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Didden
Tinkerer
Username: Didden
Post Number: 3
Registered: 08-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 04, 2010 - 09:42 am: | 
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Have a nice Yashica EM and took out today and found the focus is off. If I am focusing to infinity it goes into focus before it the camera actually gets there. If I am trying to focus a short distance it doesn't seem to even focus that in. The board that goes in and out has probably just over a 1/16" gap at the bottom when the top is flush. Hope this all makes since.
Thanks
Dennis |
Markus
Tinkerer
Username: Markus
Post Number: 140
Registered: 08-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 05, 2010 - 10:51 am: |
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It might be that the mechanism that the lens board is attached to has been bent by some sort of impact, perhaps when the camera was dropped. To rectify this, you need to remove the leatherette from the front and remove the lens board. Then you can shim it so that the lens board is once again parallel to the film plane. Then you need to adjust the focus knob so that infinity is correct. To do that, use the method described in the articles section of this web site. |
Will_inoue
Tinkerer
Username: Will_inoue
Post Number: 31
Registered: 06-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 05, 2010 - 01:52 pm: |
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Are you saying the camera lensboard bottoms out before the focus knob reads infinity? It may be something as simple as resetting the focus knob. Remove the pin face screw/cover (careful it's bakelite) at the center of focus knob, and loosen nut inside with nut driver - then reset focus. To do this you will need to put a ground glass at the film plane and check the camera is focused at infinity. If the viewing lens (upper one) does not coincide at this point you will need to adjust that by removing front lens plate and loosening set screw on side of lens. Then rotate viewing lens until they match. |
Didden
Tinkerer
Username: Didden
Post Number: 4
Registered: 08-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 06, 2010 - 02:30 pm: |
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The lens board is not parallel and when set at infinity the board at the bottom is still out about 1/16" or little more. I think I need to do as Markus said and get the board trued up. Takes great pictures is I can get this adjusted correctly.
Thanks will try to get on this and report back in a few days.
Dennis |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 1108
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Monday, September 06, 2010 - 05:42 pm: |
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Sounds like it's had a bashing. You can adjust the viewing lens and/or the focusing screen to match the focus between the viewing and taking systems, but it is critical that the lenses be parallel to the film plane or all else is futile. |
Didden
Tinkerer
Username: Didden
Post Number: 5
Registered: 08-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 09, 2010 - 08:44 pm: |
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The camera really does not look like it has been dropped or damaged. I have taken the front apart and the rails both bottom hole are out farther than the top but they are equal top and bottom. Meaning they are equal on the top back just a little and both out more than top out on bottom. I am only guessing that these would need to be shimmed to make this equal top and bottom and make the lens equal top and bottom. I can do this but focus is still off does the focus lens need adjusted? If so how might this be done?
Thanks |
Mareklew
Tinkerer
Username: Mareklew
Post Number: 178
Registered: 03-2010
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 10, 2010 - 08:59 am: |
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Didden, there are few things that we need to clear up first here, before you attempt to fix anything.
First a little about what's inside this camera:
1. The focusing knob rotates a simple axle that goes across the whole camera.
2. On this axle there are two eccentric assemblies, one left and one right. These are fixed to the axle and not adjustable.
3. The rails, to which the front lens panel is mounted, are made of two separate pieces of metal. One for left top and left bottom mounting point, and one for right top and right bottom. Each side has a hole in the middle, in which the eccentric parts sit.
4. When you rotate the focusing knob, the eccentric elements either push both rails out front, or pull them back in. The rails are NOT interconnected at any point, except being screwed to the lensboard.
5. To make sure the lensboard is parallel to film, the focusing rails move in guides fixed to the camera body cast.
Now, I find it unlikely, that the rails got bent, leaving no mark on the camera. These beasts are STURDY. I dropped a Yashica front down on cobblestones once, I had bent the corner of the lensplate, wasted the front panel cover, but the focusing stayed true. I didn't believe it at all and ended stripping the camera down to pieces and rebuilding it again only to find that really, the rails WERE straight.
If you followed me this far, You will not be surprised, that I want to first figure out *IF* there's something wrong with your focusing rails before trying to fix them.
Okay, but now let's get on:
Every mechanical device has manufacturing tolerances, and so either the machining has to be done to tolerances tight enough, or there's some way to adjust things. Rule of thumb: optics require too tight tolerances to be made non-adjustable. Especially true for cameras 50+ yrs old.
The axle, eccenters and focusing rails are not adjustable. The taking lens is screwed hard into the lensboard and is not adjustable either. After the camera was put together, before attaching the lensboard, the focusing rail montpoints were ground to match distance from the film plane at each corner. This distance you have to check now. It is not trivial, but with digital calipers you can get quite far.
Assuming the mountpoints are straight, the lensboard is parallel to film. Next adjustment is getting the infinity stop right. It is adjusted by movng the focusing knob relative to the axle - this is the only adjustment available.
Since the viewing lens and ground screen also have tolerances, the next adjustment point is the viewing lens. It is fixed by a small lock screw and can be screwed n and out. Adjust the focus for film plane to some target distance (NOT by relying on the scale or on infinity stop!!!! You have to actually focus on the film plane using i.e. ground glass) and make sure that this target appears sharp on ground glass too.
Marek |
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