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.
Right: 35mm film camera, the Nikon FE
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.
Related: 35mm vs 120: Choosing a Film Format
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
| 645 Lens | 35mm Lens Equivalent |
|---|---|
| 45mm | 28mm |
| 55mm | 34mm |
| 60mm | 37mm |
| 80mm | 50mm |
| 100mm | 62mm |
| 120mm | 75mm |
| 150mm | 93mm |
| 200mm | 124mm |
6×6 Crop Factor = 0.55
| 6×6 Lens | 35mm Lens Equivalent |
|---|---|
| 40mm | 22mm |
| 50mm | 28mm |
| 60mm | 33mm |
| 80mm | 44mm |
| 120mm | 66mm |
| 150mm | 83mm |
| 180mm | 99mm |
| 200mm | 110mm |
6×7 Crop Factor = 0.5
| 6×7 Lens | 35mm Lens Equivalent |
|---|---|
| 45mm | 23mm |
| 50mm | 25mm |
| 65mm | 33mm |
| 90mm | 45mm |
| 105mm | 53mm |
| 180mm | 90mm |
| 200mm | 100mm |
| 250mm | 125mm |
6×9 Crop Factor = 0.43
| 6×9 Lens | 35mm Lens Equivalent |
|---|---|
| 65mm | 28mm |
| 90mm | 39mm |
| 100mm | 43mm |
| 105mm | 45mm |
| 150mm | 65mm |
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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Blog Comments
David Kaftal
June 13, 2022 at 9:11 pm
I noticed that you give exactly the same crop factor for 6×6 and 6×7, although the focal length equivalents are different. I’m wondering if that’s a typo.
shootitwithfilm
June 13, 2022 at 10:45 pm
Yes, it was a typo! Thank you! The crop factor for 6×6 is 0.55, and the crop factor for 6×7 is 0.5. We corrected it in the article.
AP
October 3, 2022 at 6:12 pm
Great article but the crop factors don’t match the actual calculations. The diagonal of 6×6 negative is about 84.85mm. Shouldn’t the crop factor be 0.51 (43.27mm / 84.85mm)? Similarly, the crop factor for 6×4.5 be 0.58 (43.27mm / 75mm)?
shootitwithfilm
October 3, 2022 at 10:08 pm
Hi AP! 6×6 negatives are typically 56mm on each side, not 60mm. That’s why your calculations are slightly different. Similar to 645 format. Those negatives are most commonly 56mm x 41.5mm. Hope this helps!
AP
October 4, 2022 at 12:29 pm
Thank you for the clarification. The crop factor charts on the article are very helpful.
Harry
October 3, 2022 at 11:30 pm
The crop factor calculations aren’t correct because you must compare the actual length of the diagonal of each format, not just their ratio. For eg. for 645: the diagonal is the square root of [(6cm X 6cm) + (4.5 cm X 4.5 cm)]. This means the diagonal of a 645 negative is approx 75mm. So the crop factor is 74mm/43mm or 1.74. So a 50mm lens would be about 87mm in 645. Hope this helps.
Michael D Cadogan
October 15, 2022 at 8:50 pm
You did not say what is the 35mm equivalent to the Hasselblad 500 mm Lens.
Vic
January 3, 2023 at 10:08 am
I’m glad you mentioned how aspect ratio affects the accuracy of a crop factor. While crop factor gets you in the ballpark, when going from a 35mm aspect ratio to a 4×5 (Hasselblad X1D) the lens “equivalent” isn’t as wide after using the calculation. What should I do to know how wide I can expect to go when shooting landscape, for example? Thank you!
Daniel St Louis
February 19, 2023 at 11:36 am
Unfortunately this is another instance of confusing comments regarding comparing lens focal lengths between image sizes. The basis for comparison is not the dimensions of a particular format but the full square image size the crop format is based on. Lenses project a CIRCLE of illumination not an OVAL of illumination. This means for equivalent perspective we compare a 56mm square image for 6X6 to a 36mm square image for 35mm. The corner to corner distance of the square image is related to the diameter of the image circle so using just a part of that does not alter perspective. Only the longest side is important. Calculations yield fairly close results when dealing with shorter focal lengths but become quite skewed at portrait length and longer.
645 and 6X6 both use a factor of 0.63. 6X7 has a long side of 72mm. Nominal 6X8 and 6X9 images vary a little for individual cameras and have a long side 3 or 4 mms shorter than stated size.
Michael Elliott
June 9, 2023 at 11:03 am
Ah this old chestnut again.
Whack a lens on, look through the VF and see if it frames what you need in the way you need it.
If it doesn’t, whack a new lens on.
If it does, keep in mind the focal length that gets you where you want to be.
Rinse and repeat until you know for you what you need to use to do what you want to.
It’s easy enough to split the lenses into ultrawides, wides, normals, short teles and long teles.
Yes crop factor is helpful but actually putting the damn thing up to your eye and looking is more helpful.
David Murray
August 7, 2023 at 7:42 am
Thank you for your most incisive response.
Zong Liu
October 5, 2023 at 12:18 pm
This method is only to be used to estimate the area of the lens coverage. It is not accurate and vary from camera model to camera model. I have a 40mm Hasselblad Carl Zeiss lens and it is equivalent to 28mm, not 24mm. I just simply compare my medium format lenses to 35mm lenses and find out the medium format lenses’ equivalent number.
Another important issue I think is perspective. The perspective depends on the focal length of the lens. The perspective of a 150mm medium lens is totally different from the perspective of its 35mm equivalent even though it covers the same area of 90mm 35mm lens. The pictures from medium format lens are more compressed with shallower depth of field.
Brett Rogers
October 29, 2023 at 8:41 am
Perspective is determined by the distance from one’s subject, not by the focal length. You might need to be at different distances to achieve the same subject framing using both medium format and 35mm cameras (depending, of course, on the lenses fitted to each) however it is the subject distance which impacts the perspective, not the focal length.
This is fairly easy to prove by taking images focused to the same distance with different focal length lenses, from an identical camera position. Crop the image made with the shorter lens, until it matches the full frame of the image made with the longer lens, and…the subject perspective will be identical.