F/3 Rule of Thumb for Landscape Photography

For 35mm landscape photography, where distant objects such as moutains, buildings are the main object of interest in composition, focus the lens at infinty is the way to go. That greatly simplies depth of field in travel photography.

But how to choose aperture in the middle of busy travel schedules ? You are not going to pull out a Depth of field chart are you ?

I need a very very simple "rule of thumb"

By analysis of the travel photo habit of myself and other poeple, I find that most of the time, people take pictures hand held camera at eye level.

A Minox 35mm (or a SLR )held at eye level is ahout 1.5-1.6 meter off ground, holding the camera level, the closeset point visible in the viewfinder is the point of ground cut off by the bottom line of of viewfinder.

Now suppose I want that point to be the hyperfocal point , so what is the fstop ?

I invented "Martin Tai's F/3 rule of thumb for landscape", as I found out, that the required aperture = one third of focal length of 35mm camera !

Once I set the camera's aperture at F/3, focus the lens at infinity, then depth of field rules tells us that everything from hyperfocal point to infinity will be sharp---- that is, everything I see in the viewfiner will be sharp !

For Minox GT-E, I set it at 35/3 = f11 , focus at infinity and shoot.

For my Leica Vario-Elmar 28-70 zoom lens which has no DOF scale as most zoom lenses are, I too set fstop = one third of focal length, and focus at infinity. for example if I use 28mm short end, I choose 28/3 = F9 if I select F=45mm I select aperture at 45/3= F16.....

-- Anonymous, February 15, 2000

Answers

Proof of F/3 Rule

The mathematic proof of "Martin Tai one third focal length rule of thumb" was posted to usenet .

      
                                                                 
mountain
                             
                                                      ---
                                              ---
                                      ----
                                 ---
                           
---                                                                   
                            
                    -----        
            -----
   () ---                                 ()
    |  -                                   |
    |     ---                             /| \
  h |           ----                       |
    |                ----                 | \
   / 
\---------------------------------------------------------------------
                      -
                         D                                 infinity

When a 35mm camera is held vertical and point at distant horizon, the closest point on the ground cut of by the bottom line of viewfiner is

            D=F*h/18  
   

in which

• F is focal length of lens,
• h is height of camera off ground,
• and 18 is half of 36mm frame length.

Let D= hyperfocal distance H=F*F/(fstop*coc)

where

• F= focal length,
• coc= circle of confusion.

Hence

       F*h/18 = F*F/(fstop*coc );

from which

          fstop = 18*F/(h*coc )

Select

• h =1.6 meter,
• coc =1/30 mm

then

         fstop =~  F/3. 

Q.E.D.

Lu Yu Pick Tea in the Mountains

-- Anonymous, February 15, 2000