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11-25-2009, 08:43 AM   #1
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GEneral question about K20D and older lenses

I'm new to Pentax, although not new to photography. One of the main reasons I bought the K20 was because of the ability to use all Pentax lenses. I've noticed that there are various series of lenses (DA,M,F, etc), so I was just wondering about how the older lenses work with the K20.

Do any of the older lenses allow any of the electronic modes to work, or does the camera always have to be used in manual mode? Also, does autofocus work with any of the older lenses?

Last edited by jeryst; 11-25-2009 at 08:49 AM.
11-25-2009, 09:27 AM   #2
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Any lens that is F, FAJ, FA, FA* DA, DFA, DA, DA* will auto focus and auto expose with the camera.
Older lenses like the A and A* will auto expose but not auto focus (no AF screw drive).
Older than that, M, K and M42 will be manual everything. You can use these lenses in M mode and Av mode but metering can be off sometimes when using the Green button.
11-25-2009, 10:34 AM   #3
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Thanks. I'm also a little confused about the mounts. I see bayonet, K, PK,M42, etc.

Which ones will work on the K20 without adapters?
11-25-2009, 10:50 AM   #4
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All mounts will work, but the m42 requires a bayonet adapter because it is a scew mount, not bayonet.

11-25-2009, 11:13 AM   #5
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Morning, In general you will only find 2 Pentax mount types. The M42 (ended around 1975) and the bayonet mount (started around 1975) and often referred to as the K mount and its various variations.
M42 mount - works with a adapter available from Pentax (about $30), others are available but build quality varies so that registration distance varies and on some the lens either does not achieve infinity on focusing. A number of lens manufactures still make this mount - including Zeiss.

Hin's Tech Corner: Genuine Pentax M42 to K Adapter

Bayonet or the K mount - This has been adapted for various reasons over the years, but they all work on all the camera bodies. The mounts K mount, KF mount, KA mount, KAF mount, KAF2 mount, KA2 mount, "Crippled" KAF mount, "Crippled" KAF2 mount, all work well. Here is a complete description of them...

Pentax K mount - Wikipedia, the free encyclopedia
Watch out for the R-K mount. from Ricoh. There is an extra pin that gets stuck in the camera, and removing the lens sometimes need to be done by a camera shop (disassemble the camera). So just steer away from Ricoh or R-K mounts (note - there are not that many of them).

Which ones will work on the K20 without adapters?
Any of the Bayonet or K mounts - with the exclusion of the R_K (above note).

Note - I have a Pentax SMC A 50/1.7 introduced in 1983 that works perfect (SMC - Super Multi Coating). It is a manual focusing with automatic aperture. Also an FA 31/1.8 introduced in 2001 that is auto focusing and aperture (custom setting for the aperture ring should to be set "enabled" in the K20 menu).

hope that helps...

Last edited by interested_observer; 11-25-2009 at 11:26 AM.
11-25-2009, 11:39 AM   #6
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A quick note regarding Ricoh lenses with the troublesome "Ricoh Pin". These lenses were made for Ricoh program exposure cameras and have a prominent "P" on the aperture ring. The "pin" varies from an actual spring-loaded pin to a captive, spring-loaded ball bearing. In both cases, the "pin" will jam into the AF drive notch on the KAF mount. The ball type is a less likely to cause a problem, while the pin type is usually "fatal".

Detecting these lenses is pretty easy.
  • All have the bright green "P" on the aperture ring
  • Ricoh brand are labeled Rikenon-P
  • 3rd-party lenses (Sears, Focal, Vivitar, etc.) usually have Ricoh, KR, or RK on the lens or mount
  • The pin itself is pretty prominent and easy to spot if you are familiar with the mount
Rikenon lenses other than Rikenon-P (Rikenon, Auto-Rikenon, and XR Rikenon) are often excellent optics and perfectly safe on your camera. If, by some accident, you find yourself owning a "P" lens, all is not lost. The pin can be surgically removed.


(Resident Ricoh fan boy...)
11-25-2009, 11:38 PM   #7
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the replies above hafe just about covered it all.

here is a summary with a few other things to note.

M42 lenses,
- when used with a pentax adaptor can be used in Av mode and Manual mode. As noted above they sometimes require having an exposure compensation set on the camera, and some bodies K10D and K20 D have exposure variations as a function of F stop due to the behavior of the standard focusing screen.
- when used with an after market "flanged" adaptor you cannot achieve infinity focus.

K mount lenses
- can be used in Av mode but only at maximum aperture when properly mounted on the camera, or in M mode, metering with the green button.

Note K mount pentax lenses include SMC Pentax, SMC-M pentax lenses and Takumar Bayonette lenses

Derpending on the body used, flash functions can be severly restricted with these lenses. Only the *istD and DS have a second flash metering sensor to support TTL flash, which does not need to know lens aperture to make flash exposures because it measures reflected light directly off the sensor plane. All other bodies can only shoot manual flash or if using an external flash with it's own sensor "Auto" mode

KA mount lenses (SMC-A lenses)

- when using these with the lens in the A setting, can perform all exposure modes and all flash modes, but are manual focus
- when not in A mode on the lens perform as K mount above

KAF mount lenses, which include SMC-F and SMC-FA lenses,

- these support all modes above when lens is in A mode
- are Auto focus
- behave as K mount when not in A position

KAF2 mount lenses

- these are KAF mount lenses with 2 additional contacts for power zoom. On a DSLR the power zoom works with the zoom ring, but none of the power zoom functions such as zoom during exposure and image size tracking in the camera are implemented.

You then have 2 varients.

There are what I call KAF-J lenses, these are KAF mounts but without manual aperture couplings. The work fine on most pentax bodies after 1983 but there is no manual aperture for older bodies like the K series cameras

The new SDM lenses have a KAF2 mount, but like the KAF-J lenses have no aperture coupling so cant be used on K series bodies

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