Wednesday, July 05, 2023

Aperture Control and Vintage Lenses

This is a 2023 update to an article written in December 2010, when the temperature was -6 and water pipes had frozen. It's been rewritten for clarity, with clear instructions for using vintage lenses on mirrorless cameras. 

Today we are spoilt by cameras that do the thinking for us. This can be awfully convenient, but it does obscure the photographic process. In this article I'll explain how cameras evolved to allow control over the lens aperture. This knowledge will help you use vintage lenses even on newer cameras.

There are four main types of aperture control that developed alongside SLR cameras: manual, preset, auto, fully automatic.

Manual Aperture

The earliest SLR cameras were fully manual. The ISO depended on the film. The shutter speed was set on the body. In fact, the camera really had only this one job: open and close the shutter as instructed. The iris was determined using the aperture ring on the lens. That's the three main exposure parameters covered. 

When "wide open" at the maximum aperture plenty of light gets to the viewfinder, so you could clearly see your subject. But much of the time you'd want to "stop down" the lens and close the iris. This achieves better image quality and increases the depth of field, so that more of the subject is in focus. (For more on this, refer to my article A Primer on f-Stops and Apertures).

The problem is that with less light getting into the camera, the viewfinder goes dark as well. It's more difficult to accurately focus. The technique to get around this involves getting focus with the aperture open, then stopping down to the desired f-stop. This is "stop-down metering".

(This is where a rangefinder camera has an advantage. The viewfinder window has nothing to do with what light reaches the film/sensor.)

The first innovation was to put a light meter in the camera. A dial or series of lights indicated how far from correct exposure your settings were, so you could adjust shutter speed and aperture.

This allowed cameras to implement an Aperture Priority mode, usually designated by "A" on the mode dial (but instead "Av" on Pentax). Now the camera could automatically set the correct shutter speed, based on the internal light meter.

Preset Aperture

The second type of lens implemented a preset (AKA "pre-select") aperture. This made it easier to move between the open aperture (used to compose the image) and the stopped-down aperture you wished to use for correct exposure.

You can see an example in the photo of the Pentacon 135mm preset, first manufactured in 1971 in the GDR. This lens has two aperture rings. If you turn the knurled ring you adjust the current aperture of the lens. But if you move that ring away from you (in the direction of the green arrow) while rotating, the preset aperture is altered instead. This actually does nothing to the lens diaphragm, but provides a physical stop that prevents turning the aperture ring any further.

preset aperture mechanism

This ingenious mechanical system is simple to use. Move the preset indicator to the aperture at which you wish to shoot. Compose with the aperture fully open. Then, without taking your eye from the viewfinder, turn the aperture ring until it hits the hard stop and click the shutter button. This can be done quickly and accurately.

Auto Aperture

The second innovation was Auto Aperture. These lenses incorporate a spring that holds the aperture open. A small pin on the lens mount stops the lens down when depressed. You can see the pin at the bottom left of the photo below.

Auto Aperture A setting

The pin allows the camera body to stop down the lens, a simple mechanical solution to the problem. A further innovation allowed a depth of field preview, since this is nothing more than stopping down without actually taking a picture. 

In order to use these lenses on cameras without the newfangled auto mechanism, a rotating switch selected between two settings. Use "A" when you have a body that can use the pin; "M" otherwise. The next photo of the Vivitar Series I 28mm f/1.9 shows the sliding switch set to Manual.

(Note the silver rim around the M42 mount. That is a simple adapter that converts the lens to the Pentax K-mount bayonet system. Sometimes I forget that these are not native K-mount lenses!)

Auto Aperture M setting

Automatic Aperture

The next historical milestone was the development of electrical communications between body and lens. This facilitated shutter-priority mode, where the photographer could set the shutter and the camera would automatically set the correct aperture based on the light meter. Soon would come Program modes and further automation.

The universal M42 mount was abandoned as too limited. Each manufacturer differentiated their new offerings from the competition by adopting their own proprietary mount systems. That's how we ended up with different lens mounts for Pentax, Nikon, Canon, Olympus, etc. What a shame that they didn't cooperate on a standard!

Besides electrical communications, a further benefit of the new mounts is that they used a locking bayonet system rather than a screw-in design. Lenses became faster and easier to change.

The fully-automated aperture coupling meant that there was no longer a need for the aperture ring on the lens, since this function could also be handled by the camera body. Lenses designed exclusively for digital cameras became simpler to build, without all of the mechanical aperture shenanigans.

(Although the did incorporate auto-focus, which is a different matter!)

The Picture Today

Computer-aided design processes and composite material have achieved optical standards heretofore undreamt of. As a bonus, distortion and vignetting can be automatically corrected by the camera's firmware, since it can read these coded values from the lens. If you want optical perfection, use a contemporary lens designed for your camera system.

But perfection is not everything. A vintage lens might also have distinctive image characteristics that can be used artistically. Flare, coma, and other "imperfections" can become expressive attributes, as can different bokeh looks. Sharpness and contrast are not the only goals, especially for video. Besides, many people, myself included, find an aperture ring on a lens to provide a more tactile and enjoyable photographic experience.

We can thank the flexibility of mirrorless cameras for re-introducing photographers to the wonders of vintage lenses. The short flange distances of these systems allow inexpensive mount adapters to couple historic mounts to contemporary camera bodies. The majority of these are dumb adapters, with no communication couplings. So we have come full circle, back to using manual, preset, and auto lenses!

As a by-product, certain lenses have become very popular, driving up prices on what were originally bargain basement deals. When the price of a vintage lens equals a contemporary model, one really has to start questioning the value proposition. That old lens might be out of alignment, have scratches on lens elements, embedded dust, fungus, or fog.

Instead you can buy a brand-new fully-manual lens from Chinese brands like TTArtisan, 7Artisans, Venus Laowa, or Kipon. Sigma even markets a series of "Contemporary" lenses which are fully automatic but sport an aperture ring.

Truly we are spoilt for choice.

Using Vintage Lenses on Mirrorless Cameras

First, you will need the correct mount adapter. I've had good luck with the inexpensive K&F brand. I have three of these for L-mount: M42, Pentax K-mount, and Contax-Yashica. These are "dumb" adapters with no electronic couplings. 

Set the camera's mode dial to "A" for aperture priority. Set your ISO. Use the aperture dial on the lens and the shutter speed will be automatically set by the camera. (You can of course use fully manual operation, but this is easier.)

If your lens is Auto Aperture, be sure the switch is set to M since your camera will not have a mechanism for the pin. If this is set incorrectly, the lens will shoot wide open all the time. This can also happen if the lens is faulty and this mechanism is broken. Sometimes people even glued the switch into place... yikes!

Now, open up the lens aperture fully and compose. Get focus. Stop down the lens to the f-stop you prefer. Take the picture. Easy.


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