27mm filter isn't 27mm? Contaflex filter...

I just got a modern voigtlander 50mm f3.5 and was ficking up a couple of 27mm B&W contrast filters for it. I bought one off ebay that the ad said "27mm", the side of the filter has 27mm stamped on it but it measures 25mm. It was marketed for a contaflex, did they use a different ruler from the rest of us? lol

Now I'm concerned that all these vintage 27mm filters might be some odd ball thing for the contaflex's where they are marked 27 but are actually 25. Anyone else ever run into this?

Stephen, old filters markings can be strange. Recently I encounter that Retina's filters are marked as 32mm but they are actually 29.5mm? https://filterfind.net/Index.html is great resource for old filters

If you carefully measure, I'll bet you will find that the indicated size is actually a measurement of the exterior size of the filter - relevant to hood sizes and other similar issues.
Retina filters are usually Series filters - intended usually to be used with Series adapters. It may be the same with Contaflex.

For the Retina- the Kodak Retina filters are marked 32mm, and tend to be very flat to allow the filter to remain on the camera as you fold it. The Retina hood is a push-on. The actual filter thread is 29.5mm.

I just checked my Zeiss Tessar 5cm F2.8. I used the front element of a very-broken Contaflex to repair a Tessar in Contax mount: 25.5mm screw in. I just tried to screw in the Zeiss Stuttgart "27" filter into it- it's too big. I measured the threads with digital calipers, came out very close to 27mm. I also have a Kenko filter marked "27" diameter, and the Zeiss filter screws into it. Another Zeiss marked S27 screwed into my Telesor 27mm (marked 27mm) filter prefectly. Three filters from three different manufacturers agree, all screw into each other.

Glad I looked- found some unmarked Sigma filters that fit my Industar-50 collapsible perfectly, measure 22mm.

The thread pitch of the filter is also important- filters of the same diameter may have 0.5mm, 0.75mm, or other pitch to the threads. These are not compatible.

I use the Zeiss 27mm filters with several Nikkor wide-angle lenses that have inner filter rings, easier to find than 34.5mm.

__Brian said:

The thread pitch of the filter is also important- filters of the same diameter may have 0.5mm, 0.75mm, or other pitch to the threads.

Click to expand...

These cases though seem to be very rare. Heliopan with their wide range of thread sizes do not offer even one thread-diameter with two pitches.


I just had a problem with three KMZ fliters. All the same model, seemingly from one set. One male thread did not fit the other. It turned out that this one had slighthy larger diameter than the others. A tiny bit of circumpherical grinding made it fit the others.

I have an old Contaflex, and had a Rollei 35 with the Tessar lens. They shared a screw-in hood, and my best hood left me on the Rollei when I sold it, much to my chagrin. That was a 24mm thread, according to the Googlez. My Contaflex is the Prima model, with the Pantar lenses. If you have the Tessar model Contaflex, it may be a different story.