Stopped down or full aperture metering – why it still matters for users of mirrorless cameras today

For a single lens reflex camera or a lens manufactured after 1975, full aperture vs stopped down metering is a non issue. But it was a key differentiator between 1965 and 1975. And if you’re considering mounting an old lens (manufactured before 1975) on a mirrorless camera, it may still impact you.

On a single lens reflex camera (SLR), the photographer composes the picture on a mat focusing screen, where the image formed in the lens is projected. This layout has all sorts of advantages, but the viewfinder tends to get too dark for focusing when the lens aperture exceeds F/8, and at smaller apertures (F/11, F/16), even composition becomes impossible.

Therefore, the best practice in the 50’s was to open the lens at the widest aperture, focus carefully, and then rotate the aperture ring to stop down the lens at the aperture needed to expose the picture optimally. It worked, but it was slow.  The process was easy to automate, and that’s what aperture pre-selection systems do.

Aperture pre-selection mechanism

Their goal : let the photographer compose and focus at full aperture, and then stop down at the last fraction of a second, when he/she presses the shutter release. Practically, the diaphragm stays wide open, until the shutter release mechanism  (through various cogs, springs and levers) activates a rod in the lens which closes the diaphragm to the aperture pre-selected by the user.

Two implementations

  • manual pre-selection : the lens stays stopped down after the picture has been taken. The pre-selection mechanism has to be re-armed by the photographer if he/she wants to return to full aperture; it’s a slow process (shoot, rearm the shutter, rearm the lens).

    This big lever on this Nikkorex lens has to be pushed down to re-arm the pre-selection system after each shot
    This big lever on this Nikkorex lens has to be pushed down to re-arm the pre-selection system after each shot
  • auto pre-selection: the pre-selection mechanism does not need to be re-armed after each shot. The lens returns automatically to full aperture after each shot (that’s why lenses from the 1960-1975 period are often labeled “Auto”). It’s transparent for the user, who can operate faster and with a better chance of catching the decisive moment.

    M42 Lens mount - this lens is designed for "auto" preselection. It stays at full aperture until the pin is pushed to stop down position.
    M42 Lens mount – this lens is designed for “auto” preselection. It stays at full aperture until the pin is pushed to force the lens to a stop down position.

Through the Lens (TTL) metering

Aperture preselection solved the problem of composing and focusing at slow apertures, but the introduction of CdS cell meters to evaluate the illumination of a scene Through The Lens (TTL) brought a new set of challenges: the camera needed to know how open the diaphragm was going to be when the picture is finally taken. There were two ways to do it:

  • after the photographer had set the aperture, he had to press a dedicated lever to stop down the lens, and only then would the camera evaluate the illumination of the scene. It’s stopped down metering.
    Technically, it’s the quick and dirty answer:  the metering system of the camera does not need to know the value of the aperture pre-selected on the lens. It just measures the light going through the lens when stopped down. The pre-selection lenses don’t need to be modified – they simply work. But it’s cumbersome for the user:

    • it’s a step back – aperture preselection had removed the need for the photographer to stop down the aperture before pressing the shutter release. Now it needs to be done again.
    • the viewfinder is darker during metering (the photographer loses contact with the action, he can’t adjust the focus, and it’s difficult to see needle of the meter) – you cannot compose or focus and adjust the exposure at the same time.
    • it’s a disaster from an ergonomics point of view. Even in the best implementations, the photographer has to maintain the lens stopped down by pressing or lifting a dedicated lever on the camera’s body, while trying to turn the aperture ring or the shutter speed knob to adjust the exposure. You need three hands for this type of gymnastics.

      The Canon FT/QL and the Pentaxx Spotmatic SP both offer Stopped Down Metering. To determine the exposure, the photographer has to push the big switch to the left (Canon) or to lift the switch in the red circle (Pentax) - which is not a very natural movement. You wish you had three hands.
      The Canon FT/QL and the Pentaxx Spotmatic SP both offer Stopped Down Metering. To determine the exposure, the photographer has to push the big switch to the left (Canon) or to lift the switch in the red circle (Pentax) – which is not a very natural movement. You wish you had three hands.
  • full aperture metering is transparent for the user. The diaphragm is stopped down a fraction of a second before the shutter curtains open and the picture is actually taken. The lens stays at full aperture all the time, including during the exposure determination.
    But for full aperture metering to be possible, the lens has to communicate the aperture pre-selected by the user to the metering system in the camera body, so that it can determine the right shutter speed/aperture combination.
    Most vendors chose to add a new dedicated lever inside the lens mount (this solution was chosen by Canon, Minolta, Olympus and Pentax).

