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10-13-2011, 12:51 AM   #1
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Help: SF1/SFX: aperture lever control problem

My beloved SFX started behaving oddly: any A/F/FA lens engaged in the A setting produces underexposed pictures, because the body identifies the lens (7 different types tested!) correctly and sets program line and exposure correctly according to the metering and the lens attached. But if the shutte is fired, the lens diaphragm is stopped down to the smallest aperture thus resulting in severely underexposed pictures.

This does not happen when a lens is K/M or the A setting not engaged, because the diaphragm lever of the lens takes care of the diaphragm aperture value once the shutter is fired. The diaphragm lever on the camera moves correctly all way up in any case. The lenses are ok, too. Everything works perfect until you engage the lens into A setting...

Conclusion: the culprit must be the mechanism that stops the aperture lever at the correct aperture position when you trip the shutter (controlled by the camera when A setting is engaged (!), the lens lever position in A is identical with the smallest aperture of the lens in non-A).

My question is: Is this mechanism a tiny motor? Or a magnet? Or a mechanical spring-type mechanism? Is it different in A Super A MF body in comparison to the SF1/SFX?

Later cameras (MZ series and presumably Z series) had a depth-of-field preview button that was using a tiny motor to stop down the lens for a short moment and these motors are notorious for breaking in the ZM series.

But is there a mototr in the SFX, because they do not feature a DOF preview function? And the Super A can't have a motor anyway, powered only by two button cells...

Any help is highly appreciated, because it would give me an idea whether there's do-it-yourself tinkering possible or repairing makes any sense!

10-13-2011, 08:36 AM   #2
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There are two things that could go wrong: the electronics and the mechanical parts (spring and gears with electrical contacts) which control the aperture lever. You need right kind of tools to open the camera: JIS type screw drivers (00 and 000) and a soldering iron to heat the screw. I think it would be much simpler to get another SF1 which works. I have SF1 and SF10 I want to throw into recycle bin. I only use MZ-5N and MZ-6. These third generation AF cameras are smaller, lighter, and much more versatile.

Last edited by violini; 10-13-2011 at 11:57 AM.
10-27-2011, 06:28 AM   #3
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Sorry to bump this one up, but has no one info about the technique used in Super A and SF1 to control the aperture in A mode?

Let's say not for repair but for general knowledge...

And yes, I have MZ-5n and MZ-7, but I much prefer the SFX(n) - it's a different build quality...
10-31-2011, 05:51 PM - 1 Like   #4
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I have two SF10's which I bought for the lenses. Since the camera body has no re-sale value, I dissemble one just to see how it operates. The camera has two magnesium alloy frames as shown in the photo; the one on the left is film transport and shutter block; on the right is mirror box. There is no mirror motor. The camera uses two solenoids to operate the mirror and the aperture (on top and bottom of gear box). One could call the bottom one (green color) a linear motor because it push/pulls a center steel rod in and out. It has relatively large focusing motor (bottom left corner). On top of the prism, there is a tiny lens which concentrates light on a photo cell for metering. This is a first generation auto camera, I think its design is rudimentary. The eye-piece of viewfinder is single element thick plastic lens. The construction of MZ-5N is much more advanced. People criticize Sony for using fixed mirror, in fact, all the mirrors in auto focus cameras are half silvered to allow some light to transmit through and then reflects to the CCD sensor for focusing. This is the reason that viewfinders in manual focusing cameras are brighter owing to fully silvered mirrors. The construction of the shutter is rather simple. Two coil springs and two solenoids operate a few thin metal blades. The blade traveling time must be much shorter than the shortest shutter time, otherwise the exposure would not be uniform across the frame. In cameras such as PZ-1 which have 1/8,000 sec., the springs would be very strong to flip the metal blades even faster, but probably would create unwanted vibration in the camera. The uncrippled lens mount has a lever which goes inside the lens to couple with the aperture ring. This lever has 9 contact points corresponding to the common 9 settings on the aperture ring.

Vranx, I would guess that in your case the top solenoid (gray color) is not working, resulting in aperture control lever slides all the way to the end and thus the smallest aperture under A setting.


Last edited by violini; 12-18-2011 at 02:03 PM.
11-02-2011, 09:33 AM   #5
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QuoteOriginally posted by violini Quote
The blade traveling time must be much shorter than the shortest shutter time, otherwise the exposure would not be uniform across the frame.
A common misconception. On fast shutter speeds the second curtain starts travelling before the first one is done, so only a slit moves over the film. As long as they move at the same speed, the exposure is even. It only needs to be fully open for (non HSS) flash to work.
11-02-2011, 04:11 PM   #6
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Yes, I know that, but the blade speed is controlled by the spring while the shutter time by electronics. After some 30 years, I would expect the spring to suffer some amount of fatigue. In MZ-6, the flash synchronization in p-TTL can reach 1/4000 sec., the shortest shutter time. This is the reason we don't use the term "shutter speed", but shutter time or exposure time.

Last edited by violini; 11-02-2011 at 04:50 PM.
11-03-2011, 03:28 AM   #7
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That's HSS flash, the shutter is not fully open. It could take a second to perform this 1/4000 exposure, it would still work. (With some blurring from diffraction in the shutter slit, I suppose.) So this is unrelated to how fast the shutter moves.

It's possible you mean the same thing as me, but the text you write very much gives the impression that you believe the shutter must move faster for shorter shutter times.
11-05-2011, 02:49 PM   #8
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QuoteOriginally posted by violini Quote
I have two SF10's which I bought for the lenses. Since the camera body has no re-sale value, I dissemble one just to see how it operates.
Inquiring minds want to know... that's really cool and kind, thanks for your effort!!! Yes, solenoids make sense, especially the Super A (and others) with tiny body and tiny battery power wouldn't have done well with a motorized solution... The SF series were big and heavy enough already, I imagine, so they redesigned the with the Z (?) or at least the MZ series.

I'm not ready to tear her apart, because all the rest is working, maybe I'll practise for the show with the broken A3 laying around...

But that's why I like this forum: cameras are opened to answer questions - that's cool!

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