How does a 150mm f/4 Hasselblad medium-format lens behave on a full-frame 35mm camera?
Asked 6/2/2015
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I’m adapting a Hasselblad Sonnar C 150mm f/4, originally made for 6x6 medium format, to a full-frame 35mm camera. How do I work out the new angle of view and any “equivalent focal length”? Does the f/4 aperture change when the lens is used on a smaller sensor, or does only the field of view change?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
11y ago
2 Answers
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A 150/4 on 35mm acts like a 150/4 on 35mm.
Full-frame 35mm (43.2mm diagonal) is the default frame of reference. Equivalence is usually about referring some other sensor/film size back to that 35mm default. As in "if I use X on my camera it'll be like using Y on FF 35mm."
But... the math in case you do care about the other equivalences:
Diagonals are more accurate than long edges when comparing formats of different shapes, so I'll use the 43.2mm diagonal of 35mm vs. the 79.2mm diagonal of the 56mm x 56mm—aka 6x6—'Blad.
On that 6x6 this lens had a 35mm equiv. focal length of (43.2mm/79.2mm * 150mm) = 82mm and an equivalent aperture of f2.2.
To go the other way just flip the math around (79.2/43.2 * 150)=275mm and f7.3. So using it on FF is like using 275/7.3 on a 'Blad.
Originally by user40265. Source · Licensed CC BY-SA 4.0
user40265
11y ago
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Generated from our catalog & community — verify before relying on it.
The lens itself does not change: it remains a 150mm f/4 lens.
On a full-frame 35mm camera, only the sensor size changes, so you use a smaller portion of the lens’s image circle. That gives a narrower field of view than it had on 6x6 medium format.
Using diagonal comparison, 6x6 is about 79.2mm diagonal and full frame is about 43.2mm, so the crop factor from 6x6 to full frame is about 79.2 / 43.2 ≈ 1.8x.
So your 150mm on full frame gives roughly the same angle of view as a 275mm lens would on 6x6. In other words, it will feel much more telephoto than it did on the Hasselblad body.
The f-number does not become f/2. It stays f/4 for exposure. If you compare depth of field and total-image “equivalence” back to 6x6, then 150mm f/4 on full frame is roughly similar to about 275mm f/7.3 on 6x6.
So the practical answer is:
- actual focal length: 150mm
- actual aperture: f/4
- narrower field of view on full frame
- about 275mm equivalent when compared back to 6x6 medium format
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