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The Phoblographer Answers: What Does the MM on a Lens Mean and Stand for?

Chris Gampat
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03/01/2018
2 Mins read
Chris Gampat The Phoblographer Lensbaby Velvet 85mm f1.8 product images 3

Last Updated on 03/03/2018 by Mark Beckenbach

If you’re into photography, you most likely know the answer to the question “What do the letters ‘mm’ on a lens stand for?” But for the uninitiated and for lots of Americans who don’t know the metric system or what millimeters are, it can be pretty confusing. I mean, we can understand that eight inches is larger than two inches, right? So bigger, must mean better, right? No, not exactly and that couldn’t be further from the truth.

Essentially, the wider the field of view, the smaller in focal length number. The more narrow (telephoto) views are larger in focal length numbers. So, a 14mm lens will give you a wider field of view than an 85mm lens. But then things become even more confusing as pretty much every standard of focal lengths are then more or less based off of 35mm film.

12mm (24mm)
100mm (200mm)

You see, there are things called crop factors–and they are created in regards to how much smaller or larger a sensor or film plane is to 35mm film. So on a Four Thirds sized sensor, there is a 2x crop factor. So a 12mm lens will give you the equivalent field of view of a 24mm lens on a full frame 35mm camera. But nonetheless, the standard stays the same. The smaller the number of millimeters, the wider the field of view and focal length. The larger the number, the more narrow it is.

But then consider the geekier side of it. what does the millimeter actually stand for. To put it simply, it stands for the distance between the back element of the lens and the camera’s sensor or film plane. With a zoom lens, you can expect that to change accordingly. With an option like a 24-105mm lens, the back element of the lens starts out at 24mm and as you zoom further into the subject (increased the millimeter numbers) you move the back element further away from the sensor and film plane. Part of this is why we call them “longer focal lengths” or “shorter focal lengths” because longer lenses need to be made, well, longer in order to accommodate the design.

Of course, it can get more complicated than this, but why worry?

camera crop factor focal length inches lens longer millimeters Photography shorter
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Chris Gampat is the Editor in Chief, Founder, and Publisher of the Phoblographer. He provides oversight to all of the daily tasks, including editorial, administrative, and advertising work. Chris's editorial work includes not only editing and scheduling articles but also writing them himself. He's the author of various product guides, educational pieces, product reviews, and interviews with photographers. He's fascinated by how photographers create, considering the fact that he's legally blind./ HIGHLIGHTS: Chris used to work in Men's lifestyle and tech. He's a veteran technology writer, editor, and reviewer with more than 15 years experience. He's also a Photographer that has had his share of bylines and viral projects like "Secret Order of the Slice." PAST BYLINES: Gear Patrol, PC Mag, Geek.com, Digital Photo Pro, Resource Magazine, Yahoo! News, Yahoo! Finance, IGN, PDN, and others. EXPERIENCE: Chris Gampat began working in tech and art journalism both in 2008. He started at PCMag, Magnum Photos, and Geek.com. He founded the Phoblographer in 2009 after working at places like PDN and Photography Bay. He left his day job as the Social Media Content Developer at B&H Photo in the early 2010s. Since then, he's evolved as a publisher using AI ethically, coming up with ethical ways to bring in affiliate income, and preaching the word of diversity in the photo industry. His background and work has spread to non-profits like American Photographic Arts where he's done work to get photographers various benefits. His skills are in SEO, app development, content planning, ethics management, photography, Wordpress, and other things. EDUCATION: Chris graduated Magna Cum Laude from Adelphi University with a degree in Communications in Journalism in 2009. Since then, he's learned and adapted to various things in the fields of social media, SEO, app development, e-commerce development, HTML, etc. FAVORITE SUBJECT TO PHOTOGRAPH: Chris enjoys creating conceptual work that makes people stare at his photos. But he doesn't get to do much of this because of the high demand of photography content. / BEST PHOTOGRAPHY TIP: Don't do it in post-production when you can do it in-camera.
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