hyperfocal distance for g2

[dfleming]

A shortcut for calculating hyperfocal distance for 35mm format (explained in the popphoto.com forums a few days ago) got me thinking about developing a shortcut for the G2.

The approximate hyperfocal distance (in feet) for the Canon G2 lens, set to f/5.6:

H = (f*f)/10

or, the focal length squared divided by 10.


(Note that this shortcut will work for any digital camera for which the circle of confusion is 0.006 mm, which includes the A40, S30, S40, G1, Pro 90 IS).

Because the focal lengths for the G2 zoom lens are short, the math is easy to do:

7mm lens: H = 7*7/10 = 4.9 feet
8mm lens: H = 8*8/10 = 6.4 feet
10mm lens: H = 10*10/10 = 10 feet
20mm lens: H = 20*20/10 = 40 feet


These numbers are close enough for any work in the field. The actual numbers for f/5.6, calculated using the DOFMaster calculators ( http://www.dofmaster.com ), are:

7mm lens: H = 4.8 feet
8mm lens: H = 6.2 feet
10mm lens: H = 9.7 feet
20mm lens: H = 39 feet


I've also updated an article ( http://www.dofmaster.com/hyperfocal.html ) that gives practical advice about using hyperfocal distance in the field.


Derivation:

The shortcut is based on using 0.006mm for the circle of confusion. The derivation of the shortcut from the hyperfocal distance equation follows:

H = (f*f)/(N*c*304.8)

where

H = hyperfocal distance in feet
N = f-number
c = circle of confusion
and 304.8 is the conversion from millimeters to feet

When N=5.6 and c=0.006, the denominator is:

5.6*0.006*304.8 = 10.24


And without causing any significant error, we can just say the denominator equals 10.

Thus, the hyperfocal distance equation becomes:

H = (f*f)/10


Don

[Leighow]

DON

I will keep it short.

I had not appreciated this relationship even though in 1958 I took a half-semester course in thick and thin optics. Very thorough. Very professional. Very useful.

Your approach (given a specific setting) can help "gut feel" photographers such as myself to take more effective photographs. Excellent. I will study and apply.

Thank you very much.


HOWIE

[G2Brooklyn]

This link is dead. http://www.dofmaster.com/hyperfocal.html Could you please bring it back to life. I need the information that it holds.

The Sponge

[dfleming]

The site was down for a period of time yesterday. It's back up today, so the link should work.

Don