    Pentax K mount: Aperture control lever (i); Aperture simulator (ii): Source:pentaxforums.com
    Pentax K mount: Aperture control lever (i);
    Aperture simulator (ii):
    Source:pentaxforums.com

    A few other vendors chose to simply modify the design of the aperture ring of the lens, and use it to transmit the aperture value to the camera’s metering system. At the beginning, Nikon used an external fork (the “rabbit ears”) screwed at the periphery of the aperture ring to communicate the pre-selected aperture to a pin connected to the metering system in the body.

    Before the adoption of Auto-Indexing, Nikon lenses used a metallic fork ("the rabbit ears") to transmit the preselected aperture to the metering system of the camera.
    Before the adoption of Auto-Indexing, Nikon lenses used a metallic fork (“the rabbit ears”) to transmit the preselected aperture to the metering system of the camera.

    Later, Nikon redesigned the aperture ring to add  a small protruding tab at its back, and this tab moved a sensor on the circumference of the body’s lens mount (Nikon Auto Indexing or “AI” lenses). Nikon’s system is similar (in its principle) to Fuji’s implementation of full aperture metering on the m42 universal mount of the ST801 (pictures below).

Fujinon lens - the aperture ring is designed with a small tab which transmits the aperture pre-selected by the photographer to a rotating ring on the camera's body.
Fujinon lens – the aperture ring is designed with a small tab which transmits the aperture pre-selected by the photographer to a rotating ring on the camera’s body.
Fujica ST 801: Fuji's version of the m42 lens mount has a ring at the periphery - the little pin in the red circle is pushed by the tab protruding from the aperture ring of the lens. That's how the preselected aperture is transmitted.
Fujica ST 801: Fuji’s version of the m42 lens mount has a recessed, spring loaded rotating ring at the periphery – the little pin in the red circle is pushed by the tab protruding from the aperture ring of the lens. Any change to the pre-selected aperture on the lens will be transmitted to the camera.

Mounting an old lens on a mirrorless camera

When the photographer is using an old lens through a lens mount adapter, the cameras  needs to work with the lens stopped down (only semi-auto and  aperture priority automatic exposure modes are supported). There are none of the inconveniences associated with stopped down aperture on a reflex camera: on a mirrorless camera, the viewfinder always shows the image as it will be exposed, and if the exposure parameters (aperture, shutter speed and ISO) are correctly set, the image will be perfectly legible in the viewfinder, even if the lens is set a f/11.

But the challenge is to force an old lens to operate stopped down:

  • lenses designed for full aperture operations and stopped down metering (typically the m42 lenses with auto-pre-selection and the Canon FL) have a slider to switch off auto-preselection and operate permanently at stopped down aperture, in a manual mode. When mounted on a mirrorless camera through a lens mount adapter, they need to be switched to “manual”.
     Lenses of the 1965-1975 era often had an auto/manual switch - by default the operated at full aperture but could revert to manual if mounted on an older reflex camera.
    Lenses of the 1965-1975 era often had an auto/manual switch – by default they operated at full aperture but could revert to manual if mounted on an older reflex camera.

    The "manual" mode has to be switched on when used on a mirrorless camera.
    The “manual” mode has to be switched on when used on a mirrorless camera.
  • Nikon lenses  – the diaphragm of the Nikon lenses is opened at full aperture when the camera is mounted on a Nikon camera (the camera side of the mount has a lever which forces the lens open), but is stopped down when the lens is removed from the camera, or  mounted on an adapter deprived of the full aperture lever.  Which is perfect if you’re mounting the lens on a mirrorless camera.
  • Canon FD – when the lens is removed from a Canon camera, the diaphragm command is decoupled (the lens stays at whatever aperture it was pre-set the last time it was on a Canon FD camera). The adapter needs to be designed with a pin that will force the lens to stop down  when mounted on the adaptor.
Lens mount adapter for Canon FL/FD lens - the pin in the red circle pushes a lever on the lens and will force it to stop down.
Lens mount adapter for Canon FL/FD lens – the pin in the red circle pushes a lever on the lens and will force it to stop down.
  • Fuji’s EBC-Fujinon lenses are highly regarded, but the brand’s implementation of full aperture metering on the m42 mount presents two problems for modern mirrorless camera users:
    • most of the lens mount adapters receiving m42 lenses do not leave room for the aperture ring’s protruding tab of Fuji’s lenses. The lenses cannot be fully screwed down on the adapter and as a consequence may not focus to the infinite,
    • Fuji’s lenses don’t have a “manual” position and cannot be forced to operate stopped down on their own (that function was provided by the Fujica camera itself, not by the lens). There are work arounds to both issues, some nice, some ugly, but a lens mount adapter designed specifically for Fujica m42 lenses still has to be developed.

