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Cleaning & Repairs
Adjusting the Rangefinder

Rev.1

You've checked your Rangefinder and found it to be not accurate at one end or at both ends of the focus scale. Get ready for an all out complicated adventure.

Have a look at, How It Works - Rangefinder Operation to see a very simplistic view of the rangefinder in operation.

Consider this, that at infinity or any other exact lens barrel helical position, the moving plano-convex lens (1) has to be perfectly aligned to a setting at the very same distance that the lens barrel is set to. Meaning that when one focuses at something at 4 metres away for example the lens barrel marking should indicate the exact same distance. This maddening quest to have both the lens barrel distance marking agree with the viewed image is what will make this particular task one that will try your patience.

If the rotational alignment is out proceed first to Vertical and Rotational Adjustments further down this same page and do that procedure before horizontal adjustments are made.

The Simple Fix

Before you get all crazy and start taking everything apart you might try "The Simple Fix" first. Sometimes you get lucky and a small adjustment is all that is needed. Take the front chrome cover off first to reveal the rangefinder compensator mount screws as indicated. Loosen these two screws just enough to allow the compensator assembly to move.

You are attempting to make very small displacements of the compensator assembly and you will need some controlled method to do so. Take a small bladed screwdriver and insert it as shown. Pushing against the screw by rotating the screwdriver, you can make minute movements as in this example I am moving the compensator in the direction indicated by the Yellow Arrow. Keep a close eye on particular features such as the small gap to the left of the one screw indicated by the Blue Arrow to tell how much you moved the compensator.

Re-check the rangefinder distance accuracy again at .9m and infinity. Did you move the compensator enough and in the correct direction? If not, try again. If you can get the rangefinder adjusted with this method then you are very lucky.

 

It would make good sense once you have the rangefinder properly adjusted to lock it in place to guard against it from coming out of alignment from vibration or knocks. Here we see my daily shooter which was adjusted well over a year ago and then last week when I loaded it up to shoot for the day the rangefinder was out of adjustment. This camera rumbles around in my backpack every day or gets knocked about when hiking or biking.

Take a drop of ACC glue (Crazy Glue) and apply it around the head of the rangefinder compensator mount screws. To do this, dispense a drop of glue onto a plastic surface like a plastic bag and using the head of a needle or a piece of wire you can pick up a very minute amount of glue and precisely place that drop where you need it.

If this previous method didn't work, then proceed on to:

The Not So Simple Method

First you will need to remove the Top Casting and the Shutter Assembly to gain complete access to the rangefinder compensator mechanism from the inside of the body casting as shown. Remove the two screws that hold the rangefinder beam splitter glass in place.

Lift out the rangefinder glass carefully and set it aside in a VERY safe place.

 

Cleaning

Since you will have the rangefinder mechanism open and you will be making some wholesale changes to the rangefinder compensator it might make good sense to clean it at this time.

Take the rangefinder shield off by removing the three screws indicated. This will afford easier access for complete removal of the rangefinder compensator unit.

 

Remove these two screws and now the rangefinder compensator unit is free.

 

Lift the whole rangefinder compensator out of the camera body being careful not to knock it about with it's unprotected lens elements.

 

Remove the pivot screw and...

 

The two halves of the compensator come apart.

 

Before you go any further read the following warning: Do not disturb the front Plano-Concave lens from it's mount if vertical and rotational alignment of the rangefinder is good. Put a dab of semi-permanent glue over the existing glue at the positions indicated to reinforce it as the old glue is likely to be dried out and if left un-reinforced it doesn't take much handling to have this lens fall out on it's own. If it does, then you are in for a whole lot more work setting up vertical and rotational alignment. I use a glue that can readily be dissolved by acetone just in case I need to remove the lens from it's frame at any time.

 

The Plano-Convex lens is more robust but a couple dabs of semi-permanent glue at the following spots will ensure it does not move while cleaning and handling. When the glue is dry you now have complete access to clean the rangefinder lens elements. Re-assembly is the reverse with the only particular item to watch is the spring that loads the compensator lever.

