Pentax Lenses - In Detail - Definitions - 3rd-Party - Warnings

As more Pentax DSLR's are sold, an ever-larger number of them are reaching people who are new to Pentax and aren't sure which lenses they can use. By now everyone knows Pentax has the best backward compatibility, but most aren't sure what capabilities you give up with various older lenses. The purpose of this page is to let you know what basic functionality you'll have with any given range of lenses on your Pentax digital camera.

Note that this guide is only for digital SLR's: Film cameras are not covered because they were made with a wide variety of lens mount features, and would require the listing of myriad camera/lens combinations. (For details of all the film camera lens and lens mount variations, see Bojidar Dimitrov's Pentax K-Mount Page.)

 

Pentax Lenses

Pentax lenses discussed here are "K-mount" bayonet lenses. Older screw-mount lenses, also known as "M-42" lenses, can be mounted with an optional adapter: You get only manual focus and manual or aperture-prefered exposure with stop-down metering.

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Details of Pentax K-Mount Versions:

The Pentax K-mount was introduced in 1975 and gathered features over the years. An astonishing amount of forward and backward compatibility has been maintained: You can still use the earliest K-mount lens on the latest digital SLR, but you lose various features with older lenses. This table shows when each series was introduced and what features are and are not present in each one.

Lens Series	"A" Setting	Aperture Ring	Autofocus	Focal Length Data	MTF Data	Full-Frame	Year
"K" series[1]	No	Yes	No	No	No	Yes	1975
"M" series	No	Yes	No	No	No	Yes	1976
"A" series[2]	Yes	Yes	No	No	No	Yes	1983
"AF" series[3]	Yes	Yes	Yes	No	No	Yes	1981
"F" series[4]	Yes	Yes	Yes	Yes	No	Yes	1987
"FA" series	Yes	Yes	Yes	Yes	Yes	Yes	1991
"FA-J" series	N/A	No	Yes	Yes	Yes	Yes	2003
"D-FA" series	N/A	Yes	Yes	Yes	Yes	Yes	2004
"DA" series	N/A	No	Yes	Yes	Yes	Some[5]	2004
Notes: [1] The "K" series aren't actually labeled "K" anywhere — just "SMC Pentax". [2] You can use all exposure modes from the "A" series onward (except for the AF 35-70mm f/2.8 — see note 3). [3] There was only one lens in the "AF" series(!) — the AF 35-70mm f/2.8 — and it was only compatible with one camera, the short-lived ME-F. [4] You get autofocus with all lenses from the "F" series onward. [5] See details of "Full-Frame" below.

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Definitions & Explanations:

