Archived posting to the Leica Users Group, 2003/04/24
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At 7:22 PM +0800 4/24/03, Red Dawn wrote:
>----- Original Message -----
>From: "Jim Laurel" <jplaurel@nwlink.com>
>Subject: [Leica] Digital Aesthetic
>
>
>
>> Correct me if I'm wrong, but I believe depth of field is related to focal
>> length and aperture size alone. The depth of field of a 25mm lens is the
>> same regardless of the size of the film or digital sensor. Consider the
>> example above and let's assume that the film shooter is using a 50mm set
>to
>> f1.4. To acheive the same FOV, the DSLR user will need a 31mm lens. But
>> lenses around this focal length with maximum apertures of f1.4 are few and
>> far between, not to mention that a 31mm lens at f1.4 will still have more
>> DOF than a 50mm at 1.4. The DSLR shooter could use the same 50mm f1.4
>lens,
>> and back off from the subject, but then again, the increased distance to
>> subject will result in increased DOF.
>
>Hi Jim,
>
>i do believe u're wrong.
>
>Let's take the EOS 10D with a 50mm f1.4 lens (a combo which i happen to own
>as well) and shoot a subject at f1.4. The equivalent focal length is 50 x
>1.6 = 80mm.
>
>Now let's then take a 80mm R Summilux and mount it on a EOS 1v film body
>(again i also own this body), frame the SAME subject and keep the
>composition and subject size EXACTLY THE SAME.
>
>The 2 pictures will look identical because we have kept the subject size /
>magnification and framing the SAME. If u compare the 2 shots, they will have
>the SAME DOF. This is because the subject distance is constant, and so is
>the aperture.
>
>Remember, DOF is also affected by subject distance! Don't take my word for
>it though - do your own visual tests and find out for yourself :)
>
>The only thing u're right is the difficult of finding lenses to simulate
>your favourite focal lengths. U're right in the sense if u want a TRUE 50mm
>on a DSLR, and nothing but a 50mm, it is impossible to find a 31mm lens that
>will fit the bill. However, you can use a 35mm lens on the 10D to simulate
>56mm.
>
>Can you really tell the difference between 56mm and 50mm in actual real life
>shooting? I don't think so :)
>
>Boon Hwee
Jim got it right. DOF is dependent on focal length and aperture value
alone, and only slightly modified by the different circle of
confusion criteria for different formats.
The shot with the 10D/50 will have significantly more DOF than the
one with the 80mm on 24x36.
Anyone who has shot different formats will attest to this. A 180mm
lens has the same angle of view on 4x5 as a 50 has on 24x36. Shoot
both of a subject at the same distance and aperture, say f/8, and
you'll instantly see that the 24x36mm shot has immensely greater
depth of field.
Optical theory substantiates this.
- --
* Henning J. Wulff
/|\ Wulff Photography & Design
/###\ mailto:henningw@archiphoto.com
|[ ]| http://www.archiphoto.com
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