(12C) Hyperfocal Distance

[Dieter]

(04-30-2018 07:42 PM)Mike (Stgt) Wrote:  I only wanted to know how you justify to "ignore" a difference of up to 5% and more on the one hand and otherwise mind about the exact location of the reference point. In addition with the repeated "etc. etc. etc." you signify there are even more possibilities or questions and you know about it.

There is a simple answer: just because I know of the inherent inaccuracy of the input data and the result I do not care about a difference of one focal length and consider the simplified formula more than good enough.

In detail: Why care about 5 cm difference in the hyperfocal distance when 1% tolerance in the focal length causes twice that difference? And how would one distinguish 10 m and 10,05 m on the distance scale even of a classic 1970s manual focus rangefinder lens? Let alone today's virtually useless scales on AF-lenses where the 1-m-mark is right beside the infinity symbol. #-}

Re. "where to align the tape measure": the formula (with the added f) calculates the distance measured from the lens' front principal plane. So let's hope you got the manufacturer's data sheet for the lens in question. On the other hand the distances scales on lenses refer to the image plane. Which is roughly (!) one more focal length away. But then... who cares – see above.

Addendum:

If I got the math right, the hyperfocal distance from the image plane is f²/Ac + 2f + Ac. Here the term Ac can be neglected as it is within ≈ 1 mm for film / sensor formats up to "full frame". Even in large format photography it's merely 2 cm (f/90 · 0,2 mm) which is the same order as the principal plane distance which still would have to be added or subtracted, depending on the lens construction. Anyway, here is a 12C version that implements the complete formula:

Edit: new version with the formula rearranged as (f + Ac)² / Ac

Code:

01  1/x
02  ,
03  0
04  3
05  x
06  x
07  +
08  ENTER
09  ENTER
10  LstX
11  /
12  x
13  EEX
14  3
15  /
16  GTO 00

This yields the hyperfocal distance measured from the image plane. Which is usually marked on the camera body, so you get an unambiguous reference point. ;-)

As before, the input is  f [ENTER] A [ENTER] crop factor.
35 [ENTER] 11 [ENTER] 1 [R/S] => 3,78

If you want a slightly shorter version simply take the previous one and add another "+" before the "EEX 3". This ignores the Ac term.

Dieter