Feature	Details
"A" Setting  (metering)	On film cameras, the "A" setting on the aperture ring of Pentax lenses permits shutter-preferred autoexposure and program autoexposure. With Pentax's digital SLR's, lenses that lack the "A" setting require that the photographer use stop-down metering. Pentax provides quasi-automation of this with the "Green Button" feature: Pressing the Green Button (or AF button on some models) momentarily stops down the lens diaphragm and automatically sets the correct shutter speed using the Program autoexposure line and center-weighted metering. This requires that you change the default settings of your camera (through the custom menu) to allow the shutter to fire with a lens off its "A" setting. (See your owner's manual for details.) Spot metering and multi-segment metering are not available when using lenses that lack the "A" setting.
Aperture Ring	All recent Pentax lenses lack an aperture ring entirely. Because the lenses have no aperture ring, the f-stop can only be set via controls on the camera body. These lenses are not usable on many film SLR's but they function properly on all digital SLR's.
Autofocus	Pentax's real autofocus lenses began with the "F" series (the ill-fated "AF" series consisted of only one lens and one camera body that could use it!) "F" series lenses are fully compatible with all the capabilities of Pentax digital SLR's, except for the transfer of MTF data from the lens.
MTF Data	MTF is an abbreviation of "Modular Transfer Function" a mathematical description of the resolving power of a lens. Without going into detail, MTF is an measure of the sharpness of a lens. As most photographers know, lenses exhibit different levels of sharpness and contrast at different apertures. Pentax "FA" series and later lenses contain a computer chip which contains the MTF data for that lens, so you can set the program autoexposure line of your camera to automatically choose the sharpest aperture for any lens you use! (See your camera owner's manual for how to do this.) As far as I can tell, this brilliant feature isn't available from any other camera maker.
Focal Length Data	All lenses from the "F" Series onward transmit focal length data to the camera body. This data is used for flash metering and for the Shake Reduction system in the latest DSLR's. With zoom lenses the focal length data changes as you zoom the lens in or out. To get the best results from the Shake Reduction system with manual focus lenses you must manually enter the lens focal length into the camera (see camera owner's manual for details).
Full-Frame	At the time of this writing (January 2008), all Pentax DSLR's use a 16mm x 24mm sensor which is smaller than the traditional frame of 35mm film (24mm x 36mm). Though larger sensors will almost certainly be introduced eventually, there will be a market for the more economical reduced frame sensors for a long time to come, so in 2004 Pentax began producing some lenses specially for this format. The reduced-image-circle lenses were introduced with the "DA" lens series, so at first everyone assumed that all lenses in the "DA" series series would produce reduced image circles incompatible with full-frame cameras. This turns out not to be the case. The DA 70mm f/2.4 Limited, DA 40mm f/2.8 Limited, DA* 55mm f/1.4, DA*200mm f/2.8, DA*300mm f/4.0 and DA*60-250mm f/4.0 are full-frame lenses (I've received mixed reports on the 35mm f/2.8 Macro). However, some of the other DA lenses (mostly the shorter focal lengths) are known to produce image circles that are too small to be used with full-frame cameras. For the time being this ambiguity is of importance only to the few people who want to use these lenses on film cameras (because these lenses have no aperture ring they are unusable with many film cameras), but it will be of more significance when the inevitable full-frame digital camera arrives. My best guess is that you shouldn't look for it before late 2010; the introduction of the sub-$2000 full-frame camera by Sony in 2009 was a game-changer. The 6-megapixel ist-D retailed for $1500 when it first hit the market and I expect Pentax to get into full-frame when it becomes feasible at that price or slightly higher.

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Other Notes:

Power Zoom:

Some Pentax lenses in the "FA" series had a feature called "Power Zoom", in which the zoom of the lens could be driven by an electric motor (built into the lens). This enabled a variety of features of varying usefulness (see Bojidar Dimitrov's Pentax K-Mount Page for details). The Power Zoom lenses weren't in their own lens series; there were just a few within the "FA" series that carried the additional "Power Zoom" or "PZ" designation. Pentax cameras that support SDM focusing, K10D and later, all support basic Power Zoom capabilities (just basic zooming).

SDM (Supersonic Drive Motor) Lenses:

Although most Pentax autofocus lenses rely on a focusing drive motor built into the camera body, some of the new "DA" series, like the DA*16-50 f/2.8 and the DA*50-135 f/2.8, have the Supersonic Drive Motor, which is a focusing motor built into the lens body. This motor runs on high frequency AC power, making its focusing virtually silent. The K10D, K20D, K200D and K100D Super, K-M, K-2000, K-X and K-7 camera bodies support this feature but SDM lenses will work perfectly on all Pentax DSLR's.

Shake Reduction:

Pentax's version of image stabilization is called "Shake Reduction" and it's built into the camera bodies rather than individual lenses. This means that every lens you put on your camera will work with the Pentax Shake Reduction system. With manual focus lenses you need to tell the camera the focal length of the lens you're using (through the Shake Reduction menu on the camera).

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Third-Party Lenses:

Manual Focus Lenses: To "A" or Not to "A":

The main thing people want to know about is about the compatibility of older, manual focus glass. In general this boils down to one question: Does the third party lens you're looking at have the "A" setting on the aperture ring?

With Pentax's manual focus lenses this is easy to tell — if it's an "A" series lens the answer is yes. If not, the answer is no. With third party manufacturers the issue is less clear cut because they all have different nomenclature. Some differentiate between standard Pentax K-mount, often designated "PK", by labeling A-compatible lenses "PK-A mount". But this isn't universal, so you really need to see the lens to be sure. Be skeptical of eBay auctions that don't show the aperture ring clearly and have sketchy descriptions! Often, the descriptions are sketchy on purpose.

