Understanding Medium Format vs 35mm Lenses and Equivalent Focal Lengths by James Baturin

Written by James Baturin

Making the switch from 35mm to medium format film involves a bit of an overhaul in the way you think about lens focal lengths.

For me, when suddenly a 50mm lens was considered “wide angle” and an 80mm lens was considered “true-to-life” it took some getting used to.

And since most people’s focal length frame of reference is from the 35mm point of view, knowing the medium format lens equivalent to popular 35mm lenses, and why there’s a difference in the first place, is really helpful if you’re looking to get into medium format photography.

Why Is There a Difference Between 35mm and Medium Format Lenses?

So why is there a difference?

Most simply put, with medium format film, the larger negative means a wider field of view. And the wider the field of view, the longer the focal length needed to produce an image equivalent to the (smaller) field of view on 35mm.

You can see how the size of a 35mm film negative compares to the different medium format negative ratios below.

Understanding Crop Factor

To calculate a medium format len’s 35mm equivalent, we can use something called “crop factor.”

It’s a number that can be used to compare the relative field of view of different medium format film aspect ratios to 35mm film.

It is calculated by dividing the diagonal length of a 35mm negative (43mm) by the diagonal length of whichever format you are comparing it to.

So for example, the crop factor for 645 medium format aspect ratio to 35mm is roughly 0.62 (43mm/69.7mm=0.62).

Taking the crop factor and multiplying it by the focal length of the medium format lens, then, will give you the rough 35mm equivalent.

For our 645 medium format lens then, an 80mm lens will give us roughly the same field of view as a 50mm lens on a 35mm camera (80×0.62=50).

It’s important to note that this equation isn’t exact, and will start to become less accurate the more the aspect ratios of the film differs from the standard 2:3 ratio of 35mm film.

However, for the practical purpose of figuring out a rough medium format equivalent for your favorite 35mm lenses, the crop factor number works just fine here.

Image Examples with Different Focal Lengths

Numbers are pretty abstract, so I’ll include some more tangible examples from the lenses I’m currently using with my Hasselblad 500 C/M.

With a 6×6 aspect ratio, the 80mm lens is considered the 50mm equivalent on 35mm. It’s the lens I use most often, as it gives me the field of view that’s closest to what the human eye sees, and it’s versatile for shooting any subject matter.

As a landscape photographer, a wide angle lens is a must have. I’ve got a 50mm lens that with my 6×6 camera works out to about a 28mm focal length on 35mm.

It’s a focal length that allows me to include a wide array of subject matter in my images, crucial for time I want to include foreground elements held against a more expansive middle and background.

The third lens that rounds out my kit is a 150mm lens, that works out to about 83mm on 35mm film.

This lens is a great portrait lens, as it reduces distortion of face shape due to a “flatter” field of view. It’s also a great lens for times when my 80mm just doesn’t get my subject large enough in the frame, and gives me just enough “zoom” to make it more prominent in my image.

35mm Equivalent for Different Medium Format Lenses

I’ve included some cheat sheet charts below with the crop factor for some common medium format aspect ratios, along with 35mm lens equivalents for different lenses (I’ve highlighted the focal lengths that are approximate 50mm equivalents on 35mm for each).

If there is a medium format lens I haven’t included, simply multiply the focal length by the crop factor to get the 35mm equivalent!

645 Crop Factor = 0.62

6×6 Crop Factor = 0.55

6×7 Crop Factor = 0.5

6×9 Crop Factor = 0.43

If you’re looking to make the jump from 35mm to medium format film, hopefully this helps when considering which lenses will work best for you, based on your knowledge of 35mm lenses!

Thank you so much, James! James is a regular contributor here at Shoot It With Film, and you can check out his other articles here, including A Multiple Exposure Experiment: 20+ Exposures in a Single Film Image and Double Exposure Hack for the Hasselblad 500 C/M.

You can also check out James’s work on Instagram.

Leave your questions about the differences between 35mm and medium format lenses below in the comments!

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James Baturin

James Baturin is a regular contributor for Shoot It With Film. Find his other articles here, including Hasselblad 500 C/M Film Camera Review and Long Exposure Film Photography Tutorial.

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