 

Some Preamble

A little discussion on what we are effecting at a macro level is needed to better understand the implications of each step in the following adjusting procedure. Here we find the rangefinder at the infinity setting. Notice how the pin on worm gear arm (4) contacts the cam surface of compensator lever (3) at the toe end.

 

At .9m setting notice how the same pin is now contacting the cam surface at the heel end. Proper adjustment is required to have the full surface area from toe to heel of the cam contacted by the pin of the worm gear arm (4). All of the adjustments we make change the point at which the pin contacts the cam surface during the range of movement of the lens helical. The compensator lever (3) is spring loaded and will always press against the worm gear arm pin (4). 

 

The Horizontal Adjustments

There are three independent adjustments that can be made that affect the horizontal setting of the moving image in the rangefinder. 

  1. As we saw earlier with the Simple Fix, displacing the whole compensator in either of two directions as shown by Red Arrows will change where the worm gear arm pin contacts the compensator lever cam surface. A movement of the whole compensator to the right and the Plano-Convex lens rotates a little in the same direction. Conversely displacing the compensator to the left rotates the Plano-Convex lens to the left a little.

  2. Loosen the screw as shown by Blue Arrow will allow a rotational adjustment of the Plano-Convex lens without changing the worm gear arm pin/cam surface relationship.

  3. The range of rotation of the worm gear arm more broadly influences the contact position relationship of the worm gear arm pin with the compensator lever cam surface. Back during the Remove Lens Mount Helical document we stressed that the focus drive gear had to mesh with the lens barrel helical at a specific point. Changing the meshing of this focus drive gear by a tooth or more, with the helical will change the rotation range of the worm gear arm.

 

Mount the camera back into your test apparatus that you used to check the rangefinder at precisely .9m, from focus test chart to the film plane and carefully slip the rangefinder glass back into place. This focus test target was created by John Wilton and can be downloaded from his web site at: http://www.ragarecords.com/photo/index.html. As during the actual testing of the rangefinder accuracy you may have noted that the moving image didn't line up at .9m but which way was the moving image displaced from the fixed view image? Determining which way the moving image is out from the fix view image will indicate what your course of action is. 

At infinity the moving and fixed images were aligned. This will be our reference position to work from. On my example in Checking Rangefinder Accuracy the moving image was to the left of the fixed view image at .9m, or in other words, it did not travel far enough to meet up with the fixed image. A consistent methodology should be adopted rather than just haphazardly making adjustments in a random fashion. 

We will first get infinity to align and then adjust to get the .9m setting.

 

Since the worm gear arm is at full rotation the compensator arm can not be made to rotate the Plano-Convex lens any more. Therefore we need to loosen the screw by about 1 turn and rotate the Plano-Convex lens in the direction indicated. If you keep your camera in your test apparatus at .9m with the rangefinder glass in place you do have access to this screw and you can move the Plano-Convex lens while watching the result in the viewfinder window. Got the images to align? OK, tighten the screw.

It would probably be a good idea to make sure the two spring clips that hold the rangefinder glass are in place as we will be heading outside to check the infinity setting. How does infinity look? Probably it is out of alignment now. Make a mental note of where the moving image is in relation to the fixed image.

 

In my example the moving image did not travel enough to meet with the fixed image at infinity. This means the compensator lever needs to be deflected further in the direction indicated by the Yellow Arrow. To do this the whole compensator unit needs to be moved in the direction indicated by the Blue Arrow. Doing this will change the contact position of the worm gear arm pin on the compensator lever cam surface thus allowing the compensator lever to move. With a small screwdriver in hand you can work outside viewing an object at infinity and making small adjustments to the position of the compensator. 

Can you get the moving and fixed images to align? If you could not then we need to look at the rotational position of the worm gear arm at the infinity setting. If the whole compensator unit is displaced all the way in the direction of the Blue Arrow and the moving image still won't align then the worm gear arm needs to rotate to allow the compensator lever to move further in the Yellow Arrow direction. Notice how the pin on worm gear arm (4) does not contact the cam surface of compensator lever (3) at the toe end.

