monopix
Cam repairer
<<<<NOTE>>>>
I've been informed the pictures associated with this post and the one further down the thread have gone missing. As I seem to have lost the originals, I've retaken the pictures and rewritten the text. It's all posted on my Web site at http://www.z0g.eu/zi/zi_align.htm
_____
Well I couldn't resist doing some further investigation and decided to lift the lid of my ZM to see exactly what screws did what. This is what I found. Some of my conclusions haven't been confirmed as I don't want to make any unecessary adjustments to my ZM but I'm pretty sure what I'm saying here is correct.
In the other thread on this subject it was determined by several people that some adjustment screws could be found under the accessory shoe. I also added that some more screws could be found under the shutter speed selector.
Let's start with the ones under the accessory shoe...
To explain what these do requires some understanding of the rangefinder layout and I've done a couple of diagrams that I hope will help. First the general optical path.
On the far right is a prism which rotates when the focus is adjusted. Next to it is a glass block then some surface mirrors then finally the prisms that combine the images in the viewfinder. This is pretty standard stuff but the main point is that we have a prism that has to be rotated a little as the lens is focussed.
To achieve the linkage between the lens cam follower and the prism there is a series of levers thus...
The lens cam follower moves in and out and causes lever A to swing around point Q. Lever A engages the cam end of lever B and causes lever B to move back and forth also. Lever B is rigidly fixed to lever C which is hinged at P where the prism is mounted.
Now, look more closely at the join between levers B and C.
This is what you can see if you look below the accessory shoe. There are three screws that I've labeled X, Y and Z. X is the black, cross head, locking screw and Y and Z are slotted adjustment screws. In the centre we also have two fixed studs which are located in the curved slot in lever B. The two adjustment screws Y and Z are eccentric screws - that is, their heads are offset. If we unlock the locking screw X and adjust Y, lever B slides back and forth as the eccentric head of Y pushes it. The movement is controlled by the two fixed studs so lever B can only move in a slight arc.
If you look back at the previous image, you will see that moving lever B in this arc will alter the pitch of the edge along which lever A operates. The overall effect of this is that adjusting screw Y will change the amount that the lever B and C assembly moves for a given amount of movement of lever A. (with me so far???)
So what of screw Z? Well this isn't an adjustment screw as such. What it does is to keep lever B in close contact with the two fixed studs. If you look at the following pic you'll see that lever B is held tightly up against these studs so there is no slop in the movement. As far as I can see, that's all screw Z does.
You might also note in this picture the sealant on the locking screw. I think it's also worth noting that any attempt to adjust screw Y without first unlocking the locking screw will probably result in damage (I guess there's some people who didn't want to hear that). Similarly, if screw Z is adjusted you will either introduce slop into the system or you will cause damage by pushing lever B up against the fixed studs.
My conclusion to the above, and this is based also on what follows, is that screw Y is to adjust the close focus of the rangefinder.
So now, moving across to the screw I noted under the shutter speed selector. Here's what it looks like with the shutter speed dial removed.
The prism is located under the metal disk that can be seen near the screw. If you look either side of the black crosshead screw you can see two slots which is the slot of the adjustment screw. The crosshead fits down the centre of the adjustment screw and locks it. If the locking screw is loosened, and the adjustment screw turned, the prism will rotate slightly in it's mount. The adjustment screw is another eccentric type and rotating it moves the prism mount slightly. The effect of this is easy to understand and it will adjust the horizontal alignment of the rangefinder image.
Here's another pic of the arrangement with the camera cover off so it can be seen more clearly.
Also note the glass block next to the prism. We'll deal with that in a minute.
So, what we have are two adjustments of the horizontal alignment. My conclusion is that the first one, that can be found under the accessory shoe, is, as I said, the close focus adjustment while the one next to the prism is the infinity adjustment. I have spent some time pondering this as, at first, I wasn't sure which was which but I finally decided it was this way around when I thought of them as being a Gain and Zero control (something more familiar to the electronic guys amonst you of which I'm one). The adjustment under the accessory shoe effects the degree of movement of the prism for a certain amount of movement of the lens cam follower. I interpret this as a gain adjustment. The movement of the prism will have equal effect over the full range of movement so this is more like a zero of offset control. The question then is, at what point of the range do you adjust the zero control. In this case, I'm guessing that the arc through which lever B moves when screw Y is adjusted is centred on or about the position where lever A will contact lever B when the lens is on infinity. This is the only fixed or known point so it would make sense. If this is so, then adjustment of screw Y when the lens is set to infinity would have no effect so this must be the control for close focus and adjusting the prism is for infinity adjustment. Those people who have tried adjusting the screws under the accessory shoe and noted horizontal movement of the rangefinder image may disagree with this but, unless the locking screw was loosened before making the adjustment, the resultant effect is unpredictable as it would probably result from distortion or damage of lever B.
