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Crop factor on 36.7 x 49 mm CCD sensor

HenryFool

Member
Can anyone tell me what the crop factor equivalents for a 36.7 x 49 mm CCD sensor (CFV39) would be:

For example:
If the 35mm equivalent of a Hasselblad 80mm MF lens is roughly similar to 50mm, what is the 35mm equivalent of the 80mm lens using a CFV39 (36.7 x 49 mm sensor)?

Math is not my forte, so any equations will be lost on me! and while I do grasp the concept that the answers vary on whether you are using diagonals based on either 1:1 or 4:3 formats I'm hoping to get a rough equivalent

Thanks 🙂
 

FloatingLens

Well-known member
Yes, for P45 on Contax 645 the Zeiss Distagon 55 becomes sort of the standard lens. For a square sensor 37x37, a 50mm lens would take that role.
 

Godfrey

Well-known member
Can anyone tell me what the crop factor equivalents for a 36.7 x 49 mm CCD sensor (CFV39) would be:

For example:
If the 35mm equivalent of a Hasselblad 80mm MF lens is roughly similar to 50mm, what is the 35mm equivalent of the 80mm lens using a CFV39 (36.7 x 49 mm sensor)?

Math is not my forte, so any equations will be lost on me! and while I do grasp the concept that the answers vary on whether you are using diagonals based on either 1:1 or 4:3 formats I'm hoping to get a rough equivalent

Thanks 🙂
You can use an online FoV calculator (like this one: Rui Salgueiro's field-of-view calculator) to input a standard format and a range of focal lengths, generate a listing of the H, V, and D angles, and then change the input to whatever format you want to assess equivalences for, a range of focal lengths, and output a suitable listing for them. Then you just compare the angles for like-format proportions to find equivalents.

G
 

rdeloe

Active member
Another quick approach is to compare (focal length) / (Image length). When they're the same, the angle of view is the same. "Image length" can be horizontal, vertical or diagonal.

To illustrate,
  • 50mm lens on 36mm edge of a 24mm x 36mm sensor is 1.389 (50/36)
  • 61mm lens on 44mm edge of a 33mm x 44mm sensor is 1.386 (61/44)
Comparing sensors with different aspect ratios (e.g., above) is a bit dubious. There's not one "crop factor" in those cases -- you need to settle on long edge or short edge. I never use diagonal for that reason. I generally use the short edge when I bother doing this.
 

Godfrey

Well-known member
That looks impressive but it's way over my head o_O
Is not too difficult with Rui Salguerio's "Angle of View" calculator.
- Input a set of focal lengths
- Select a standard 6x6 format .. say "50 80 120 150"
- press the "Submit Request" button to get a list

Width = 56 mm, Length = 56 mm, Diagonal = 79.196 mm
f Hor Vert Diag H/V
50.0 58.4977 58.4977 76.7556 1.0000
80.0 38.5801 38.5801 52.6685 1.0000
120.0 26.2680 26.2680 36.5240 1.0000
150.0 21.1470 21.1470 29.5759 1.0000


That list is the Angle of View set for those focal lengths on a Hasselblad with A12 magazine. Now go back to the previous page and
- click the button for Pentax 645 (33x44mm) format (same as the Hasselblad 907x or X1D)
- make the focal length list "21 30 45 50 65 80 120 135 150" this time, to show both the V system and a set of X system lenses.
- press the Submit Request button to get a new list

Width = 33 mm, Length = 44 mm, Diagonal = 55 mm
f Hor Vert Diag H/V
21.0 92.6644 76.3145 105.2667 1.2142
30.0 72.5077 57.6216 85.0209 1.2583
45.0 52.1070 40.2726 62.8591 1.2939
50.0 47.4990 36.5258 57.6216 1.3004
65.0 37.3980 28.4869 45.8642 1.3128
80.0 30.7525 23.3077 37.9408 1.3194
120.0 20.7777 15.6582 25.8148 1.3270
135.0 18.5115 13.9365 23.0277 1.3283
150.0 16.6878 12.5546 20.7777 1.3292


You can see from the bolded items in the two lists that the horizontal angle of view with an 80mm lens on 6x6 is about the same as the horizontal angle of view with a 65mm lens on 33x44. And the same is true of 150mm on 6x6 vs 120mm on 33x44. So the "crop factor" when going from a Hasselblad square format lens to an X1D lens is about 0.8x to get the same FoV.

You can do the same thing for 35mm FF format as well. Using a commonly available set of focal lengths in 35mm:

Width = 24 mm, Length = 36 mm, Diagonal = 43.2666 mm
f Hor Vert Diag H/V
24.0 73.7398 53.1301 84.0622 1.3879
28.0 65.4705 46.3972 75.3806 1.4111
35.0 54.4322 37.8493 63.4400 1.4381
50.0 39.5978 26.9915 46.7930 1.4670
75.0 26.9915 18.1806 32.1798 1.4846
90.0 22.6199 15.1893 27.0316 1.4892
100.0 20.4079 13.6855 24.4137 1.4912
135.0 15.1893 10.1592 18.2081 1.4951


The closest match to a 35FF 50mm normal lens for the Hasselblad is a 65mm lens, and the closest match to a 35FF 100mm portrait lens is a 120mm lens on the Hasselblad. That's a crop factor from 35FF to 33x44 format of 1.23x.

As rdeloe does, I only compare the horizontal angle of view since the format proportions are different between A12, X system, and 35FF. Once you start trying to calculate in the different format proportions, it gets a bit complicated so I don't bother... The whole point is simply to have a rule of thumb for approximate equivalent focal lengths. Different format proportions present differently ...

G
 
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HenryFool

Member
@Godfrey thank you so much for taking the time to explain that so well - I could have done with a math teacher that had your eloquence and clarity!
 

Godfrey

Well-known member
You're welcome.
BTW: The tool also has a pre-packaged selection for the CFV39 format, same as the H5D-50. Using the 80mm lens you mentioned, the calculated FoV is:

Width = 36.8 mm, Length = 49.1 mm, Diagonal = 61.36 mm
f Hor Vert Diag H/V
80.0 34.1199 25.9055 41.9636 1.3171


Comparing the Horizontal FoV to a calculation for 35FF and the range of lenses from 45 to 60 mm ...

Width = 24 mm, Length = 36 mm, Diagonal = 43.2666 mm
f Hor Vert Diag H/V
45.0 43.6028 29.8628 51.3509 1.4601
50.0 39.5978 26.9915 46.7930 1.4670
55.0 36.2437 24.6160 42.9427 1.4724
60.0 33.3985 22.6199 39.6541 1.4765


It appears that a 60mm lens is about right, netting a 1.3x crop factor from 35FF to CFV39 format. Example: If you want the equivalent of a 35FF 100mm lens on your CFV39, you'll need about a 135mm lens. The calculations for 35FF/100mm and CFV39/135mm using the tool confirm this.

35FF ...
Width = 24 mm, Length = 36 mm, Diagonal = 43.2666 mm
f Hor Vert Diag H/V
100.0 20.4079 13.6855 24.4137 1.4912


... to CFV39
Width = 36.8 mm, Length = 49.1 mm, Diagonal = 61.36 mm
f Hor Vert Diag H/V
135.0 20.6134 15.5228 25.6071 1.3279


best,
G
 
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