Pentax 50mm Standard Lenses - Part One

Standard, normal, nifty-fifty, the original kit lens can all describe the humble 50mm lens. In part one, John Riley starts the 50mm round up with the history and choices of lenses from the film era, which can still be put to good use today.

Posted: 18/03/2024 - 13:14

Defining the Standard Lens

The human eye is a complex device and adapts as it views in various ways, flitting across a scene, picking out the details it wants to see and assembling a mosaic of images for our brains to decipher. The camera lens is fixed and more literal in its view of the world, but there is still the possibility of creating a lens that approximates the perspective that we see with our own eyes. In other words, one that gives a “normal” view for the camera to record and gives rise to the existence of the ubiquitous standard lens.

In general, the focal length that is considered “standard” for any format is the measurement of the diagonal of that format. This makes, for example, a 6x6cm medium format standard lens around 75mm or 80mm. It makes a 35mm format “full frame” around 50mm (actually 43mm but more of that in a moment) and a crop sensor APS-C format around 35mm. If we use a 50mm lens on a Pentax K-1 and a 35mm lens on a Pentax K-3 then both sets of images should have the same field of view and look the same.

The actual diagonal of the full frame is, as mentioned, 43mm and there is only one standard lens that meets this specification, the SMC Pentax-FA 43mm f/1.9 Limited or the newer HD version of the same lens. Other close contenders are the full frame SMC Pentax-M 40mm f/2.8 and all the full frame 35mm lenses. This is because some photographers prefer a slightly wider “standard” lens, something that is simply reflecting their style and the way they see the world.

The majority view rests with the 50mm, and even that is often stretched slightly. Given that lenses just slightly longer than the 43mm diagonal were easier for early lens designers to make at the highest standards possible of their time, the first standard lenses could be as long as 58mm and even as late as the 1970s could still often be found as 55mm.

So is the 50mm lens (in its broadest sense) just a boring standard view? Not at all, it is a great opportunity to learn our photography and find our own photographic style. 50mm lenses were made in their millions and supplied as standard for decades, being of the highest quality, probably the fastest lens we will own for use in low light and whetting our appetites for more lenses of the same quality from the camera manufacturer. The 50mm can be “abused” optically in various ways, with close-up lenses, filters, extension tubes, bellows units, stereo splitters, teleconverters, front lens converters and whatever else can be found or made and yet have enough reserve of quality to keep the images looking good. The 50mm lens also has fewer elements than any modern zoom, rarely more than 7, and this means fewer lens/air surfaces to reflect stray light and reduce contrast. Flare should be lower, resolution should be higher and images will have more snap to them than anything but the most expensive zooms. Having lived with and maybe mastered our 50mm lens we will know whether we need a telephoto next to follow an interest in sports or perhaps a wide angle lens for more sweeping landscapes.

The first 50mm lens is likely to be around f/2, f/1.8 or f/1.7 and this gives the highest quality blend of properties. In particular, excellent gradation (now including bokeh as a concept) and high resolution along with medium to high contrast. The more expensive, larger and heavier 50mm f/1.4 lenses have a generally different emphasis of qualities, giving higher contrast, perhaps lower resolution but better, grittier low light images. These could be ideal for photo journalists/street photographers looking for crisp, gritty images. The higher contrast of the f/1.4 may make the lenses look sharper, but the very finest detail will not be there. The very fast and bulky f/1.2 lenses are geared up to handling point light sources especially well at the expense of fine detail wide open. However, stopped down they will be as crisp as anything else. This brings us to the rendering of a lens and the very best will have the characteristics that gel with the vision of the photographer and how we view the world. We talk of a lens having “pixie dust” sprinkled on it and this of course refers to the indefinable image qualities that cannot be measured, but we know them when we see them. These lenses are the “keepers” and there are good reasons why the 50mm lens has remained available for a very long time and continues to be a revelation to those who have only ever used zoom lenses with small apertures.

Timeline of Pentax Standard Lenses

Ever since the introduction of the Asahiflex with its 37mm screw mount, there have been virtually endless variations on the humble 50mm standard lens. This timeline lists as many of these as possible, bearing in mind that much of the available information is not detailed as the factories kept very poor records and even serial numbers do not reflect any logical progression.

Using M and earlier lenses on a DSLR

All the lenses listed thus far are manual focus and also have no electronic contacts. As they cannot communicate with the DSLR camera bodies they are used with stop down metering. The process is very simple, for bayonet lenses just focus at open aperture, then set the aperture required on the lens, press the green button on the back of the camera and the lens will stop down with the camera body providing the correct shutter speed.

For M42 screw thread lenses first fit a Pentax Adapter K to the lens, then bayonet it onto the camera and follow the intructions as above. Subsequently, to change screw thread lense they can be unscrewed to remove and another screwed in just as if a screw thread camera were being used. Effectively we are temporarily modicfying a bayonet camera into a screw thread camera.

For the very early 37mm screw thread Asahiflex lenses there was an adapter to use them on the M42 screw thread cameras, but these lenses are regarded largely as collectors items and are unlikely to be in regular use. However, just starting with M42 lenses and all that follow, we can enjoy a reservoir of usable lenses from 1957 onwards, some 67 years of compatibility!

Part Two of this article will cover the MF and AF lenses that have electronic contacts that can communicate with the camera body. This will cover the A series MF lenses and all the AF lenses that follow.

Pentax 50mm Standard Lenses - Part Two or read our overview of the M Series

Members gallery photos using: smc PENTAX-M 50mm F1.7

Add Comment

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