Pages

Saturday, 7 February 2015

Increasing depth of field (DOF)

Hyperfocal distance is not something that trips off the tongue in this modern age of auto focus. In fact digital camera lenses do not have the facility to take advantage of this compositional tool. You just have to compare today’s lens with yesterdays they don't have aperture settings and therefore you can not play with hyperfocal distance settings.


So what is Hyperfocal distance?

When a lens is set to infinity, the depth of field (D.O.F) closest to the camera is known as the Hyperfocal distance for that aperture. If you have an older lens its barrel will be marked with these distances.





How to change the Hyperfocal distance.


Set the lens focus to infinity, and then read the lower mark for whatever aperture you have set. If you then refocus the lens to the lower mark known as the optimum distance you will increase your depth of field by fifty per cent of the optimum.


For example:


This was made using a
 telephoto lens at close distance.
 The use of hyperfocal distance has
 pulled the area of sharp focus
to the front of the ball.
I have used an old 50mm Nikon lens (pictured) to show how it works. I have set the focus to infinity and the aperture to F16. The good thing about this lens is that it shows the upper and lower limits of each aperture with lines on the lens barrel. Looking to the right (marked A) you can see that the last line on the lens barrel is opposite the five meter mark (about fifteen feet). By resetting the focus to optimum in this case five (A). Then look at the lower limit (marked B) for F16, it is about two and a half meters (eight and half feet). The resetting will extend the overall sharpness of the picture by an extra two and a half meters which is 50 percent of the optimum.

The longer the lens the greater the increase is. For argument, an 80 mm lens with an aperture of F22 set, would have a depth of field from 2.8 meters all the way to infinity when optimum focus is used. Instead of 5.6 meters to infinity.


If  hyperfocal distance had been
used with this picture the
 front post would be sharp.
 
In some cases where you do not have aperture lines on the barrel of the lens some cameras and lenses have a shut down button. This allows you to see before you press the shutter where the hyperfocal distance ends. So you can adjust it if needs be.

Being able to increase the depth of field (D.O.F) can be very useful when using medium and long telephoto lenses for subjects close to the lens, allowing narrow fields of sharpness to be moved. This makes sure the front of the item is in focus.