[salihonba]

Rangefinder calibration / adjustment on Polaroid 110B

Rangefinder camera needs calibration for some reasons, maybe caused by vibration, camera hit the ground, loosing screws...., anyway, if you found that the overlay images in viewing window mis-aligned or the photos are out of focus, it's time to check it out.

There is not much information about 110B rangefinder calibration on internet, the best I can find is from Option8, master of Polaroid camera conversion/ modification.

While Byron is a little bit different from other conversion, so it provides more options for rangefinder calibration, easier and faster to finish the job.

In common case, calibration can be done by turning two screws on the back of mirror, that is...

1. Focus at the infinity, then turn the screws, to align the overlay images in the view window,
2. Then focus at something near, then turn the screws, to align the overlay images in the view window,
3. Leave the focus between near and far to the cam curve.

Two screws adjust mirror's horizontal/ vertical movements. as image below shows, upper left screw adjusts overlay image horizontal to move left (clockwise) or right (counter clockwise) direction; Lower right screw adjust overlay image vertical to move downward (clockwise) or upward direction (counter clockwise)


It is not so easy to remember which turn to which direction, so I developed a 'Right Hand Rule' to help remembering it.


When you adjust the overlay image, and don't remember which direction screw should turn, use your right hand like this, thumb represents horizontal screw, index finger represents vertical screw, and they are now showing the direction if you turn screws clockwise!

Now back to the calibration procedure mentioned earlier, you see that no matter at infinity or at near object, only two screws available for adjustment. Isn't that funny if you align the image at infinity, then at near object requires adjustment too, won't it ruin the first alignment???

In many forums discussing about RF adjustment, people always puzzled in this dead alley, aligned image at one end, but the other is not, and then back and forth, drives people crazy, still in dead alley.

Actually there is another place to adjust the overlay image, it is the fixed screw in the middle, by loosing it a bit, you can make whole RF mechanical part turn, thus move the image horizontally, by tighten or loosing the screw, you can move the image vertically.


So there are two sets of adjustment for overlay image alignment, with one set at infinity, and other set for near object focus, thus won't ruin the previous calibration.

In theory this should satisfy all calibration required, but there is always exception. If you align both infinity and near end, but the adjustment always ruin the other one, no matter how you adjust, it just can't match both ends, in this case, it must be something wrong on cam.

(to be continued....)