At 17:01 5/8/01, Frieder Faig wrote:
While working with my spreadsheed, it occours more questions than answers.
The real focus lenght might differ about +/- 5%.
And a lens isn`t a ideal thin lens. When you calculate macro-distances this
diffrences values matters.
As theoretical ideal 135mm my spreadsheed gives the following values :
Auto-Macro-Tubus max. extension (58mm):
Distance to film: 64.2 cm
working distance: 42.4 cm
lenght of equipment 22.0 cm
Now I´ve made some measurements:
For the 135mm /F 4.5 Macro I've meassued the following:
Auto-Macro-Tubus max. extension (58mm):
Distance to film: 61.0 cm
working distance: 39.2cm
lenght of equipment 22.0 cm
with additional extension tubes 7,14,and 25 (105mm):
Distance to film: 53.6 cm
working distance: 27.0cm
lenght of equipment 26.7 cm
Though the 135mm isn`t a thin lens, this values are hard to guess.
The best guess is 126mm real focal lenght and 26mm distance between
priciple planes
(dt. Hauptebenenabstand?).
Does somebody know the real values?
I started a spreadsheet last night. Pulled data from the eSIF files
realizing all of these (including focal length) are approximate
values: minimum field width (at closest focus; probably rounded to nearest
centimeter) and minimum focus distance (probably rounded to nearest
decimeter). Still working it and plan to employ "fuzzy logic" to reconcile
differences using one or two of them to calculate other values that can
derived several different ways using the data from the eSIF. It's one of
the reasons any results would be approximate; the eSIF data for each lens
is approximate and not consistent enough as a set for highly accurate results.
-- John
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