[pure-silver] Re: Depth of Field (35mm vs. 4x5 or 8x10)
- From: "Richard Knoppow" <dickburk@xxxxxxxxxxxxx>
- To: <pure-silver@xxxxxxxxxxxxx>
- Date: Sat, 30 Oct 2004 13:32:47 -0700
----- Original Message -----
From: "Jim Brick" <jim@xxxxxxxxx>
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Friday, October 29, 2004 5:48 PM
Subject: [pure-silver] Re: Depth of Field (35mm vs. 4x5 or
8x10)
> At 04:36 PM 10/29/2004, Gene Johnson wrote:
>
>
>>1600mm? You sure about that Jim? I was thinking more
>>like 400. He used a
>>100mm on his 35mm camera
>
>
> The 4x5 frame is roughly 16x the 35mm frame. This is all
> about image
> magnification. 16x 100 = 1600.
>
> But I could be wrong and would gladly accept another
> proof.
>
> Jim
>
>
The diagonal of a 35mm frame and thus the equivalent
focal length depends on whether the frame is cropped or not.
Assuming it is cropped to the same aspect ratio as a 4x5
negative (1.25:1) the effective dimentions are 24 x 30 mm.
The diagonal is about 38.5mm, this is then the "normal"
focal length.
The diagonal of the actual picture area of a 4x5 film is
150mm, so the angle of view for the 35mm camera with the
38.5 mm lens will be the same as a 4x5 with a 150mm lens.
The ratio of the diagonals is about 3.9. This is the factor
to multiply a 35mm lens by to get the equivalent 4x5 focal
length or to devide the 4x5 lens by to get the equivalent
35mm FL.
The diagonal of a full 35mm frame is around 45mm, the
common 50mm lenses are slightly long focus. Since 35mm
frames are very often cropped to 4x5 (1.25:1) dimentions I
think the popularity of 35mm FL lenses for 35mm cameras is
explained.
---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx
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