How do you measure your lens?

[Huck Finn]

After reading about the new Zeiss Ikon line on the internet, I noticed that Zeiss lists longer physical lengths for their lenses than Leica does for corresponding focal lengths in their specs. But when I went to PhotoPlus Expo in New York, I didn't notice much of a difference in most of the lenses that I saw.

So, I measured one of the ZI lenses at the expo. When I got home, I checked the ZI website. My measurements of the full length of the lens from bottom of the lens mount to front glass were the same. However, when I measured my Leica lens, the length from the Leica specs corresponded only to the portion of the lens that protrudes from the camera body, i.e. it didn't include the lens mount. I may have made an error in measurement, but I don't think so.

Oddly, when I measured my Voigtlander 75/2.5, it didn't correspond to either of the 2 measurements. The CV spec matched only the length of the lens protruding from the camera body (i.e. exclusive of lens mount like Leica) but with the lens hood attached.

I'm posting this to get a fact check from you folks & to see if anyone knows about the general industry practice in this respect. This seems like an important piece of information when making a purchasing decision especially if you're not in a position to look at 2 lenses side by side. Many of us value the compact size of our RF lenses, so accurate information is important.

Thanks for the help.

[Doug]

Interesting observation, Huck. In my view, the important measurements are how far the lens protrudes from the camera body at infinity with and without hood, and perhaps also how far it projects inward toward the shutter if that's by a significant amount. That last might be getting more imiportant these days as a rough guide to its suitability for digital sensors...?

I agree that published measurements should either adhere to some agreed method (preferably), or specify the method used.

[Brian Sweeney]

It doesn't matter how I measure them; every time the RF's see that Nikon 500mm F4 AF-S they feel inadequate.

[mikeb380]

Huck, are you talking about focal length or about physical length of the lens. If physical, the only guide you have is to measure them yourself, there is no standard on that. If it is physical length, there can't be a large variance as the focal length is from the optical center of the front element to the film/sensor plane. Of course some lenses have extra added on, I guess as a lens hood. My 200mm for my EXA has about 2 inches protruding and not collapsible.
Michael