Shooting with Non-"A" Lenses:

To recap: If a lens, Pentax or third-party, doesn't have an "A" setting on its aperture ring, you'll have to set your camera to manual exposure and use the quasi-automated stop-down metering system on Pentax DSLR's. By default, Pentax DSLR's won't let you fire the shutter if the lens' aperture ring isn't set to "A". You need to override this through the custom set-up menu of your camera (this varies between models — see your owner's manual). Once this is accomplished you set the lens to the aperture you want to use and press either the green button on the top of the camera or the AF button on the back, depending on the camera model (still got that owner's manual out?) When you do this the camera will briefly stop the lens down to shooting aperture and set its shutter speed for correct exposure. Yes, even though you've set the camera to manual exposure it will set the shutter speed automatically — that's why I described it as "quasi-automated".

The process is simple once you get the camera's custom menu set up — it takes much longer to describe than to actually do it.

Other Manual-Focus Lens Issues:

Some third-party lenses in the early years of "A" compatibility didn't implement aperture control as perfectly they might have. I have used a few lenses on which the movement of the aperture stop-down lever wasn't quite as finely-tuned to the actual f-stop setting as with genuine Pentax lenses. This means you might get exposures that are significantly underexposed or overexposed. Shooting digital means that you haven't wasted any film; you just need to re-shoot, perhaps applying some exposure compensation. But you should test your lens for exposure accuracy and repeatability before using it in a situation in which you can't re-do shots. My Vivitar 70-210 Series 1 exhibits this problem from time to time, but it's still a fine performing lens optically.

Autofocus Lenses:

In January 2008 Sigma announced the availability of lenses for Pentax which feature HSM (HyperSonic Motor) focusing, similar to Pentax's SDM technology. There is a significant difference: The Sigma Pentax HSM lenses won't autofocus with any Pentax cameras that aren't SDM compatible. This includes the ist-D, ist-DS/DS2, ist-DL/DL2, K100D, K110D and all film cameras. If you use one of these older Pentax cameras with a Sigma HSM lens you'll only have manual focus.

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Incompatibility Warnings:

Avoid Ricoh P-series ("Program") lenses.

You can identify these lenses by a "P" or "(A)P" setting on the aperture ring similar to the A on the A-series Pentax. When the ring is rotated into the "P" (Program) position, it locks in place and you have to depress a small button to get the aperture ring to move again. These lenses have a small ball bearing contact on the rear flange of the lens that will pop right into the hole that holds the AF cam on Pentax autofocus bodies. The result will be that the lens gets locked tight on the body, only halfway mounted.

Early, non-P-Series Ricoh lenses should cause no problem because they have no extra electrical or mechanical contacts.

Avoid third party lenses designed specifically for the program Ricoh cameras.

Beware of third-party lenses designated "KR" or "PK-R" as they are non-Pentax-compatible Ricoh K-mount and can get stuck just like Ricoh lenses. Chinon brand, Albinar, Soligor, Kiron, Tamron, Vivitar and others made such lenses, so when looking at a third party lens, make sure it's for Pentax K-mount and not Ricoh K-mount!

Lenses designated "PK-A/R" are Pentax and Ricoh compatible, and should be safe.

If you get a Ricoh lens jammed on your camera...

If you do get a Ricoh lens stuck on your Pentax camera you can often remove it by inserting a thin feeler gauge between the lens and mount on the lower right-hand side (with the camera pointing towards you) and working it around until you get it between the flange and the offending protrusion. It can take a long time but you will usually (usually!) be able to get the lens off.

But here's what you might have to do if you can't get the lens off: Removing a stuck Ricoh-type lens the hard way.

Some people are reported to have had success modifying Ricoh lenses by removing the offending protrusion to make them compatible.

The Flange Issue:

Some third-party lenses (Vivitar and others) from the manual focus era have an issue that causes problems with later Pentax cameras: A flange which is meant to protect the diaphragm actuation lever but which is much bigger than is really necessary. If your particular lens has this "feature" it will prevent the lens from being mounted on many Pentax cameras, including all the digital SLR's. There's a fairly easy fix for this which I have described on its own page.

Sigma 24-70 f/3.5-5.6:

Older versions of the Sigma 24-70 f/3.5-5.6 autofocus lens are incompatible with Pentax Digital SLR's — They won't autofocus or stop down the lens for shooting and have several other issues. Newer versions of this lens are labeled "ASP HF" and should be OK.

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