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07-19-2013, 10:06 PM   #1
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Manual/Auto Nightmare

Greetings and I hope everyone is well.

Okay here is my dilemma. I have an Asahi Spotmatic F camera and two lenses with M42 screw mounts. One lens is a prime 55mm 1:2 Takumar, and the other is a 135mm 3.5 Takumar. Both are SMC and in very good shape. I placed the 135mm on the camera and in very bright daylight, I had problems with the meter. Meaning, I could not get the needle centered. It always showed overexposed. Without boring everybody with a lot of details, I changed the lenses to Auto instead of Manual and everything went fine. Why? Obviously the SP-F has nothing automatic about it. A very old release from Asahi. My next thought was, okay this is an old camera that has a maximum shutter speed of 1/1000 using a slow telephoto lens and ISO 800 speed film on a very bright day. I switched over to ISO 400 speed and had the same problems until I changed both lenses to Auto mode. I switched back to ISO 800 and everything was fine with lenses on Auto.

Thanks for any assistance.

Tony

07-19-2013, 11:07 PM   #2
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You might get more traction on the film SLR section of this site. It sounds like you are experiencing one of the quirks of using the Spotmatic F. You might want to ask the mods to move this post.

In the mean time, the camera manual might be a good thing to read. There are fine points to using SMC/S-M-C lenses for open-aperture metering. You can download it for free from the Butkus site (donations accepted):

Asahi Pentax Spotmatic F instruction manual, user manual, free PDF manual, camera manual

Oh...and one more thing. The "auto" setting on your lens has nothing to do with exposure automation. In this case auto refers to automatic as opposed to manual aperture. When the iris diaphragm is in automatic mode it closes down "automatically" at exposure time and reopens afterwards. In manual mode the aperture is stopped down to the setting on the ring.

BTW...don't slide the lens manual/auto switch on your SMC lenses when they are not mounted to the camera. It will not move unless mounted or a rear cap is fitted. Forcing it will damage the mechanism.

Steve

Last edited by stevebrot; 07-19-2013 at 11:17 PM.
07-19-2013, 11:30 PM   #3
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QuoteOriginally posted by stevebrot Quote
You might get more traction on the film SLR section of this site. It sounds like you are experiencing one of the quirks of using the Spotmatic F. You might want to ask the mods to move this post.

In the mean time, the camera manual might be a good thing to read. There are fine points to using SMC/S-M-C lenses for open-aperture metering. You can download it for free from the Butkus site (donations accepted):

Asahi Pentax Spotmatic F instruction manual, user manual, free PDF manual, camera manual

Oh...and one more thing. The "auto" setting on your lens has nothing to do with exposure automation. In this case auto refers to automatic as opposed to manual aperture. When the iris diaphragm is in automatic mode it closes down "automatically" at exposure time and reopens afterwards. In manual mode the aperture is stopped down to the setting on the ring.

BTW...don't slide the lens manual/auto switch on your SMC lenses when they are not mounted to the camera. It will not move unless mounted or a rear cap is fitted. Forcing it will damage the mechanism.

Steve
Hi Steve,
Thanks very much for your reply. The 55mm Takumar can only be adjusted by pressing in on a very tiny button under the threads. Once mounted on the camera, it cannot be adjusted. The 135mm Takumar can be adjusted with no problems while it is mounted. I thought I was on the right forum: Pentax SLR Lens Discussion. Thanks again for your help. You are correct, there are many quirks with the Spotmatic F, however it is a very reliable and solidly built camera.

Regards,

Tony
07-20-2013, 08:41 AM   #4
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If the lens stops down when you press the pin in the mount off camera, the lens will stop down properly mounted on the camera, provided the camera's stop down plate is working properly. You can test it by opening the back of the camera and watching with the lens mounted and the lens cap off. Set the shutter speed to bulb (past 1" on the dial) and hold the shutter down while looking through the camera. Try this with wide open and fully stopped down apertures. You will see that the aperture does close properly. The camera operates the pin and stops the lens down.

It might just be that you did not have the advance lever off the rest position when you were checking at ISO 800. To turn the meter on, you need to pull the advance lever slightly away from the body of the camera.

07-20-2013, 01:16 PM   #5
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QuoteOriginally posted by Tonytee Quote
Hi Steve,
Thanks very much for your reply. The 55mm Takumar can only be adjusted by pressing in on a very tiny button under the threads. Once mounted on the camera, it cannot be adjusted. The 135mm Takumar can be adjusted with no problems while it is mounted. I thought I was on the right forum: Pentax SLR Lens Discussion. Thanks again for your help. You are correct, there are many quirks with the Spotmatic F, however it is a very reliable and solidly built camera.

Regards,

Tony
There are just more people in the film area who have used a Spotmatic F. That camera body can interact with screw mount lenses, unlike the digital SLRs most of us are using. The camera manual explains it better, but basically any lens with that tiny button was meant to work with the Spotmatic F in the lens's Auto mode. There's a groove machined in the lens mount just to allow that tiny button to pop out. The camera can figure out where you have set the aperture ring without stopping the lens down at all. It was leading edge tech for the M42 system, with some compatibility issues for the lenses without a button.
07-20-2013, 01:52 PM   #6
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QuoteOriginally posted by Canada_Rockies Quote
If the lens stops down when you press the pin in the mount off camera, the lens will stop down properly mounted on the camera, provided the camera's stop down plate is working properly. You can test it by opening the back of the camera and watching with the lens mounted and the lens cap off. Set the shutter speed to bulb (past 1" on the dial) and hold the shutter down while looking through the camera. Try this with wide open and fully stopped down apertures. You will see that the aperture does close properly. The camera operates the pin and stops the lens down.

It might just be that you did not have the advance lever off the rest position when you were checking at ISO 800. To turn the meter on, you need to pull the advance lever slightly away from the body of the camera.
Well sir, I thank you very much for your input. One point, and that is according to manual, the only way to activate the light meter is to remove the lens cap. I find this to be true. Also, according to the manual, any lens used on the SP-F, must be left on Auto. Again, thank you very much for your assistance. I will certainly do as you have suggested. I will keep posting on my progress.

Ciao,
Tony
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