Pentax A Series - The Arrival of the KA Mount

In our sequence of articles covering the different of series of Pentax cameras and lenses, John Riley turns his attention to the KA mount and A Series, that featured electronic contacts allowing for communication between camera and lens which opened up a new world of exposure control.

Posted: 19/06/2024 - 08:07

Auto exposure was the key, and in the 1970s there were two distinct groups. The Shutter Priority group used a trap needle system whereby the shutter speed was set by the user and, depending on where the indicator needle for the corresponding aperture was in the viewfinder, the lens would be stopped down to that value. Canon and Konica were two examples of this approach. The Canon AE-1 was perhaps leader of the pack.

Pentax came along with a totally reversed logic around 1972, with the aperture priority system. Now the aperture was set on the lens by the user and the camera would set the appropriate shutter speed, with great precision as now all speeds were available, be it 1/356s or 1/64s or anything else. No longer were the usual full stop values the only ones that could be set. Equally well, whatever was mounted in front of the camera auto exposure could still be used, without the need for any of the complex mechanical linkages that Shutter Priority cameras demanded.

By the late 1970s it was becoming apparent that cameras could be designed with both systems provided. Logically, Av and Tv could be joined by P and programmed auto exposure was the next step. This came to Pentax a little behind such manufacturers as Minolta, but when it arrived it built on the huge success of the Pentax ME Super and LX cameras, needing for its implementation the development of the first electronic incarnation of the K mount.

Thus the KA mount was born, with its electronic contacts enabling Shutter Priority auto exposure mode as well as Program and Aperture Priority. These new lenses were labelled SMC Pentax-A and have an "A" setting on the aperture ring. Set to A the camera can control the aperture. Set to a value the lens works like any previous K series or M series lens. Today, some 41 years later, the A lenses can still be used on any current K mount DSLR and will be fully functional within the limits of the lens. That is, as the A series are manual focus then they are still manual focus. Of course, add the SMC Pentax-F 1.7x AF adapter and even AF is available with lenses nominally of f/2.8 or faster. In practice, this can be stretched and many f/4 lenses will also work.

The beauty of the A series is the full functionality with current cameras in some extremely small packages compared to modern lens design. Many perform just as well as current lenses, perhaps not so surprising as they are computer-aided designs. Let's first have a look at the timeline of the A series and the later P series cameras.

The A and P Series Cameras

The A series arrived in a spectacular way in 1983, with the Pentax Super A (Super Program in the USA), receiving in Europe the accolade of European Camera of the Year 1983. The Super A is the only A or P series camera that has all 6 exposure modes, Av, Tv, P, M, TTL Auto Flash and Programmed Auto Flash. All the following models drop the Tv setting, but do continue with Program Mode.

1984 sees the arrival of the slightly simplified Program A (Program Plus) and the more basic A3 (A3000). The Program A drops the Tv setting. The A3 is the first SLR with a built in motor. It offers just Av and P exposure modes and has DX coding for film speed values. This last point is relevant as many photographers like to rate slide films in particular slightly higher than the indicated speed, to ensure slightly denser colour slides and reduce the chance of blown out highlights.

1985 brings the P30 (P3) with just P and M modes and the more expensive P50 (P5) with A, M and two Program modes, P speed and P depth. Unfortunately, the P50, although a fine camera, did not last long as it was more expensive than the Program A and duplicated most of its functions, so never really found its place.

The P30 was updated in 1988 to the P30n (P3n) and was given back the A setting, as well as P and M. The revamp of 1990 resulted in the familar titanium coloured top plate and the designation P30T, a camera that survived and sold well for many years.

Starting off with the Super A, the development path from the ME Super is very obvious, with push button speed control. The P series cameras take a new path and are highly effective. The most interesting possibilities for the DSLR user are the A series lenses, which are as viable today as they were from 1983 onwards, a remarkable achievement and a fine example of Pentax's dedication to backwards compatibility.

