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Lens factor CFV vs 6*6 or...???

E

eksund

Member
Hi out there!

I don´t understand how the official lens factor can be 1,1.

If I look at the spec for CFV-39 and CFV-50, Hasselblad is saying that the lens factor is 1,1.

With my own calculation (hypotenuse) I get the lens factor almost 1,4 compared with the 6*6 format.

The size of the sensor is 36,7 * 49,0 mm on the CFV:s backs and the film is almost 60 * 60 mm.

Can anyone bring some clarity in this matter?
 
That's realy not true.
Horizontaly the cfv is 49 instead of 56 that means 1.14x
Verticaly the cfv is 36,7 instead of 56 that means 1.52x
If you calculate in squar: 1.74 crop factor !
With film I was happy with a 65 /150mm now with my 50mm it's just too long for landscape.
BTW the Hasselblad V is not funny for vertical shot.Last time in studio for portrait with white paper, I noticed that I waisted 60% of pixels as I keep the body verticaly.
 
Result is then...

Hypotenuse = 1,29x
Vertical = 1,52x
Horizontal = 1,14x

Add that up and divide by 3 = 1,32x

So I think we can agree then on a factor appr. 1,3 instead of the official 1,1

Anybody against?
 
Mathematically speaking, It's the first time that I see a comparison between 2 triangles based on the average of the 3 sides. Since Pytagorus we could assume that the hypothenuse is already sort of "an avearge" :).

We could also compare the sensors on their surface ratio (1.6). But I assume that the 1.1 from Hasselblad is based on the ratio between the longest sides (56 versus 49). That makes sense as the majority of the MF pictures have always been resized on rectangular print.

For me the cropping factor must be looked at, keeping in mind the range of the lenses at the photographer disposal. My set of 40, 50, 60, 80, 100, 150 & 250 becomes 44,55,66 .... in landscape and 60, 75, 90, 120, 150, 220, 370 for my few "squares". What could be best ?

Add to that the fact that the 3 & 10 mm "off" on the border will cut the residual vigneting and we can hope an almost perfect system (even for the 40 mm which is defectless 32mm around its center.

Just changing the back of my old M6 Leica for a 19MP M9, made my small format prints as good as my hassys (13*17 on Epson 3880).

I'm saving Euro by Euro to make the jump.
 
Diagonals to compare

One has to calculate the diagonal for each of the rectangular formats. In digital the reference is film 6x45 (actually 56x41.5 mm).

Diagonal calculation is the square root of the sum of the length to the power of two and the with to the power of two.

Diagonal of:
56 x 41.5 = 69.7 mm
36.7 x 49.1 = 61.3 mm (CFV-39)
Crop factor: 69.7/61.3 = 1.137

Diagonal of:
56 x 56 = 79.2 mm
36.7 x 36.7 = 51.9 mm (CFV-39 in square mode)
Crop factor: 79.2/51.9 = 1.526

Hope this clarifies. So what Hasselblad reports is very correct.
 
First of all 6X6 (cm) is effectively 56X56 mm
6X4.5 is effectively 56X41 mm

That gives a crop factor for the CFV 39 of 1.1 refered to 645

Please note all crop factors from Hasselblad are refered to 645 format.
 
There is a Hasselblad V fit full frame 6x4.5 back from Phase One that also can rotate for Portrait images. Not cheap though!
 
Ed Bray said:
There is a Hasselblad V fit full frame 6x4.5 back from Phase One that also can rotate for Portrait images. Not cheap though!
Click to expand...


It is the LEAF APTUS - II 10 R or 12 R . R stands for rotation . Both also available with V-Mount .
 
Well, well, well....

.. you learn something everyday.
I did not know that Hasselblad compared with the 6*4,5.
Now it make sense.
Thank You for telling me.
 
eksund said:
I did not know that Hasselblad compared with the 6*4,5.
Now it make sense.
Click to expand...


A pity Hasselblad seems to have forgotten the 6x6 format.
The company got its excellent reputation from 6x6 cameras.

In the digital world there is no need for sensors larger than 6x4.5 or 56x41 mm.
 
Formats: square vs rectangles...

I think I understand how and why we got to the place we are at. In a general sense, prints are rectangles, almost always (though squares do occur). But if the ultimate goal is a print, then having a rectangular sensor does make some sense. There is no point in capturing data that you're not going to use. In this fashion, those digital back makers that allow swapping the back from horizontal to vertical are probably onto something, you're always capturing the image you need.
While I too lament the slow demise of square formats, I can see the logic pushing us towards rectangular capture. And in that case, comparing sensor sizes to 645 also makes some sense. So factors of 1.1 and 1.3 are approximately correct. Only the "small" square sensors are correctly compared to 6x6 with lens factors of just under 1.5.
[A final thought: while full 2 1/4 x 2 1/4 is 56.25mm square, I believe transparencies from my Hasselblad are 54 x 54 mm; so in our case 645 would be 54 x 40.5 mm. Right?]
Al Bowers
 
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