New-York City - Central Park - Fuji XT-1 - Canon 35-105 f/3.5 lens with Fotasy adapter
New-York City – Central Park – Fuji XT-1 – Canon 35-105 f/3.5 lens with Fotasy adapter

Exposure Metering: Multi-Spot or Matrix


All film cameras have to live with the same design constraint: their shutter and their diaphragm are built in such a way that, for a given picture, the shutter speed and the aperture are the same for each square millimeter of the film. There is no way for the shutter of a film camera to block the light in excess in a particular zone of the scene, or to stay open longer only for the portion of the scene located in the shade. At some point the researchers of Canon were rumored to be working on an LCD based shutter, which could to exactly that, but the research never materialized.


Olympus OM-3
Olympus OM-3. Picture: Wikipedia


Since the shutter only works in an all or nothing, one-duration-fits-all mode, some zones of the film will receive more light than the optimum, and others will receive less. Films have the ability to give acceptable results when portions of the scene are a few f: stops brighter and a few stops darker than the optimum (that’s the exposure latitude of the film). As a consequence, the exposure metering systems of the cameras are calibrated to determine the correct exposure for the portion of the subject located in the mid-tones, with the expectation that the film will have enough exposure latitude to render the highlights and the shadows correctly.


Unfortunately, in some cases, the brightness range of the scene greatly exceeds the exposure latitude of the film (think of the backlit portrait at sunset with the sun in the frame); supposing the photographer can not reduce the brightness range of the scene – using a flash or a reflector to bring more light to the subject, for instance, the exposure parameters will only be optimal for a subset of the scene, the highlights or the shadows, and the rest of the picture will be burned or left in the dark.


When cameras started being equipped with Through the Lens (TTL) metering systems in the sixties, most of the manufacturers opted for Average or Center Weighed Average Metering. Those metering systems were not adapted to high contrast scenes, and the photographers had to put their experience to good use and take control manually of the exposure metering process. If they had automatic cameras, they had to use exposure lock or exposure compensation systems. The alternative – measuring the brightness of a very narrow section of the scene with a spot meter, was not easy to master for the average photographer. Elaborate exposure determination procedures such as the “zone system” were adapted to small format cameras using roll film, but their complexity put them out of reach from the majority of photographers.


The Olympus OM-4 and the Nikon FA


In 1983, two cameras manufacturers tried to address the problem of high contrast/high brightness range scenes, and they chose two very different approaches.


Olympus tried to make the principles of the zone system accessible to more photographers, and developed a multi-spot system for the new OM-3 and OM-4 cameras. With the new OMs, the photographer could make up to eight successive spot measurements, whose result were presented in the viewfinder on an analog bar scale showing each individual result and the average. The cameras also had a “shadow” and a “highlight” push button, letting the photographer compose his picture following the principles of the zone system.


The photographer Ken Norton described the process in his blog:


Olympus OM-3 and OM-4: exposure metering controls
Olympus OM-3 and OM-4: exposure metering controls. Picture: Wikipedia


“for example, I can take a spot reading of a highlight, a midtone and a shadow. Three dots will appear on the display. If I’m using a film with six stop exposure range, I’ll make sure that all three dots appear within the +/- 3 stop marks. Of course, I can bias my exposure to place a highlight or shadow anywhere I want on the scale. Digital cameras are capable of producing a histogram of an image. The multi-spot scale, with the “dots” is a poor-man’s variation of the histogram where we are able to define our bright areas and dark areas of a scene and like a histogram we are able to move these points around to place them within the acceptance range of the film.


You can read more about the subject, and see actual pictures of the viewfinder on Ken’s pages.


Nikon chose a totally different approach. In the first iteration – the Automatic Multi Pattern (AMP) of the Nikon FA – the camera was equipped with a database containing the mathematical description of thousands of potential pictures, with the exposure value to be used in each situation. The light meter was divided in five zones (a large central zone, two zones at the bottom left and right, two zones at the top, left and right also), and the electronic circuit would correlate the exposure value of each zone with other elements such as the focal length of the lens to define the characteristics of the scene, and associate it with one of the many typical pictures described in the database of the camera.


