 

[Dez]

Here are pictures of the RF coupling arm on my three FSU cameras that have this old design. They came like that, and I have not altered them, as I have not had any focus problems with these cameras. As you can see the cam position is quite consistent.







Cheers,
Dez

 

[mburns]

'Will do. I was not previously concerned by this, because my Yashica GSN had the same quirk, and my Moskva-5 the opposite but less.

The back focus at 4.5 m is more like .3 m, when checking again, and it is right on at 3 m.

 

[Dez]

30cm of back focus at 4.5m is pretty severe. Is the RF accurate at infinity as well as 3m?

Cheers,
Dez

 

[mburns]

Yes, the focus is accurate on the crescent moon just now. At 4.5 meters, it reads 25 to 30 cm out. 3 meters is good, and 1.5 and 1.0 meters are slightly front focused.