The A Series Lenses

If we examine an A series lens there are a few differences that are immediately obvious. The focusing scale is no longer in a cutout. The lens name is on the sloping front edge of the focusing ring rather than within the filter thread. The index mark is a yellow bubble rather than white. Incidentally, the small index is designed to assist lens changing in dim conditions as it can be lined up with the lens release lever to find the point of insertion. There is an "A" setting on the aperture ring.

The electronic contacts on the mount allow a limited amount of information to be exchanged between camera and lens. When switching the camera on, as this information exchange does not at this stage identify the lens, the camera will ask for the focal length to be entered. This is for the benefit of applying the appropriate amount of Shake Reduction. After that, just use the lens and all exposure modes will work, a minor limitation being that not all EXIF data will be available. The lens should be set on "A" to allow the camera to control the aperture.

Manual focusing is simply a matter of turning the focusing ring until the subject is sharp in the viewfinder or on the monitor if using Live View. The human eye is unfortunately not very good at this, so it needs to be done with care, especially when using the viewfinder. If the camera is set to AF then it will give a confirmation beep when correct focus is hit, which helps enormously. The most accurate way to manually focus is to use Live View and press the centre button of the four way controller. This gives a magnified view and very high accuracy that can be more easily judged. A light press on the shutter release will restore the normal view.

There are also a number of low cost ranges, named as Takumar-A and Pentax-A. These are conventionally coated, so no SMC, but are still capable designs that deliver excellent quality.

All the A lenses are full frame, so if used on a crop sensor APS-C format DSLR then the revised focal length should be used for the SR system. So the 50mm lens should be set at 75mm when asked to input the focal length. If the 1.7x AF adapter should be in use, then the resulting 85mm f/2.8 should be entered as such on a full frame camera, and as the nearest available to 127.5mm on APS-C.

So is it worth using 40 year old manual focus lenses on a DSLR? Absolutely. These lenses can be lighter, more compact, still of superb quality and fully usable with a minimum of caveats for the modern DSLR user. Many of them have attractive characteristics of their own. This is also the era where the zoom lens was taking off in a major way. The A series offers a wide range of zooms, plus an excellent selection of fast primes and Star lenses. Cost should also be attractive, apart from perhaps lenses that become collectors items, thus inflating the price.

We saw what great lenses were available in the M series. Now we can see the fantastic options of the A series, with just that little extra ease of use.

SMC PENTAX-A 50mm f/1.7 Sample Photos

Related Articles

• Pentax K Series - The Original K Mount
• Pentax M Series - The Compact SLR
• Pentax F Series - Introduction of Auto Focus
• Asahi Photo - Pentax Repair Specialist

Members gallery photos using: A Series Lens

Plus Member kasperberghol... kasperbergholt

65 posts
1 years
Copenhagen,
Denmark

Posted 21/06/2024 - 15:15 Link

Great write-up, which explained some things I hadn't understood before - or hadn't considered. Thanks!

After reading the article, I've added the 20mm f/2.8 and 50mm f/1.2 lenses to my wish list - assuming they'll be full-frame compatible on e.g. a Pentax K1?

-- Kasper Bergholt

Moderator

rick rick

263 posts
11 years
Yorkshire

Posted 24/06/2024 - 08:35 Link

All the A Series lenses are full-frame and suitable for your K-1, it's only the DA Series that are APSC.

Pentax KP / Pentax K-01 (Silver)

smc smc

1430 posts
18 years

Posted 26/06/2024 - 07:06 Link

Nice review. I still use a Super A and P50 alongside an MX for film.

Plus Member kasperberghol... kasperbergholt

65 posts
1 years
Copenhagen,
Denmark

Posted 26/06/2024 - 11:34 Link

rick wrote:
All the A Series lenses are full-frame and suitable for your K-1, it's only the DA Series that are APSC.

Great, although that could turn out quite expensive for me

-- Kasper Bergholt

Moderator

rick rick

263 posts
11 years
Yorkshire

Posted 01/07/2024 - 08:56 Link

Quote:
Great, although that could turn out quite expensive for me

Haha, lenses are very addictive!

Pentax KP / Pentax K-01 (Silver)

Add Comment

To leave a comment - Log in to Pentax User or create a new account.