So how about vertical adjustment.
Look at this picture of the way the prism is mounted. Note especially the two strips of metal below it.
The lower of these two strips is the end of lever C. The prism is actually mounted on the upper strip of metal and, between the two, where I've put the red circle, is a small adjustment which moves the upper strip up and down. Although it's difficult to see in the picture, this adjustment has a pair of flats on it so it can be rotated and it also has sealant on it to lock it in position. This is obviously an adjustment and it alters the vertical alignment of the rangefinder image. The thing to note here is that this is not accessible without removing the top cover - but read on...
In the picture here you can see again the prism and the glass block next to it. In front of the glass block is an adjustment screw. This is another eccentric screw sitting in a slot.
The holder of the glass block is pivoted on the pivot that can be seen next to the screw. The effect of rotating the screw is to tilt the glass block on this pivot. Now this will effect the vertical alignment of the rangefinder image but it is quite a crude adjustment and I'm guessing this is not intended to be moved once assembled. I assume this because the mechanism has been very firmly sealed by the gunge that can be seen across the top of the mechanism above the screw. This gunge is set hard and there's no way of removing it easily. However, I did try turning the screw and, even with everything sealed up, I did get some vertical movement of the rangefinder image. This screw is accessible without removing the top plate, though it's difficult to get at, but it is a possible solution to vertical alignment problems. But an altogether, possibly, easier way to adjust the vertical alignment is to bend (yep I said bend) the end of lever C up or down. This end of lever C with the prism mounted on it is not supported at all by the body of the camera, it's only attached to the rangefinder assembly, so it will flex up and down a little. I found just by putting a little pressure on it either up or down, I could make small adjustments to the vertical alignment. It should be possible, I think, to do this via the shutter speed selector hole in the top plate so, as long as any error is small, this may be a quick and dirty solution.
So, that's pretty much it. I'm going to do another post with some more practical details of how to get at and do these adjustments for anyone who wants to have a go, but I thought I would keep this one to the theory.
Edit: Just to make it clear, I didn't adjust the screws I labelled as X, Y and Z as I didn't want to upset my own camera any more than I needed to to find out what does what. I have, however, tried adjusting everything else and I've no doubt about what they do. There is just a small question still about the actual effect of adjusting screw Y. It may be that there is more to it than I'm thinking. But if anyone else can throw more light on to it, please post it here. But please don't email with comments suggesting it's unsafe for me to be posting this...
I've been informed the pictures associated with this post and the one further down the thread have gone missing. As I seem to have lost the originals, I've retaken the pictures and rewritten the text. It's all posted on my Web site at http://www.z0g.eu/zi/zi_align.htm
_____
Well I couldn't resist doing some further investigation and decided to lift the lid of my ZM to see exactly what screws did what. This is what I found. Some of my conclusions haven't been confirmed as I don't want to make any unecessary adjustments to my ZM but I'm pretty sure what I'm saying here is correct.
In the other thread on this subject it was determined by several people that some adjustment screws could be found under the accessory shoe. I also added that some more screws could be found under the shutter speed selector.
Let's start with the ones under the accessory shoe...
To explain what these do requires some understanding of the rangefinder layout and I've done a couple of diagrams that I hope will help. First the general optical path.
On the far right is a prism which rotates when the focus is adjusted. Next to it is a glass block then some surface mirrors then finally the prisms that combine the images in the viewfinder. This is pretty standard stuff but the main point is that we have a prism that has to be rotated a little as the lens is focussed.
To achieve the linkage between the lens cam follower and the prism there is a series of levers thus...
The lens cam follower moves in and out and causes lever A to swing around point Q. Lever A engages the cam end of lever B and causes lever B to move back and forth also. Lever B is rigidly fixed to lever C which is hinged at P where the prism is mounted.
Now, look more closely at the join between levers B and C.
This is what you can see if you look below the accessory shoe. There are three screws that I've labeled X, Y and Z. X is the black, cross head, locking screw and Y and Z are slotted adjustment screws. In the centre we also have two fixed studs which are located in the curved slot in lever B. The two adjustment screws Y and Z are eccentric screws - that is, their heads are offset. If we unlock the locking screw X and adjust Y, lever B slides back and forth as the eccentric head of Y pushes it. The movement is controlled by the two fixed studs so lever B can only move in a slight arc.
If you look back at the previous image, you will see that moving lever B in this arc will alter the pitch of the edge along which lever A operates. The overall effect of this is that adjusting screw Y will change the amount that the lever B and C assembly moves for a given amount of movement of lever A. (with me so far???)
So what of screw Z? Well this isn't an adjustment screw as such. What it does is to keep lever B in close contact with the two fixed studs. If you look at the following pic you'll see that lever B is held tightly up against these studs so there is no slop in the movement. As far as I can see, that's all screw Z does.
