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09-05-2016, 11:42 PM   #1
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Help with using a auto-takumar lens on a Spotmatic F

Greetings all. I just joined the forum and had a question about using an..... auto-takumar 1:2.3 / 3.5 with a Pentax Spotmatic
I wanted some tips on
1.how to test the lens is working properly.
2.how use this lens with my spotmatic f and how it works.
Thanks

09-05-2016, 11:50 PM   #2
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Help with using a Auto-takumar 1:2.3 / 3.5

I just got hold of this lens and have not used an auto-takumar before and wanted some tips on how this lens works. I had read somewhere it is semi automatic
I will be using it with my Spotmatic F and any tips on how to get the best out of it would be helpful
Also any tips on checking if it is working properly
Many thanks
09-06-2016, 12:12 AM   #3
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The SP F was the last development of the fully manual SP. What made it different beside the larger battery, was that it metered with the lens wide open. The later SMC lenses had a small button that helped lock them into the auto made (only when on the SPF). The lens communicated the actual aperture set, and the light meter calculated the difference.
The original Auto Tacumar was only 'auto' in that it could be automatically tripped into a pre-set aperture. If you use it on the SPF, make sure to cock it fully open to meter for the corresponding speed. I don't think this lens communicates its aperture to the camera, so you may have to adjust the speed you metered for wide open, to compensate different apertures.
09-06-2016, 12:18 AM   #4
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Welcome to the Pentax Forums!!

There is a lens database entry for your Auto-Tak:

Auto Takumar 35mm F2.3 Reviews - M42 Screwmount Wide-Angle Primes - Pentax Lens Reviews & Lens Database

The aperture mechanism is semi-automatic, meaning that it will stop down for exposure automatically, but requires the lever on the side to reopen the lens aperture for focus. I don't have specific experience with this type of lens on the Spotmatic F and can only imagine what process might work best for metering and normal shooting with that camera. With any luck other Auto-Tak owners will offer their wisdom.


Steve

09-06-2016, 06:50 AM   #5
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QuoteOriginally posted by arnold Quote
If you use it on the SPF, make sure to cock it fully open to meter for the corresponding speed. I don't think this lens communicates its aperture to the camera, so you may have to adjust the speed you metered for wide open, to compensate different apertures.
I think you have gotten the metering step backwards.

The Auto-Tak 35/2.3 predates metered bodies and like most M42 lenses has no linkage to communicate aperture to the camera. I was not going to speculate on usage with the SP F (I own neither camera nor lens), but would suggest that stop-down metering/shooting sequence would be similar to other non-S-M-C/SMC Taks and might go something like this:
  1. Confirm lens aperture is in "ready" state (switched to wide open)
  2. Focus on subject
  3. Slide the meter switch to "on" position. This will activate the meter circuit as well as trigger the stop-down mechanism on the lens. Lens will stop down.
  4. Adjust aperture/shutter to center the meter needle
  5. Press shutter release to make the exposure
  6. Reset aperture and advance film to be ready for the next shot
  7. Repeat all but steps #3 and #4 until either light or subject changes
The above steps are similar to that given in the English version of the SP F manual available on the Butkus site:

http://www.butkus.org/chinon/pentax/pentax_spotmatic_f/pentax_spotmatic_f.htm


Steve

Last edited by stevebrot; 09-06-2016 at 07:57 AM.
09-06-2016, 03:20 PM   #6
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QuoteOriginally posted by stevebrot Quote
I think you have gotten the metering step backwards.

The Auto-Tak 35/2.3 predates metered bodies and like most M42 lenses has no linkage to communicate aperture to the camera. I was not going to speculate on usage with the SP F (I own neither camera nor lens), but would suggest that stop-down metering/shooting sequence would be similar to other non-S-M-C/SMC Taks and might go something like this:
  1. Confirm lens aperture is in "ready" state (switched to wide open)
  2. Focus on subject
  3. Slide the meter switch to "on" position. This will activate the meter circuit as well as trigger the stop-down mechanism on the lens. Lens will stop down.
  4. Adjust aperture/shutter to center the meter needle
  5. Press shutter release to make the exposure
  6. Reset aperture and advance film to be ready for the next shot
  7. Repeat all but steps #3 and #4 until either light or subject changes
The above steps are similar to that given in the English version of the SP F manual available on the Butkus site:

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


Steve
I am not sure about this, Your suggestion is stop-down metering, which is fine for the SP, but the SPF is designed for open metering with a lens that communicates aperture. My auto Tacumar has nothing on the back but a stop-down trip button, The camera won't know the lens has closed. Am I missing something here?
edit: I am working on the assumption that the SPF will not meter accurately at closed apertures. Hence my suggestion to meter wide and calculate the different adjustment to speed. I would have to try it out to confirm this though.