Nikon FA (the round knob controlling the exposure mode ( matrix or center weighted) is on the right side of the lens mount, at the top on this picture
Nikon FA (the round knob controlling the exposure mode ( matrix or center weighted) is on the right side of the lens mount, at the top on this picture


The FA could also be operated in a more conventional Center Weighted Metering mode, and in all honesty, the results of the AMP system were not that different from the center weighted mode. But the system required no intervention and no expertise of the user, and was rapidly made more efficient with the addition of more metering zones and the capture of more parameters (focusing distance, color of the subject, for instance). Current Nikon cameras have a color sensor dedicating to metering, with more than 1,000 metering points. Equivalent systems have been developed by Canon, Minolta and the other manufacturers, under different names: Canon’s system is “evaluative”, and Nikon’s AMP is better known now as “Matrix metering”.


Modern digital cameras all use elaborate variants of matrix or evaluative metering as their default exposure mode, and give good results in a huge majority of cases. They use so many parameters that it’s sometimes very difficult to understand how the camera chose a particular exposure value; in doubt, photographers can visualize the picture they’ve just taken on high definition displays, and use histograms to analyze the exposure of their pictures. Olympus’ Multi-Spot system happened to be too complex for the huge majority of photographers, and left no legacy.


More about Exposure and Metering


Cambridge in Colour. A good (and free) on-line tutorial about digital photography.
A good book about exposure: “Exposure“, by Chris Weston.


Destin- The beach (Nikon FA- Nikkor 24mm AF - Kodak Ultramax) Sept.09
Destin- The beach (Nikon FA- Nikkor 24mm AF - Kodak Ultramax) Sept.09

The Nikon FE2: one of the very best manual focus SLRs ever.


Launched in 1983, the successor of the FE had a relatively short sales career, but a long legacy. It can be argued that the Nikon FM3a, sold from 2001 to 2006, is much more a descendant of the FE2 than of the FM2.

 

Nikon FE2 - Shutter
Nikon FE2 – The titanium blade shutter was the most advanced at the time of the camera’s launch, with a top speed of 1/4000 sec and a flash sync speed of 1/250 sec.


In 1977, a few years after Olympus initiated the compact SLR revolution, Nikon presented the FM. Like the Olympus OM-1, the FM was a compact semi automatic camera with a mechanical shutter, which could be equipped with a motor drive. But contrarily to the OM-1, which still relied on a CdS light metering system and on mercury batteries, the FM used modern gallium photo diodes and silver oxide batteries. It also benefited from a vertical blade metallic shutter, and the exposure metering was relying on 3 LEDs instead of the more conventional match needle arrangement of the OM-1. Solidly built and reliable, the FM was very successful commercially, and the ancestor of a large family of models whose production only stopped in 2006.

Nikon FE2
Nikon FE2

The FE from 1978 is the automatic exposure version of the FM. It looks very similar to the FM, but instead of LEDs, it uses two needles to show the shutter speed selected by the photographer (semi-auto mode) and by the automatic exposure system (aperture priority auto mode). In 1982, the FM became the FM2, receiving a new mechanic shutter with titanium blades, which could reach 1/4000 sec and had a flash synch speed of 1/200 sec.


One year later, the FE2 was launched. Its titanium shutter is an improved and electronic version of the FM2’s, with a X synch speed now reaching to 1/250 sec. The FE2 also benefits from a modern on the film (OTF) flash metering system (that the FM2 never got). The FM/FE range of products was extended the following year with the presentation of the Nikon FA, which added matrix metering (a world premiere), a programmed exposure mode and trade the brass prism cover of the FM/FE models for a polycarbonate one. Both FE2 and FA were discontinued in 1988. The FM2 lived longer, and was ultimately replaced by the FM3a, which merged the mechanical shutter of the FM2 with the electronics of the FE2.


Using the FE2 as an every day camera


Reasonably light and compact, the Nikon FE2 is very solidly built, and very nicely finished. Compared to a previous generation model like the FM, the FE2 has smoother commands. The viewfinder is typical from a pre-high eye point construction – the enlargement factor is high (0.86) for a good focusing precision, but the frame coverage is limited (93%), and the eye point is very short (14mm), which could be an issue for photographers wearing glasses. Even with thin glasses, it’s impossible to see 100% of the image projected on the focusing screen without having to move one’s eye ball right to left and left to right: you only perceive 90% of the focusing screen when you look straight into the viewfinder, which compounded with the rather limited frame coverage, ensures that you’ll have a wide safety margin on both sides of your prints.

