Hallo,
I´ve made some toughts about the speed difference from Lenses, I want to share.
Purpose: Question was: Difference 50 mm F /1.2 to F1.4 or F/1.8
Now I calculated the difference in of F-stops with:
LV (F) = Log( F^2) /Log (2)
(LV is not really light value, but the difference in light values when shutter
speed remains)
With this Formula it is possible to calculate a decimal equivalent for uneven
f-stops.
Now the official f-stop series is:
1 0.00
1.2 0.53
1.4 0.97
1.414 1.00 !
1.8 1.70
2 2.00
2.8 2.97
3.5 3.61
4 4.00
4.5 4.34
5 4.64
5.6 4.97
6.3 5.31
6.8 5.53
8 6.00
This would indicate that F1.2 is about a half F-stop faster than F1.4, which is
0.7 F-stops faster than F1.8.
Now it is very unlikly that the Zuiko lenses exact match this academic values.
But I found the meassured values from moder photography which are
in the web at:
http://brashear.phys.appstate.edu/lhawkins/photo/mp-zuiko-tests.txt
Thanks to R.Lee Hawkins.
lens actual
speed LV:
REF 1 0.00
1.2/50 1.26 0.67
1.4/50 SC 1.37 0.91
1.4/40MC 1.44 1.05
1.8/50 1.86 1.79
The SC and MC-Version of Zuiko 50mm F/1.4 do slightly differ in Speed.
0.16 matches 1/6 EV which is half the difference which is relevant.
All tested F1.8 lenses are about the same value.
So this would mean:
The Zuiko 50mm/F1.2 is ~1/4 -F-stop faster than the SC-50 F/1.4
The Zuiko 50mm/F1.2 is ~0.4 -F-stop faster than the MC-50 F/1.4
The Zuiko 50mm/F1.2 is ~1.1 -F-stop faster than the 50 F/1.8
Now I meassured with my OM2sp the same wall with the 1.4/50 SC and
the 1.8/50 MC. The difference is about 1/3~1/2 F-stop only. Hmmm.
Seems the lever from one lens isn`t too accurate, or the vingetting problem??
Now l`m curious about to see the test slides!
Frieder Faig
PS: The values of other MP-tested Zuiko`s:
lens actual
speed LV:
1.2/50 1.26 0.67
1.4/50 SC 1.37 0.91
1.4/40MC 1.44 1.05
1.8/50 1.86 1.79
2.0/21 1.91 1.87
2.0/35 2 2.00
2.0/180 2.01 2.01
2.0/40 2.03 2.04
2.0/90M 2.04 2.06
2.0/100 2.05 2.07
3.5/21 2.58 2.73
2.8/135 2.79 2.96
2.8/35 2.81 2.98
2.8/100 2.81 2.98
2.8/180 2.9 3.07
2.8/24 2.93 3.10
3.5/28 3.5 3.61
3.5/18 3.51 3.62
3.5/50M 3.64 3.73
4/200 4.01 4.01
8/500 8.27 6.10
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