Last edited by arnold; 09-06-2016 at 03:42 PM.
09-06-2016, 03:32 PM   #7
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QuoteOriginally posted by arnold Quote
I am not sure about this, Your suggestion is stop-down metering, which is fine for the SP, but the SPF is designed for open metering with a lens that communicates aperture. My auto Tacumar has nothing on the back but a stop-down trip button, The camera won't know the lens has closed. Am I missing something here?
Perhaps

While the OP's lens has the feature, not all Auto-Taks are semi-automatic. Some of the later variants have fully automatic diaphragms as found in the Super-Taks. A good summary may be found on the lens database page for the screw mount 55/1.8 Takumars.

https://www.pentaxforums.com/lensreviews/SMC-S-M-C-Super-Auto-Takumar-55mm-F1.8.html

As for the SP F...Yes, it does support open-aperture metering, but only with S-M-C/SMC Takumars (most) and a few transitional ST lenses. With other M42 lenses, legacy stop-down metering is available via the stop-down/meter switch on the left side of the lens mount. When a legacy lens is mounted the switch works the same as on earlier model Spotmatics. This is covered on p21 of the user manual and calls out the Auto-Takumar series explicitly for this technique. The camera does not need to know if the lens is stopped down. If the stop-down meter switch is in the up position, the actuator/"flipper" in the mount opening will engage the pin on the lens to stop down the lens. The camera will meter based on the light reading at the sensor modified by the bias applied by the aperture simulator (in this case, none) .


Steve

Last edited by stevebrot; 09-06-2016 at 03:58 PM.
09-06-2016, 03:49 PM   #8
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QuoteOriginally posted by stevebrot Quote
Perhaps

While the OP's lens has the feature, not all Auto-Taks are semi-automatic. Some of the later variants have fully automatic diaphragms as found in the Super-Taks. A good summary may be found on the lens database page for the screw mount 55/1.8 Takumars.

SMC/S-M-C/Super-/Auto-/Takumar 55mm F1.8 Reviews - M42 Screwmount Normal Primes - Pentax Lens Reviews & Lens Database

As for the SP F...Yes, it does support open-aperture metering, but only with S-M-C/SMC Takumars (most) and a few transitional ST lenses. With other M42 lenses, legacy stop-down metering is available via the stop-down/meter switch on the left side of the lens mount. When a legacy lens is mounted the switch works the same as on earlier model Spotmatics. This is covered on p21 of the user manual and calls out the Auto-Takumar series explicitly for this technique. The camera does not need to know if the lens is stopped down. That is assumed because the stopdown/meter switch is in the up position (operates the actuator "flipper" at the mount opening).


Steve
OK, then it seems that it is only with the later lenses that one must not meter stopped down. That it is OK if the camera is not confused by information form the lens, as would be the case from later lenses. Still, I wonder if my method would be more accurate even if a bit more complicated.

09-06-2016, 04:29 PM   #9
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QuoteOriginally posted by arnold Quote
OK, then it seems that it is only with the later lenses that one must not meter stopped down. That it is OK if the camera is not confused by information form the lens, as would be the case from later lenses. Still, I wonder if my method would be more accurate even if a bit more complicated.
I don't have a SP F or similar body on my shelf, but I do have an S-M-C lens in front of me. It differs from the common auto-aperture M42 in that it has an aperture simulator "follower" coupling similar to that found on all but the most recent K-mount lenses and a metal boss that might serve to turn on the primary (wide open) meter circuit. The boss engages a block at the base of the prism housing. It is my suspicion that the meter is probably off by default unless that boss is present.

As for accuracy, I would not expect there to be any particular difference (both measure light within the meter's linear range), though the range of valid EV for the meter may be somewhat wider at the low end with the open-aperture system. This much I do know, the two methods are calibrated differently using a specialized test IC.


Steve

Last edited by stevebrot; 09-06-2016 at 04:35 PM.
09-06-2016, 10:53 PM   #10
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Thanks for all the advice. Still a bit confused but I guess eventually I will get my head around it
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