 

Check the rotational position of the worm gear arm at the .9m setting. There should be about 1mm between the worm gear arm edge and the metal bracket edge as shown. In my example I had less than 1mm.

 

To effect a rotational change to the position of the worm gear arm at infinity, we need to move the meshing of the focus drive gear with the lens barrel helical by one tooth as shown. Loosen the lens mount screws and lift the whole helical assembly up to free it from the focus drive gear. See our original reference mark on the focus drive gear?

Here's where things start to get repetitious and actually form part of procedure. 

(1) Go back outside and set the compensator such that we get alignment at infinity.

(2) Back inside to the .9m test apparatus to see how that looks. The images probably don't align. Use the method to rotate the Plano-Convex lens to get alignment at .9m.

(3) Go back outside and see what infinity looks like. If it is not spot on then make a rotational change to the position of the worm gear arm at infinity. Go back to step (1) and cycle through again.

You may already start seeing a relational trend by doing this repetition. Each cycle I took I started to realize that the moving image was getting closer and closer to being aligned at either end of the scale. The cycle again is: (1) Set and align for infinity with compensator, (2) adjust Plano-Convex lens rotation for .9m, (3) determine if more rotational changes are needed in the worm gear arm and then repeat the cycle.

I found that by going through the cycle of checks and adjusts I had to change the meshing of the focus drive gear by four teeth from the original reference mark before I got the moving image to align at both ends of the scale. It's picky repetitive work that will try your patience but hopefully you'll get it fall into place.

 

Vertical and Rotational Adjustments

The Simple Vertical Fix

As with any procedure there is always a certain amount of cheating you can get away with. If you rotate the rangefinder glass to point down slightly you can shift the moving image down and the converse works to shift the moving image up. How can you effect this "cheat"?

Simply grab the rearmost rangefinder glass support and bend it back to raise it or forward to lower. Its kind of crude and barbaric but it works. Just make sure that after bending it won't interfere with the full movement of the compensator lever. If you want to be more eloquent about this adjustment you could glue some shims to the bottom of the rangefinder glass either at the front or rear to coincide with one of these support pads.

 

Rotation Adjustment

If you were unlucky and the front Plano-Concave lens came loose or fell out while cleaning, or the rotation of the moving image does not align with the fixed image, then you will need a little patience for the following procedure.

Undo these two screws to get complete access to the front lens element. Damn, would you look at that, the old dried glue just cracked apart allowing the front lens to fall free...

 

Clean the front  lens and the frame to remove any remnants of the old glue. Any old glue left here will weaken the glue joint. As mentioned earlier, a semi-permanent glue is used to cement the lens into the front frame. If you place the Plano-Concave lens into the frame you will find there is a certain amount of play and movement the lens has. We need some method to temporarily hold the lens in place while we check the vertical and rotational alignment before we commit to gluing it in place.

 

Using dimensional strip styrene found at most good hobby shops serves well as a friction shim to hold the lens in place.

 

Here we see some .005" and .010" styrene used to hold this lens into the frame by friction. With some luck this will be a good rotational alignment on the first try. Re-assemble the rangefinder compensator unit and put it back into the camera body with the rangefinder glass. Don't worry about horizontal alignment at this time as we will just be viewing to discern rotational alignment only. Viewing at the cross on the focus test chart in our test apparatus we can tell easily whether vertically everything is in alignment. Probably not on the first try.

 

By using the same styrene shims of differing thickness a rotational displacement can be made in the position of the front lens. Rotating the lens right (or clockwise) will rotate the moving image down on the left side (or counterclockwise). So in a word, the moving image rotates in the opposite direction you rotate the lens.

If satisfied with the rotation adjustment just use the same semi-permanent glue to fix the lens in place and reassemble the rangefinder compensator.

 

Rear Plano-Convex Lens

Just a quick mention about the rear Plano-Convex lens. There is not too much that can go wrong with the alignment of this lens. All of the adjustments are done to the front lens. If for what ever reason it comes loose just clean up any old glue and slide the lens back into place under the two small tabs at the sides until the lens abuts against the two tabs at the top indicated by Red Arrows. Apply semi-permanent glue to affix in place.

 

June 24, 2007