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01-23-2018, 12:42 AM   #1
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Pentax Bayonet Mount with fully automatic diaphragm coupling.

Can anyone tell me which are the Pentax lenses with bayonet mount with fully automatic diaphragm coupling? I have a bunch of super takumars, smc takumars, smc pentax M, pentax A, pentax FA. Since when Pentax started making those? Thanks, Pepe

01-23-2018, 02:05 AM   #2
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With Pentax -A and later lenses (F;FA DFA;DA) the aperture can be operated from the body and all exposure modes (Av;Tv;P etc) will work. If the lens has an aperture ring it must be placed in the "A" position.

Pentax M and earlier lenses do not communicate the aperture to the camera and need to be used in Manual exposure mode, or in limited functionality Av mode (ie wide open only)
01-23-2018, 03:52 AM   #3
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K (bayonet) mount lenses were introduced in 1975. The auto stop down or auto diaphragm feature to allow open aperture TTL metering has always been a feature of K-mount lenses. The introduction of the KA mount ("A" series lenses) in 1983 allowed the aperture to be set from the camera body.

The KA, KAF, KAF2, KAF3 and KAF4 lenses (unless fixed aperture) should allow the f-stop to be set by the camera body.

Refer to:
The Evolution of the Pentax K-mount - Articles and Tips | PentaxForums.com
01-23-2018, 07:01 AM   #4
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The manual of the Pentax LX says that the type of lenses that the LX accepts are: Pentax lenses with bayonet mount with fully automatic diaphragm coupling. This camera accepts Pentax-M 50/1.5, Pentax 50/1.2, S-M-C Takumar 50/1.4 as far as I have tested myself, in the automatic mode. Is it possible that the Pentax lenses with bayonet mount with fully automatic diaphragm coupling may include some of those? Who has tried the LX? Thanks.

01-23-2018, 08:17 AM   #5
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On the k mount film bodies all k mount lenses other than some very special ones are aperture coupled. On digital there are some additional limitations.
01-23-2018, 09:09 AM   #6
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QuoteOriginally posted by Pepe Guitarra Quote
The manual of the Pentax LX says that the type of lenses that the LX accepts are: Pentax lenses with bayonet mount with fully automatic diaphragm coupling. This camera accepts Pentax-M 50/1.5, Pentax 50/1.2, S-M-C Takumar 50/1.4 as far as I have tested myself, in the automatic mode. Is it possible that the Pentax lenses with bayonet mount with fully automatic diaphragm coupling may include some of those? Who has tried the LX? Thanks.
Yes, the answer is essentially "all K-mount lenses".

Some Takumar lenses also had an automatic diaphragm, but this only works on select spotmatic models, and not when adapted to the K mount.

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01-23-2018, 10:35 AM   #7
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All of the K-mount lenses and tele-converters manufactured by Pentax have auto-diaphragm. I'm not sure if the Pentax K extension tubes had auto-diaphragm, however. If it has that movable diaphragm coupling lever sticking out from the mount, then it has auto-diaphragm.

Shutter priority auto-exposure is a different matter. Shutter priority AE means that the user sets and shutter speed and the camera sets the appropriate f-stop. To achieve this, one needs the A or later series (A, F, FA, DA, DFA) lenses with the circular electric contacts on the mount.

01-23-2018, 11:49 AM   #8
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The LX was introduced in 1980 and any K-mount lens with an aperture ring should work with it. You can use lenses without aperture rings but functions will be limited since you can't set the aperture. Screw mount lenses can be used with the adapter but you'll have to use stop-down metering and manually stop down the lens.
01-23-2018, 12:51 PM   #9
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Thanks all. It makes sense.
01-23-2018, 07:07 PM   #10
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if you are using the LX then choose from the "K" series or M or A or F or FA series. Anything that has an aperture ring. The aperture ring must be placed on an f-number, not the "A" setting. This will allow manual and aperture priority shooting with the LX.
01-23-2018, 08:17 PM   #11
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QuoteOriginally posted by pschlute Quote
if you are using the lx then choose from the "k" series or m or a or f or fa series. Anything that has an aperture ring. The aperture ring must be placed on an f-number, not the "a" setting. This will allow manual and aperture priority shooting with the lx.
got it . Thanks.
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