Pros: Low price. Lightweight. Incident and reflected light metering on a single unit.
Cons: A bit fragile. No viewfinder for reflected light metering. Film speed setting drifts.
Sekonic's L-208 light meter, now called the "Twinmaster" but formerly the "Twinmate", is an old-fashioned electro-mechanical dial gauge lightmeter. A sliding integrating hemisphere, which Sekonic calls a "lumisphere", allows the meter to be used for incident metering; sliding the sphere away switches the meter over to reflected light metering, with about a thirty-three degree field of view.
The L-208 weighs under two ounces and comes with an adapter for standard-sized camera accessory shoes. Usage is simple: a push of a button causes the exposure needle to jump, and the correct exposure is determined by needle matching and a simple geared analog computer. The needle stays in place for fifteen seconds following a press of the button. Film speed is dialed in ahead of time, moving some of the text clockwise or counter-clockwise to adjust the relevant factors of two. A second button allows the user to test battery power before a shoot.
Why a light meter?
The simplest cameras on the market, single-use "disposable" cameras, have no means to adjust lens aperture or exposure time. They're loaded with high-speed print film (usually ISO 400 or greater) and rely on the film's exposure latitude to make decent-looking photos under snapshot conditions. Overexposure causes slide film highlights to "blow out" and go transparent and underexposure causes print film to be black; improper exposure, especially overexposure, of digital sensors is even worse. More serious cameras thus allow adjustment of exposure by adjustment of shutter speed and aperture.
The dark areas of film with (print film's low) five-stop range contain sixteen times less light than the light areas. The difference between the darkest shadows and the highlights on a slide can be a factor of sixty-four or more. A meter allows one to expose a scene so that the highlights (for slide film shooters) are not lost due to overexposure and good use is made of the film's dynamic range. ("Good use" depends in part on the artistic desires of the photographer!) One can also underexpose slide film slightly to saturate colors or overexpose a bit to wash them out.
Reflected light metering--the most familiar, due to the ubiquity of SLRs with TTL metering--allows the photographer to choose whatever area is being metered to be rendered (color aside, considering density only) as a neutral grey. Incident-light metering--done by pointing the meter back at the camera in an area receiving lighting like that of the subject--establishes an exposure such that neutral 12% grey objects are rendered as neutral 12% grey.
Why a stand-alone light meter in 2009?
Two generations of amateur photographers, myself included, learned the craft using single-lens reflex (SLR) cameras with through-the-lens (TTL) metering. These cameras direct some of the incoming light to a CdS phtoresistor using a beamsplitter; the rest is directed through the viewfinder. The correct aperture, given a set shutter speed, is determined using an analog computer and displayed in the viewfinder with a needle; allowing composition and exposure to be conveniently done at the same time; later models automated this task. As long as battery adapters are used to bring voltage down to proper levels--these cameras were designed for mercury cells!--TTL meters in decades-old SLRs still work to accurately guide proper exposure.
View cameras, which focus the image onto a groundglass and have no viewfinder behind the lens, never incorporated TTL metering; large-format landscape and architecture photographers have always needed external meters of one sort or another. There are many reasons to continue to shoot film, either exclusively or with digital, and the tilt-shift movements and extreme fine detail of the view camera is one.
There are also many cameras out there with good or even great optics that either do not have built-in light meters or have selenium photovoltaic light meters which failed long ago due to corrosion or exposure to moisture. Among these are Leica rangefinders before the M5, early Contax cameras, folding medium-format cameras like Zeiss Super Ikontas and Voigtlander Bessas, and most TLR (twin-lens reflex) cameras including Rolleiflexes and Yashica-Mats. As long as film is being produced and processing is available, there's no good reason to not shoot with these cameras. Having to guess metering, however, can make the experience frustrating.
For those of us who never developed a knack for metering by eye, the inexpensive and easily portable Sekonic L-208 meter helps us give a second life to vintage cameras.
Impressions of the Sekonic L-208 Twinmate/Twinmaster
I've been using my Sekonic L-208 primarily with a Yashica-Mat 124G with some damage to the coupling in its built-in meter. Even if the built-in meter were working (it is repairable) an external meter also makes close-up shots with that camera--impossible to meter with the non-TTL built-in system--possible.
The Sekonic L-208 has also facilitated long-exposure shots with my 35-year-old Canon SLR, too dark for the built-in meter. Having an incident-light meter also comes in handy when the reflectance of the subject doesn't average to 12%--the hypothetical "black cat in a coal mine" or "ball bearing on a mirror"--eliminating some of the need for bracketing and "guess" compensation for such challenging shots.
Usage is easy and nearly intuitive for those already accustomed to match-needle metering. A sight of some sort would, however, be welcome; the precise region being measured when metering reflected light is not obvious--am I really pointing it where I think I'm pointing it?--and even a pop-up two-window viewfinder would help. Aside from that and a tendency for the film speed dial to drift while being handled, there are no usability flaws, and Sekonic's choice to alternate between red black in its numbering--standard practice on all of its analog meters--makes reading the L-208 meter at arm's length easy.
In a world where all displays seems to be becoming digital, Sekonic's match-needle system is welcome. Something about galvanoscope needles is cognitively easier than reading digits and watching them twitch back and forth--spatial relationships often work better than numbers. That's the reason we still use oscilloscopes even in the days of digital acquisition boards. I miss old analog multimeters and stereo amplifiers and radio tuners with needle gauges, even though I understand the limitations of analog meters for precision work. The match-needle system on the L-208 doesn't suffer from such problems: the scale spacing is such that exposures can be read to quite a bit more precision than the half-stop or third-stop adjustment available on most cameras.
Like any electro-mechanical device, the Sekonic L-208 is a bit fragile. Its plastic housing only feels flimsy, but the internals are perhaps damage-prone. I had to return mine for warranty service following what should have been a minor shock, which caused the device to work only intermittently and then only when banged very hard against my hand; something had likely come loose, rare in most such devices since surface-mounted components became prevalent. The service report indicated that the printed circuit board had to be repaired.
Followign its repair, the Sekonic L-208 has accompanied me on quite a few hikes and off-trail bushwhacking trips. However fragile it is, it isn't unusably fragile. II can't say that it's anything special; compared to Sekonic's own combination reflected/incident/zoom spot/flash meters it seems primitive. But it does what I purchased it to do, and unlike those meters, it's sold at a reasonable price, affordable to hobbyists like myself and inexpensive enough to take into the backcountry without worry about breaking or losing an instrument that costs a month's rent or more.