Compared to the Minox, the Yashica atoron is easy to open and maintain. The shutter mechanism in particular is very easy to clean if the shutter opens too slowly or not at all. Problems with the shutter blades – the major weakness of the Minox – are not really to be expected. This is because they are very robust and well protected. The selenium cell of the light meter is easy to replace; the problem is rather where to get a replacement cell.
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Open the housing
There are no screws or other instructions on the housing of the atoron on how to open the camera. However, there are detailed instructions online here, which I followed. Many thanks to ic-racer, without whom I would not have made it. I have documented my own work in detail with pictures so that you can see how it works.
First I unscrewed the film advance lever. You pull it out, but not completely. You can hear it click into place at short intervals. When it clicks into place for the last time, you stop pulling. In this way, the lever remains in this position:
Now you can loosen the two slotted screws. Be careful, a spring plate on the back of the lever will also come free and fall down.
I secured the end of the lever with a piece of wire so that I could pull it out of the housing if necessary. I then pull the lever as far as it will go and let it slide back into the housing.
Next I removed the dials for the frame counter and the light meter. This requires a tool for two-hole screws. I used a divider for this.
Next, I loosened the two-hole nut at the lower end:
The dial for the frame counter consists only of the screw and the wheel. However, four individual parts are hidden under the exposure setting wheel:
There is a two-hole nut on the top of the camera with which the flash can be screwed on. We also have the back cover lock knob next to it. This is the most difficult to loosen.
There is a tiny slotted brass nut under the black cover in the middle of the knob. To loosen this, I made a suitable tool from a 3 mm wide slotted screwdriver. I milled a U-shape in the middle of the blade. But even with this tool, it was not easy to loosen the nut because it was stuck. In the end it worked with patience and dosed force.
Note the small brass threaded pin in the housing. The brass nut was previously screwed on there.
The housing can only be removed when the back cover is removed first. To do this, turn the back cover lock knob in the “pull” direction and hold until the cover is completely pulled out:
Now you can carefully pull the camera body out of the side of the housing. For me, it worked best when I first swung out the top part. This requires a little force, but be careful, if the housing gets stuck somewhere, you have to remove the cause first. It is recommended – as shown in the picture – to fix the shutter button in the pulled-out position with adhesive tape, otherwise it will get caught in the camera body when pulled out.
Finally, you can remove the front cover. This is necessary if you want to clean the yellow filter, the lens or the viewfinder. Or if you want to replace the selenium cell. The front corver is attached to the camera body at the ends with three slotted screws:
Now you can remove the cover. The camera then looks like this on the inside:
On the inside of the front cover you can see the yellow filter with the corresponding mechanism. To clean the filter, loosen the two screws and then remove the holder and filter. It is also advisable to clean the inside of the viewfinder glass.
Exposure control
EV-Dial
Hebel a dient zur Verschlusssteuerung EV 8.5 bis EV 16 (blaue Pfeile)
Hebel b schaltet “B” ein (rote Pfeile)
Shutter control
Stellung a bei EV 8.5, EV 16?
Shutter
The shutter of the yashica atoron consists of two blades each in form of a triangle. When the lens is closed, both are on top of each other and therefore do not let any light through. When the shutter is released, one blade moves to the left and the other to the right, revealing a diamond-shaped opening in the lens.
The pictures on the left illustrate how the shutter of the atoron is constructed in principle.
The blades 2 and 3 are located between the elements of lens 1. When looking at the camera from the outside, blade 2 is located directly in front of blade 3.
“A” shows the position of the blades when the shutter is closed. The lens is completely covered by both blades.
“B”: When the shutter is released, the blades are pulled apart. Their triangular openings reveal a diamond-shaped part of the lens. As soon as the end position of the blades is reached, the movement is immediately reversed and the blades return to their original position. The lens is closed again.
Such a movement can be generated with the help of a push crank. It turns a circular movement into an oscillating one. Changing the diameter of the circle changes the length of the stroke.
The rotary movement would then come from the sprocket 2 driven by the torsion spring.
This is what the situation “B” looks like in reality:
At the end of the exposure time, the blades move back over each other and close the lens. Here is a video showing this process in slow motion with the aperture fully open:
The light values determined by the light meter are simply mapped in the atoron by limiting the travel of both blades. At a light value of 16, the blades are only moved apart far enough to create a small opening that corresponds to aperture 16. Once this point is reached, the blades immediately move back again. The time required for the blades to move back and forth is 1/250 s. At a light value of 8.5, the blades move as far apart as possible and open the lens corresponding to an aperture of 2.8. The closing process begins immediately afterwards. This process takes 1/45 s.
? It is interesting to note that the blades are always driven at the same constant speed regardless of the set light value. The duration of the exposure depends only on the length of the path that the blades have to cover. This also makes it clear why on the atoron aperture and shutter speed cannot be selected independently of each other.
Replace selenium cell
Replacing the selenium cell is easy if you have a spare cell. I took a working cell from another atoron. It was sold cheaply because the housing had a lot of damage. But the light meter still worked. To remove, slide the plastic housing of the selenium cell to the left until the two screws are visible.
Then loosen the screws and remove cell and holder.
Cut the wire and solder the new cell to it.
Check whether the needle moves according to the incidence of light. Important: the cell must be screwed on, otherwise the electrical ground connection is missing.
Film advance mechanism
Since the films for the atoron have no perforation, it must be ensured by other means that the distances between the negatives on the film strip are even. It must be taken into account that the film take-up spool has a smaller diameter for the first image than for the following images. This is because the wound film makes the diameter larger.
Let’s take a look at the solution first. If we set the frame counter to “1” and press the film advance lever, the take-up spool rotates by approx. 135°:
If we set the frame counter to “50” and press the film advance lever, the take-up reel rotates only by approx. 110°:
This compensates for the increasing diameter of the take-up spool. This solution is achieved with the atoron in a similar way to the Minox. The nose of the film feed lever is pressed against a cam disk located below the frame counter wheel:
At picture #1 the nose of the film feed lever is on the smallest diameter of the cam disk, at picture #50 it is on the largest.
Depending on its position, the lever limits the stroke of the film advance lever and thus the angle of rotation of the take-up spool.
In the following video you can see what happens when you pull the film advance lever. In order to have a clear field of view, the frame counter disk was removed and its cam disks replaced by a washer. Note how the nose of the film feed lever, which adjusts the film advance, rests against the washer (cam disk). The brass screw in the center is the axle of the take up spool:
The further the nose is pushed outwards from the cam disk, the shorter the rotation of the take-up spool. On the right you can also see how the spring of the shutter is wound.
Clean the escapement
The torsion spring drives the large sprocket. This turns the push crank for moving the blades. To ensure that this movement is not arbitrarily fast, the sprocket also drives the escapement, which forces a defined speed. The escapement prevents the sprocket from rotating at maximum speed. The three-stage spur gear turns a rotating mass in the fastest running stage and thus brakes the sprocket to a constant slower speed:
Note the ruby bearing on the front right. The smallest and fastest of the gears runs in it. Rubies are among the hardest natural materials. The use of a ruby bearing significantly reduces wear and friction, resulting in greater precision of the escapement.
