It’s rare to come across series-size filters today. They’re mostly relegated to the vintage category.
It refers to an older photography filter system, mostly used in the mid-20th century up to around the 1970s. But if you’re using a vintage manual-focus lens, you might run into the term.
The term “series size” refers to a system to standardize filter sizes for camera lenses. Unlike today’s modern lenses, which commonly use threaded filters that screw directly onto the lens’s front element, many older lenses use a slip-on filter system.
Series filters look very much like the kind of threaded screw-on filters that are common today, but there are some key differences.
Attaching Series-Size Filters
For one, series-size filters don’t have threads. So they can’t attach directly to the lens (this was at a time when lenses often didn’t have threads). And that means there needs to be a different way to hold the filter in place. The solution is to sandwich them in place.
For that reason, there are three parts to the system.
- A metal adapter ring slips onto the end of the lens barrel.
- The filter itself slides into the metal adapter ring.
- A retaining ring slides over the filter and attaches to the adapter ring, locking the filter in place.
Series Filter Sizing
The “series” part refers to the sizing. And it means that a single filter might be usable on lenses with different diameters so long as you switch out the adapter ring. So, it’s conceptually the same as using a step-down or step-up filter ring.
Each series corresponds to a range of lens diameters.
|Series Number||Approx. millimeter range|
|5||28 – 36|
|6||31 – 47|
|7||44 – 56|
|8||51 – 69|
|9||62 – 85|
As a practical example, a lens might require a Series 9, 82mm adapter ring. That adapter ring would accept any Series 9 filter like the one in the photo I’ve included at the top of this page.
Pros & Cons of the Series Size Filter System
The biggest disadvantage of the system is that it’s quite cumbersome, requiring three pieces to be fiddling with.
And to stack filters, you need to add additional retaining rings.
But the biggest advantage of the system is its flexibility. It’s still not as flexible as a newer style of filter holder system. But the series-size system allowed you to keep a fairly standard selection of filters that could be used on different diameter lenses simply by switching out the adapter.
Once upon a time, they were also cheaper. But that’s no longer the case, as series-size filters fell out of favor half a century ago and became vintage gear while replaced by a flood of threaded direct-attach screw-on filters.
Parting Words from KODAK
I was amused by Kodak’s take 1 on series-size filters:
Although series-size filters are usually cheaper than direct-fitting filters, they do have a drawback. That drawback comes under storage and retrieval. Finding the needed pieces can take as much time as looking for last year’s Christmas decorations. When the sun is dipping below the horizon, and you’ve found the orange filter and the retaining ring but can’t find the appropriate adapter which has burrowed into the bottom of your camera bag, you might not relish your series-size filters any more. If you’re neat and orderly, no problem. If you aren’t, beware.
- The KODAK Workshop Series: Using Filters, revised edition (New York: Silver Pixel Press, 2000) p.15.