A photographer could lead a long and happy life never using filters at all. But eventually, many of us find we need a bit of color correction when shooting slide film, or want to try a red filter to give more drama to sky and clouds when shooting B&W.
Nowadays when you shop for filters and other lens accessories, it’s universal for their sizes to be listed in millimeters—reflecting the influence of metric-speaking Japanese and German optics manufacturers.
Yet if you flip through 50-year-old photo magazines, or root through the odd-parts bins at a vintage camera sale, you’ll start seeing accessories cryptically labeled Series V, Series VI, Series VII, etc. What are these weird sizes, and are they good for anything?
A Series filter has three parts: An adapter to fit the lens; a standard filter disk; and a retaining ring
“Series” adapters were the most common American system for lens accessories in the middle decades of the 20th century. And they were actually a very cool, totally modular way of doing things. My googling has not turned up much history about Series accessories. So I’ll share the information I’ve been able to put together—but I’d be grateful to hear from anyone who can steer me towards a definitive source.
My suspicion is that (as with many other photographic standards) it was Eastman Kodak who established the Series system. In any event, Kodak became a major supplier of Series filters and accessories.
The idea of the system was this: Colored filters, close-up lenses, etc., were manufactured in a few standard diameters—as “drop-in” disks, without threads. You chose the Series that would cover your largest diameter lens. Then, a multitude of different adapter rings were available, sized to fit all your various cameras and lenses.
Each particular Series had one standard-sized retaining ring, to hold the filter disk into the adapter. Some retaining rings had both male and female threads, allowing you to stack additional filters. Conveniently, the retaining ring could also be replaced with a lens shade having the same standard Series thread.
Mixing and matching modular parts. At right, a Series-threaded lens shade; can also be used without a filter
A few manufacturers put threads on their lens barrels that were “natively” standard Series sizes—thus no adapter was needed, just the retaining ring. Several Argus, Kodak and rangefinder Canon lenses adopted this system (and no doubt other brands I haven’t come across yet).
The dimensions of the system were specified in inches, not millimeters (this may resolve some mysteries you have with weird unidentified lens or filter threads). The different Series sizes were designated with roman numerals, and ranged from quite tiny (e.g. for cine lenses) up to moderately large. But Series V, VI, and VII seem to be the most common (and useful) sizes.
I measure their dimensions as:
Series V — filters 1-3/16″ (~30mm) — retaining thread 1-1/4″ (~32mm)
Series VI — filters 1-5/8″ (~41mm) — retaining thread 1-3/4″ (~44mm)
Series VII — filters 2″ (~51mm) — retaining thread 2-1/8″ (~54mm)
Series adapters to fit different lenses: TLR-style bayonet mount, unthreaded push-on, and threaded styles
Colored filters in Series sizes were available from many manufacturers—both names that will be familiar (like Tiffen) to others that faded away decades ago (like Omag). Some useful black and white filters might be found under unfamiliar, older color designations, such as deep red (formerly designated “A” but now #25), green (formerly G, now #13), and yellow (K2, now #8, or X1, now #11).
Kodak sold “Portra” close-up lenses in the common Series sizes, in strengths of +1, +2, and +3 diopters; but with non-reflex cameras you need a table of corrections to find the distance for proper focus. It’s nicest to get Porta lenses together with their original yellow Kodak containers, which include the table as a handy decal inside the lid.
Among the other Series oddities you sometimes see are Kodak’s “Telek” attachments: These were lenses with negative diopter powers. While it’s a bit non-intuitive, adding one in front of a lens and then racking its focus outwards has the effect of lengthening its effective focal length—yielding a quick & dirty telephoto lens. (The strongest -4 Telek can almost double the focal length). Unfortunately these are really only practical for cameras offering groundglass focusing, e.g. a Press camera.
Now, for most of my photographic youth, I used Japanese SLR systems, whose manufacturers tried to stick with a single filter diameter across most of their lens lines. For Olympus, it was 49mm; for Canon, 55mm. You just bought a couple of filters in the right size, and were done with it.
But, as my fascination with vintage cameras grew, somehow more and more of them began appearing in my home. And I had a problem—it seemed that each one used a different filter size!
But this is exactly the situation where the Series system shines. A friend had inherited a garage-ful of assorted series adapters and accessories; and by sifting through his heap, I was able to find adapters for about nine of my favorite vintage camera lenses—allowing me to use a single set of Series VI filters for everything.
Okay, I admit you could approximate the same thing today with one set of (oversized) threaded filters plus an arsenal of different step-up rings. But another advantage of the Series system is that many “slip-on” adapters were sold—making it possible to use accessories even on lenses that have no filter threads. (Or, ones with damaged threads, or impossible-to-find sizes… ) One Kodak 42mm push-on adapter turns out to be a perfect fit on vintage Diana cameras.
Slip-on Series adapters let you use filters with threadless oddball cameras
Admittedly, one place where this clever scheme falls apart is with polarizing filters. A polarizer needs to be rotated to a particular angle to be most effective, something that wasn’t practical with the Series drop-in disks. (In fact, there were clever threaded polarizing attachments manufactured for the Series system—you looked through a separate auxiliary polarizer while rotating a control handle—but it may be tough finding one today.)
It’s been decades since Series accessories were being widely produced. Yet if you dig around on eBay you will still find sellers offering series adapter rings and drop-in filters. (Note that some listings use Series 6, Series 7, etc., instead of the roman numerals.) Also, some specialist mail-order firms may be able to help.
If you need to track down every little odd Series filter component one at a time, the process might not be worth the effort. But if someday you’re as lucky as I was, and stumble onto some vast forgotten cache of Series accessories, just remember—it’s a neat system that’s still completely useful today.