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
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
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
Lift out the rangefinder glass carefully and
set it aside in a VERY safe place.
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
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.
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.
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.
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.
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
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
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.
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
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
June 24, 2007