I have an older Olympus OM 50mm lens that I'd like to get a matte box for, as I'm going to use it for video on a 550D. However, I can't seem to figure out what the thread diameter is. There are no markings on the lens itself to indicate what diameter. How do I figure this out?

Here's the lens I have. It's the standard 50mm ƒ/1.8 kit lens that came with many Olympus OM lenses in the '80s

  • A quick google search shows that it's a 49mm thread – camflan Sep 10 '12 at 18:45


It never fails to research the lens and read the specs online. And there will be no room for mistake there:

Olympus 50mm 1.8

Look for 'filter size', naturally.

  • Ah. I guess I wasn't paying attention to filter size. I was looking for thread something or the other. I'm still somewhat new to the DSLR world, so thanks for that helpful info!! – daviesgeek Sep 10 '12 at 19:13
  • That's what I thought when I saw the image you attached, which most likely came from the same website I linked. – Jakub Kaleta Sep 10 '12 at 19:39
  • It was from the same site, I'm pretty sure...anyhow, I appreciate your help, even though it was just pointing me in the right direction. :-) – daviesgeek Sep 11 '12 at 5:27

Have you considered using a ruler? There are 2-3 millimeters (or more, in the larger sizes) between standard filter thread diameters. Simply measuring across the filter thread will give you a diameter that's just about 1mm less than the actual thread size, so if you measure 48-and-a-bit millimeters, your lens takes a 49mm filter; 51-and-a-bit takes a 52mm, and so on. You don't have to get a micrometrically-perfect measurement, since there are no odd fractional values to worry about for standard filters.

  • Actually, there are lenses currently in production with 41mm, 40.5mm and 39mm thread-sizes. Yes, two of those are ½mm apart :( – Itai Sep 10 '12 at 19:02

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