You might also note in this picture the sealant on the locking screw. I think it's also worth noting that any attempt to adjust screw Y without first unlocking the locking screw will probably result in damage (I guess there's some people who didn't want to hear that). Similarly, if screw Z is adjusted you will either introduce slop into the system or you will cause damage by pushing lever B up against the fixed studs.
My conclusion to the above, and this is based also on what follows, is that screw Y is to adjust the close focus of the rangefinder.
So now, moving across to the screw I noted under the shutter speed selector. Here's what it looks like with the shutter speed dial removed.
The prism is located under the metal disk that can be seen near the screw. If you look either side of the black crosshead screw you can see two slots which is the slot of the adjustment screw. The crosshead fits down the centre of the adjustment screw and locks it. If the locking screw is loosened, and the adjustment screw turned, the prism will rotate slightly in it's mount. The adjustment screw is another eccentric type and rotating it moves the prism mount slightly. The effect of this is easy to understand and it will adjust the horizontal alignment of the rangefinder image.
Here's another pic of the arrangement with the camera cover off so it can be seen more clearly.
Also note the glass block next to the prism. We'll deal with that in a minute.
So, what we have are two adjustments of the horizontal alignment. My conclusion is that the first one, that can be found under the accessory shoe, is, as I said, the close focus adjustment while the one next to the prism is the infinity adjustment. I have spent some time pondering this as, at first, I wasn't sure which was which but I finally decided it was this way around when I thought of them as being a Gain and Zero control (something more familiar to the electronic guys amonst you of which I'm one). The adjustment under the accessory shoe effects the degree of movement of the prism for a certain amount of movement of the lens cam follower. I interpret this as a gain adjustment. The movement of the prism will have equal effect over the full range of movement so this is more like a zero of offset control. The question then is, at what point of the range do you adjust the zero control. In this case, I'm guessing that the arc through which lever B moves when screw Y is adjusted is centred on or about the position where lever A will contact lever B when the lens is on infinity. This is the only fixed or known point so it would make sense. If this is so, then adjustment of screw Y when the lens is set to infinity would have no effect so this must be the control for close focus and adjusting the prism is for infinity adjustment. Those people who have tried adjusting the screws under the accessory shoe and noted horizontal movement of the rangefinder image may disagree with this but, unless the locking screw was loosened before making the adjustment, the resultant effect is unpredictable as it would probably result from distortion or damage of lever B.
So how about vertical adjustment.
Look at this picture of the way the prism is mounted. Note especially the two strips of metal below it.
The lower of these two strips is the end of lever C. The prism is actually mounted on the upper strip of metal and, between the two, where I've put the red circle, is a small adjustment which moves the upper strip up and down. Although it's difficult to see in the picture, this adjustment has a pair of flats on it so it can be rotated and it also has sealant on it to lock it in position. This is obviously an adjustment and it alters the vertical alignment of the rangefinder image. The thing to note here is that this is not accessible without removing the top cover - but read on...
In the picture here you can see again the prism and the glass block next to it. In front of the glass block is an adjustment screw. This is another eccentric screw sitting in a slot.
The holder of the glass block is pivoted on the pivot that can be seen next to the screw. The effect of rotating the screw is to tilt the glass block on this pivot. Now this will effect the vertical alignment of the rangefinder image but it is quite a crude adjustment and I'm guessing this is not intended to be moved once assembled. I assume this because the mechanism has been very firmly sealed by the gunge that can be seen across the top of the mechanism above the screw. This gunge is set hard and there's no way of removing it easily. However, I did try turning the screw and, even with everything sealed up, I did get some vertical movement of the rangefinder image. This screw is accessible without removing the top plate, though it's difficult to get at, but it is a possible solution to vertical alignment problems. But an altogether, possibly, easier way to adjust the vertical alignment is to bend (yep I said bend) the end of lever C up or down. This end of lever C with the prism mounted on it is not supported at all by the body of the camera, it's only attached to the rangefinder assembly, so it will flex up and down a little. I found just by putting a little pressure on it either up or down, I could make small adjustments to the vertical alignment. It should be possible, I think, to do this via the shutter speed selector hole in the top plate so, as long as any error is small, this may be a quick and dirty solution.
So, that's pretty much it. I'm going to do another post with some more practical details of how to get at and do these adjustments for anyone who wants to have a go, but I thought I would keep this one to the theory.
Edit: Just to make it clear, I didn't adjust the screws I labelled as X, Y and Z as I didn't want to upset my own camera any more than I needed to to find out what does what. I have, however, tried adjusting everything else and I've no doubt about what they do. There is just a small question still about the actual effect of adjusting screw Y. It may be that there is more to it than I'm thinking. But if anyone else can throw more light on to it, please post it here. But please don't email with comments suggesting it's unsafe for me to be posting this...
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