I haven't been able to find an answer on google.
I want to know the 35mm equivalent of my Hasselblad
lenses using a digital back. For simplicity sake, the crop
multiplier is 1:1 (full 645)
Anyone know?
You can work this out on the two dimensions of the format, or the diagonal (Pythagoras).
60mm * 45mm to 26 * 24mm or 40.4 * 53.7mm or whatever
Crop factor is nonsense...
In the real world what matters is the angle of view, (long, short or diagonal).
...and this is 2*arctan((d/2)/f)), where d is the long, short or diagonal dimension.
or, in ExcelSpeak =2*(DEGREES(ATAN((d/2)/f)))) In the table below, for cell B3 (87.5 degrees)
=2*(DEGREES(ATAN((B$2/2)/$A3))). The $ signs sort out the absolute and relative cell addresses, so the formula can be copied to all degree cells. (diagonal 67mm calculated form long and short by Pythagoras).
This does not necessarily agrees with the manufacturer's quoted specification for a lens, as they might be quoting fields of view for a different sensor size, or for the nominal (non-existent) 60mm * 45mm sensor size... and the actual focal length of a lens can be considerably different to the nominal, e.g. the Hasselblad 300 is actually 292mm.
Focal length | Long | short | Diagonal |
| 53.7 | 40.4 | 67.2 |
----------------- | ---------- | ---------- | ------ |
28 | 87.5 | 71.6 | 100.3 |
35 | 74.9 | 59.9 | 87.6 |
47 | 59.4 | 46.5 | 71.1 |
80 | 37.1 | 28.3 | 45.5 |
90 | 33.2 | 25.3 | 40.9 |
120 | 25.2 | 19.1 | 31.2 |
300 | 10.2 | 7.7 | 12.7 |