# Field of view - need help with the math

Discussion in 'Digital Photography' started by Peabody, Nov 13, 2011.

1. ### PeabodyGuest

I have an old Kodak Medalist film camera that I want to shoot a few
rolls with. It has a 100mm lens, and uses 120 film (actually 620)
and gets 8 exposures per roll. So I think that's what's called the
6x9 frame size, which is actually 56 x 84mm.

I want to know what lens focal length on my Canon crop sensor
camera would give the same field of view as the Kodak. That's a
14.8 x 22.2mm sensor.

Is it 26.4mm? Based on just eyeballing the viewfinders, using the
kit lens on the Canon, that appears to be about right.

Peabody, Nov 13, 2011

2. ### BruceGuest

Peabody <> wrote:

>I have an old Kodak Medalist film camera that I want to shoot a few
>rolls with. It has a 100mm lens, and uses 120 film (actually 620)
>and gets 8 exposures per roll. So I think that's what's called the
>6x9 frame size, which is actually 56 x 84mm.
>
>I want to know what lens focal length on my Canon crop sensor
>camera would give the same field of view as the Kodak. That's a
>14.8 x 22.2mm sensor.
>
>Is it 26.4mm? Based on just eyeballing the viewfinders, using the
>kit lens on the Canon, that appears to be about right.

The diagonal of a 56 x 84mm "sensor" is 100mm. The lens on your
Medalist therefore has a focal length equal to the diagonal.

The diagonal of a 14.8 x 22.2mm sensor is 26.7mm. So to get the same
angle of view as the Medalist, you would need to choose a focal length
that is equal to the diagonal. So the answer is 26.7mm.

Bruce, Nov 13, 2011

3. ### dj_nmeGuest

On 13/11/2011 3:27 PM, Peabody wrote:
> I have an old Kodak Medalist film camera that I want to shoot a few
> rolls with. It has a 100mm lens, and uses 120 film (actually 620)
> and gets 8 exposures per roll. So I think that's what's called the
> 6x9 frame size, which is actually 56 x 84mm.
>
> I want to know what lens focal length on my Canon crop sensor
> camera would give the same field of view as the Kodak. That's a
> 14.8 x 22.2mm sensor.
>
> Is it 26.4mm? Based on just eyeballing the viewfinders, using the
> kit lens on the Canon, that appears to be about right.
>

100mm lens on a 6x9 camera is a "normal" lens (roughly equal to the
diagonal of the film frame), just like a 50mm lens is on a 35mm camera.
Doing the math with a crop factor of 1.6 for the Canon camera, 31.25mm
would be exactly spot-on.
Any focal length from 28mm to 35mm would be close enough, really.

If you want to be ultra finicky about the correct length of a normal
lens for 35mm, then you'd use 43.5mm on a 24x36mm camera and 27.2mm on
1.6 crop factor camera.

dj_nme, Nov 13, 2011
4. ### Kennedy McEwenGuest

In article <>, Bruce
<> writes
>Peabody <> wrote:
>
>>I have an old Kodak Medalist film camera that I want to shoot a few
>>rolls with. It has a 100mm lens, and uses 120 film (actually 620)
>>and gets 8 exposures per roll. So I think that's what's called the
>>6x9 frame size, which is actually 56 x 84mm.
>>
>>I want to know what lens focal length on my Canon crop sensor
>>camera would give the same field of view as the Kodak. That's a
>>14.8 x 22.2mm sensor.
>>
>>Is it 26.4mm? Based on just eyeballing the viewfinders, using the
>>kit lens on the Canon, that appears to be about right.

>
>
>The diagonal of a 56 x 84mm "sensor" is 100mm.

Not quite.

>The lens on your
>Medalist therefore has a focal length equal to the diagonal.
>
>The diagonal of a 14.8 x 22.2mm sensor is 26.7mm.

Not quite.

>So to get the same
>angle of view as the Medalist, you would need to choose a focal length
>that is equal to the diagonal. So the answer is 26.7mm.
>

If you are going to dispute Peabody's figure by little over 1% then you
need to ensure that your own figures, and intermediate terms, are at
least that precise - your first certainly isn't. Because of that, your
answer is about 1% too high. So Peabody's own figure of 26.4mm is more
accurate.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's pissed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)

Kennedy McEwen, Nov 16, 2011