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06-30-2018, 08:13 AM   #1
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K-1 issue with green button on auto mode of old lenses

I noticed my old m42 Takumar lenses will not set the correct aperture while having the lens switch on "auto" und pressing the green button for metering.
This works with my old K-10D and I was always wondering why it is not working with my K-1, anyone else noticed that? Is this maybe just a setting or ist the K-1 missing something here which the older cameras had?


I just recently tried this with my SMC Takumar 135mm F3.5 using the genuine Pentax m42 to K adapter.

06-30-2018, 08:50 AM   #2
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Do you mean correct exposure rather than aperture? The aperture is set by the ring on the lens, not the camera. Pressing the green button activates stop-down metering and the K-1 should set the appropriate shutter speed. As long as you have "Use Aperture Ring" enabled and "Green button in TAv and M" to TV shift. If you set DOF Preview to Optical activating the DOF preview will turn on the meter and you can adjust the EV bar with shutter speed eDial and the aperture with the ring.

All K-mount bodies lack the auto aperture mechanism for screw mount lenses. The only way a screw mount lens with an Auto/Man switch will stop down when set to "auto" is if the lens was modified to keep the stop-down pin engaged or with a flanged M42 adapter that will press in the pin. The genuine Pentax adapter does not have this flange.
06-30-2018, 09:38 AM   #3
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The flanged adapters make infinity focus not possible, which is why Pentax does not have one.
06-30-2018, 11:48 AM   #4
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QuoteOriginally posted by Snakeisthestuff Quote
I noticed my old m42 Takumar lenses will not set the correct aperture while having the lens switch on "auto" und pressing the green button for metering.
The "auto" on the lens slider refers to automatic aperture actuation (works only with M42 bodies) vs. fully manual aperture. On your K-1, the slider should be in the M/Man position for metering or when making the exposure.


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06-30-2018, 11:57 AM   #5
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QuoteOriginally posted by Snakeisthestuff Quote
This works with my old K-10D
No it doesn't
06-30-2018, 12:06 PM   #6
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QuoteOriginally posted by Snakeisthestuff Quote
I noticed my old m42 Takumar lenses will not set the correct aperture while having the lens switch on "auto" und pressing the green button for metering.
This works with my old K-10D and I was always wondering why it is not working with my K-1, anyone else noticed that? Is this maybe just a setting or ist the K-1 missing something here which the older cameras had?


I just recently tried this with my SMC Takumar 135mm F3.5 using the genuine Pentax m42 to K adapter.
How to use/meter Manual & M42 Lenses on all Pentax DSLRs (K-1, K-3, K-5, K-30, etc) - PentaxForums.com
06-30-2018, 03:10 PM   #7
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QuoteOriginally posted by twilhelm Quote
The flanged adapters make infinity focus not possible, which is why Pentax does not have one.
Only some poorly-made adapters with an extended flange do that. The original Pentax adapter allows infinity focus, but Iím not sure if theyíre still made, or not. Of the rest, itís a bit of a lottery whether they do, but some do, even while they have the registration angle wrong, or are hard to remove. Needless to say, I have a few.
06-30-2018, 03:14 PM   #8
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QuoteOriginally posted by RobA_Oz Quote
Only some poorly-made adapters with an extended flange do that. The original Pentax adapter allows infinity focus, but Iím not sure if theyíre still made, or not. Of the rest, itís a bit of a lottery whether they do, but some do, even while they have the registration angle wrong, or are hard to remove. Needless to say, I have a few.
The Pentax adapter isn't typically considered flanged. The flanged ones all deny infinity focus although some lenses can be adjusted to compensate by changing infinity focus. Mostly those flanged adapters work well with macro work.

06-30-2018, 04:17 PM   #9
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QuoteOriginally posted by twilhelm Quote
The flanged adapters make infinity focus not possible, which is why Pentax does not have one.
This is true for the adapters that have an external flange with a cut-out for lens mount locking pin but I'm speaking of those with an internal flange such as the Kipon adapter:

Kipon Pentax Screw M42 Lens to Pentax K Camera Lens Adapter (with Inner Ring) KP-LA-PXK-PXS
06-30-2018, 04:22 PM   #10
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QuoteOriginally posted by Not a Number Quote
This is true for the adapters that have an external flange with a cut-out for lens mount locking pin but I'm speaking of those with an internal flange such as the Kipon adapter:

Kipon Pentax Screw M42 Lens to Pentax K Camera Lens Adapter (with Inner Ring) KP-LA-PXK-PXS
Those I had forgotten about. I was referring to the external flange type.
06-30-2018, 05:00 PM   #11
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QuoteOriginally posted by UncleVanya Quote
The Pentax adapter isn't typically considered flanged. The flanged ones all deny infinity focus although some lenses can be adjusted to compensate by changing infinity focus. Mostly those flanged adapters work well with macro work.
Yes, I realise thatís the shorthand usage, but it does have a small flange. Call me picky.
06-30-2018, 05:03 PM - 1 Like   #12
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QuoteOriginally posted by RobA_Oz Quote
Yes, I realise thatís the shorthand usage, but it does have a small flange. Call me picky.
Picky! LOL. I get the point you were trying to make now. I guess a better way to differentiate would be externally flanged adapters that rest above the mount and internally flanged adapters that rest inside the K mount entirely.
06-30-2018, 10:44 PM   #13
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QuoteOriginally posted by UncleVanya Quote
Picky! LOL. I get the point you were trying to make now. I guess a better way to differentiate would be externally flanged adapters that rest above the mount and internally flanged adapters that rest inside the K mount entirely.
True, but I was also trying to warn the OP about the other types of non-OEM adapters that were on the market Ė the type that does rest inside the K-mount, but which may have other problems.
07-01-2018, 03:29 AM   #14
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QuoteOriginally posted by pschlute Quote
No it doesn't
Yes it does xD.
As already told, I have confirmed this with my K10D already.
When I press the green button there I hear and see the aperture closing temporarily for correct metering.
My K-1 on the other hand does not do this while using the same lens with same adapter.

FYI: The genuine pentax m42 to K adapters are still for sale in Japan, where I got mine.
07-01-2018, 04:01 AM   #15
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QuoteOriginally posted by Snakeisthestuff Quote
Yes it does xD.
As already told, I have confirmed this with my K10D already.
When I press the green button there I hear and see the aperture closing temporarily for correct metering.
My K-1 on the other hand does not do this while using the same lens with same adapter.

FYI: The genuine pentax m42 to K adapters are still for sale in Japan, where I got mine.
No it doesn't !!! Not on a M42 lens.
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