[pure-silver] Re: Depth of Field (35mm vs. 4x5 or 8x10)

----- 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 

=============================================================================================================
To unsubscribe from this list, go to www.freelists.org and logon to your 
account (the same e-mail address and password you set-up when you subscribed,) 
and unsubscribe from there.

Other related posts: