DOF issues ,and hyperfocal distance

[cp_wong]

Dear all,

as a green LF user, i read the Lesile Stroebel's book " view camera

technique", as i want to solve the DOF issues.

there was a formula used to calculate the hyperfocal distance,

nearest distance in focus , farthest distance in focus , and DOF.

---hyperfocal distance (H)= fxf / ( f-N x COF) , f : focal length of

lens , f-N : stop no. , COF : circle of confusion.i used 6x9cm

format , with 90mm lens, take COF as 1/500 inch.

--- nearest distance in focus = HxU/(H+U), H : hyperfocal distance,

U : object distance for lens focussing

--- farthest distance = HxU /( H-U)

--- DOF = farthest distance in focus -nearest distance in focus

Question :

1/ if we focus at a distance nearer than the hyperfocal distance ,

the effect will be nearest distance in focus decreased , but also the

farthest distance ,too and can't get the "infinity" in focus.

2/ But what about if we focus at a distance farther than the

hyperfocal distance? from the formula, theoretically , the farthestv

distance will be negative !!!!!

but will happen practically , and why?

many thanks.

[pat_krentz]

What distance are you trying to focus at? Pat

[cp_wong]

from the formula above , U represent the distance i will focus,,so if U > H , then H-U will be negative!!!

[carl_weese]

All depth of field formulas are based on arbitrary definitions of what will be considered "sharp enough." This means that if you set the focus to a distance beyond the hyperfocal, you will lose some sharpness in the foreground, but will gain sharpness in the distance, compared to the exact hyperfocal setting for the lens length and aperture. The focus doesn't "go past infinity" but simply improves at infinity. ---Carl