Yashica Mat-124 not focusing correctly, hoping for some repair advice

[himself]

Hi everyone,

I recently bought a Yashica Mat-124 and while it wasn't pristine it did work as it should, however recently I've been having problems with focusing - that is to say it won't focus correctly.

Basically, the camera will focus but the gg doesn't match the focus scale; for instance an object at infinity measures about 4m on the focus scale. For the moment my assumption is that gg has become misaligned after a knock (I travel a lot, so it get's a little bit of a beating at airports and on buses & trains) because the focus isn't even across the surface of the gg, that's not say that it's focused in the centre but soft at the corners, but rather focused at the top and not at the bottom.

So before I start taking it apart and playing with it, I was hoping someone has had similar problems and knows what might be the problem and can offer some advice.

Thanks in advance!
Dafydd

 

[BMbikerider]

The focussing screen can be removed quite easily after the focussing hood is rmoved. It may be that the screen has been taken off before and not replaced correctly which will account for the difference in focussing top to bottom. You may find if you take the screen out there is some sort of detritus stopping the screen from lying flat. Be careful with the screen when you take it off - they are delicate.

It may also be that the mirror has been removed before as well and that may be the same problem. Only by opening up the screen to get to the mirror will you see what the problem may be. Similarly to the screen be careful how you handle the mirror should you have to remove it. Like the mirror they are delicate and finger marks could be difficult to remove.

 

[himself]

The focussing screen can be removed quite easily after the focussing hood is rmoved. It may be that the screen has been taken off before and not replaced correctly which will account for the difference in focussing top to bottom.

Thanks.

I took the hood off and checked the screen, but both the gg and fresnel are the right way up and in the right order, I didn't think to check the mirror though, so I'll give that a check too later.

I've also done a couple of further tests, and from what I can tell the problem only seems to be from after 3 meters. Near focus is accurate, or at least within a small enough margin that's acceptable.

 

[shutterfinger]

There are some assembly diagrams for download at https://www.manualagent.com/yashica/mat-124g/repair-manual
Is the front/lens standard square to the body? Do the negatives match the focus error on the focus screen?

 

[nosmok]

I had a beat up Yashica-mat that actually had the front standard (dual-lens focusing thingy, whatever) out of parallel when I got it. I cranked it all the way back in, gave it a little push on the further-out side, it snapped into place and was perfectly fine after that. Just another thing to check, easy to see if you're looking for it.

 

[zanxion72]

If I were you I would adjust the scale on the focusing knob. The ground glass and the mirror are hard to be knocked off position on the 124G. My guess is that the focusing scale on the focusing knob is out, and this could be easily done by applying too much force past the stop.

Here is some additional help on fiddling with the knob:
http://www.rangefinderforum.com/classics/forum/messages/2/19499.html?1280962001

 

[BMbikerider]

If I were you I would adjust the scale on the focusing knob. The ground glass and the mirror are hard to be knocked off position on the 124G. My guess is that the focusing scale on the focusing knob is out, and this could be easily done by applying too much force past the stop.

Here is some additional help on fiddling with the knob:
http://www.rangefinderforum.com/classics/forum/messages/2/19499.html?1280962001

It seems you have missed the point that the focussing is 'out' on one part of the screen but not on another, which points towards either the screen being out of true (eliminated) or the mirror out of place, which has not been checked. If it was the focussing knob out of adjustment, all the image would be out of focus.

 

[zanxion72]

It seems you have missed the point that the focussing is 'out' on one part of the screen but not on another, which points towards either the screen being out of true (eliminated) or the mirror out of place, which has not been checked. If it was the focussing knob out of adjustment, all the image would be out of focus.

Indeed, I've missed that. Most likely that the mirror has been clumsy "repaired" after it came off once (uneven layer of glue).

 

[himself]

mornin' all,

thanks for the tips!

I'll go through them all this morning and see if any are obviously the cause.
I had thought it may be because the knob had been - either taken off and put back on incorrectly, or over turned - but the close focus is accurate, so for now I think I'll concentrate on the mirror being misset and front standard not being quite right.

As far as I can see (by eye), the front standard looks to be parallel with the body. But I'll measure it more accurately just to be sure.

Oh, and unfortunately the problem has appeared half way through a roll of film, so I'm not sure if gg matches film yet.
It looks like I'll just have to go through it for now and compare.

thanks again!

 

[himself]

quick update!

Just took the hood off and it's sorted now.
The bottom of the mirror wasn't sat correctly in it's bed, which was throwing off the focus on the gg. I took it out and reset it correctly and now focus is even across the gg and matches focus scale.

Thanks for the help!

It's funny how something that seems so obvious only becomes so after someone else has pointed it out to you