Why 105mm?

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JasonTheBirder
JasonTheBirder Senior Member • Posts: 3,887
Why 105mm?
5

I guess there might not be a valid explanation but I wonder why so many lenses are 105mm when they could just be 100mm. I mean humans have a tendency to choose nice, round numbers, so I don't understand why lens designers chose to tack on an extra 5mm.

For smaller focal lengths like 17mm, it makes sense that there are 15, 16, 17mm because squeezing every extra mm wide makes a huge difference in the field of view.

But 105/100 = 1.05, hardly a big difference. I realize sometimes lens makers might go for something unusual for some reason like the Pentax 77 limited.

However, it seems that more than one manufacturer has chosen 105mm rather than 100mm:

  1. Nikon 105mm f/1.4
  2. Sigma 105mm f/2.8 macro
  3. Sigma 105mm f/1.4 art
  4. Venus Laowa 105mm STF
  5. Nikon Z 105mm f/2.8 macro

So what's so special about 105mm? Is it something historical? I tried searching on the internet and couldn't find anything. I guess there is also the 24-105 zooms too...

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