 

Nikon FE2 / Olympus OM-1n
Nikon FE2 / Olympus OM-1n – The FE2 is larger, but not significantly.


The determination of the exposure is very conventional for a camera of its generation, with a center weighted measurement provided by two silicon photodiodes. In automatic mode, a needle indicates the speed selected by the exposure system of the camera on a large scale at the left of the viewfinder. The photographer has multiple ways to override the automatism: he can memorize the exposure (pushing the self timer lever towards the lens), apply a correction factor on the film speed selector (from -2 up to +2EV), or switch to semi-auto mode. In this case, a second needle – larger and transparent – appears in the viewfinder, showing the shutter speed selected by the photographer. In a very simple matching needle arrangement, the photographer just has to align the meter needle with shutter speed needle. The shutter speed knob is much smoother than on the FM (in the FE2 the shutter is controlled electronically), and surprisingly the camera is more pleasant to use in semi-auto mode than the FM. No wonder that Nikon derived the exposure control system of the FM3a from the FE2’s and not from FM’s.


 

Nikon FE2 with MF-12 back
A very clean Nikon FE2 with the MF-12 data back – All the commands are grouped on the top plate – with the exception of the depth of field preview and the exposure lock levers, located at the right of the lens mount. A very simple and efficient layout.


Conclusion


Powered by two easy to find LR44 silver oxyde batteries, the camera also operates without battery at a speed of 1/250sec. Compatible with any AI, AIs and AF lenses, it’s still perfectly usable today.


Less rugged than its FM and FM2 cousins (it has an electronic shutter and a potentially more fragile match needle metering system), it is more pleasant to use and can respond efficiently to a larger variety of photography opportunities. Like the FA and the FM3a, but unlike the FM2, the FE2 benefits from a modern through the lens (on the film or OTF) flash metering system, compatible with the flash units currently sold by Nikon.

 

Nikon FE2 with MF-12 back
Nikon FE2 with the MF-12 back. The MF-12 back was designed for the FM/FE cameras, which did not have internal synchronization contacts for a data back inside the film chamber. Hence the need for an external synchronization cord. The FE2 could also use the MF-16 data back, which did not need the external sync cord.


Its automatic exposure system is very easy to override, and does not get in the way. The matching needle system in the viewfinder is very informative, easier to read in the sun light than the LEDs of the FG, and than the small LCD display of the FA.


With the F3, the FE2 is probably the most usable Nikon camera of the early eighties.


How much for a Nikon FE2?


The Nikon FE2 is a very good automatic exposure film camera, and its reputation has obviously an impact on its price. Specialized retailers like KEH sell it between $130 (Bargain) and $270 (Top Condition). As usual, prices are a bit lower on eBay, but the FE2 does not seem to sell for less than $100, with peaks up to $180 for very nice items.


There are few alternatives to the FE2: the more recent FM3a is much more expensive (typically from $400 up to $700) and the FE, with its modest shutter and no OTF flash metering, is far more primitive and more difficult to recommend.



More about the FE2


Photography in Malaysia


Tree trunk
Tree trunk – Along the Nickajack Creek – Smyrna, GA (Nikon FE2, Nikon 50mm lens, Kodak CN400 film.

Why are manual exposure cameras worth more than automatics ? (Intro)


The facts


Let’s take three lines of manual focus cameras which still have a very active second hand market today: the Leica R series, the Nikons FM & FE and their derivatives, and the Olympus OM-1 & OM-2 and their “single digit” descendants. Each line contains automatic exposure cameras (Leica R4, R5, R7; Nikon FE, FE2, FA; Olympus OM-2, OM2s, OM4, OM4t), and manual exposure cameras (Leica R6, R6.2; Nikon FM and FM2; Olympus OM-1 and OM-3).


For a given generation of camera, manual exposure models are almost always worth more than their automatic exposure siblings.


Average retail price of a camera in Excellent Condition (source: a reputable specialist of used photographic equipment)

Brand Manual Camera Auto exposure Camera
Leica R6.2: $ 999 R7: $ 550
Nikon FM: $ 190 FE: $ 170
Nikon FM2: $ 245 FE2: $ 199
Olympus OM-1: $ 150 OM-2: $ 190
Olympus OM-3: much more than $500 * OM-4: $ 235
Olympus OM-3T: much more than $1,000 * OM-4T or TI: $ 450


More after the jump