Luminous Landscape Forum
Equipment & Techniques => Medium Format / Film / Digital Backs – and Large Sensor Photography => Topic started by: Alex MacPherson on November 06, 2010, 03:41:06 am
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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?
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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 |
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For simplicity sake (assuming 1:1) I've always used focal length x .67 to approximate the 135mm equivalence.
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In case you want to skip the math...
http://www.captureintegration.com/2009/02/03/focal-length-equivalent-calculator/
Tell it what you know (e.g. "I know what an 85mm looks like on a 5DII") or and it will tell you what you should use with a given digital back.
Doug Peterson (e-mail Me) (doug@captureintegration.com)
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In case you want to skip the math...
Doesn't everyone write formulae for fun?
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Thanks Doug!
So just to make sure that I am reading the calculator correctly:
If I have an 80mm lens on a Hasselblad V with a P30 back... the 35mm equivalent is 115mm ?
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P30 sensor = 44 x 33 mm
35mm = 36 x 24mm
80mm lens on Hassy V (P30) --->
Width: 80mm x 36/44 = 65mm
Height: 80mm x 24/33 = 60mm
Regards
Anders
P.S. If want diagonal, first calculate diagonal of frame for each format ( sqrt( w*w + h*h ), then do same as above.
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Thanks Doug!
So just to make sure that I am reading the calculator correctly:
If I have an 80mm lens on a Hasselblad V with a P30 back... the 35mm equivalent is 115mm ?
I think you are misreading the calculator.
See the attachment which should clarify.
You are using a P30 with an 80mm, so you should enter "80mm" into the column of the P30. Then look in the 35mm dSLR column and see that the equivalent is 63mm.
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You are using a P30 with an 80mm, so you should enter "80mm" into the column of the P30. Then look in the 35mm dSLR column and see that the equivalent is 63mm.
80/90mm is normal for 66, (Hassy V), and 43/50 is normal for 35, but you are comparing a square to a rectangle, and that is when it helps to consider the long and the short of the rectangle, and not just the diagonal.
...and you get 44mm for 35mm equivalent of an 80mm on a Hassy V, but if you are using a P30 on a Hassy V body, it is the P30 number which you want.
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Fast and rough rule-of-thumb I used when I compared 6x6 from my 'blad to 35mm full-frame was that the 35mm lens was roughly 5/8ths the equivalent focal length--multiply the H'blad's focal length by 0.675 to get an approximation.
Of course, I comparing film to film. Using a digital back changes the factors due to the smaller-than-film digital backs for the classic 6x6 system...
For 35mm to 6x6, you need to multiply the FL by 8/5ths, or 1.6 to get the equivalent length. Thus, 50mm on full-frame is about 80mm on the H'blad. This gets you quickly to the ball park.
Of course, your results will vary.
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Fast and rough rule-of-thumb I used when I compared 6x6 from my 'blad to 35mm full-frame was that the 35mm lens was roughly 5/8ths the equivalent focal length--multiply the H'blad's focal length by 0.675 to get an approximation.
Of course, I comparing film to film. Using a digital back changes the factors due to the smaller-than-film digital backs for the classic 6x6 system...
For 35mm to 6x6, you need to multiply the FL by 8/5ths, or 1.6 to get the equivalent length. Thus, 50mm on full-frame is about 80mm on the H'blad. This gets you quickly to the ball park.
Of course, your results will vary.
A very useful conversion factor for miles and kilometres too, that 8 to 5!
Rob C
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In the real world, I wave two fingers or a fist at the subject, and this tells me which lens has the right field (angle) of view.
Field of view is format at focal length... I usually scale it up to arm's length... for 300mm on 53mm one arm's length is two focal lengths, one fist is two formats... simple?
One finger at arm's length is about one and a half degrees.
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Doesn't everyone write formulae for fun?
I do! :)
Dick, I believe it was Meatloaf who sang, "You took the cell references right out of my mouth, ..."
Ray