How much "brighter" is 50 1.2 vs 1.4 & 1.8?

[KENTGA]

Frequently there are questions aobut the 50mm 1.2L, 1.4 and 1.8 lenses. How much of an f/stop gain do you get between 1.4 and 1.8 and 1.2 and 1.4 or 1.8? Irealize many buy to 1.2 for shallow DOF (and they just want Canon's "best" lens), but it's hard for me to think you gain that much of a gain in f/stops.

Just wondering--- not trying to make a buying decision.

Kent

 

[Lemming51]

f/1.8 is 2/3 stops slower than f/1.4
f/1.4 is 1/3 stop (or 1/2) slower than f/1.2

If the metering with f/1.8 give a shutter speed of 1/30, then
f/1.4 ==> 1/50
f/1.2 ==> 1/60 or 1/70

Frequently there are questions aobut the 50mm 1.2L, 1.4 and 1.8
lenses. How much of an f/stop gain do you get between 1.4 and 1.8 and
1.2 and 1.4 or 1.8? Irealize many buy to 1.2 for shallow DOF (and
they just want Canon's "best" lens), but it's hard for me to think
you gain that much of a gain in f/stops.

Just wondering--- not trying to make a buying decision.

Kent

 

[Victor Engel]

Given two f-stops, A and B, to determined the number of stops difference, first compute the quotient:

C = A/B

The number of stops difference is then log(C) / log(sqrt(2))

Let's try this with f/1.8 and f/1.2 for example.

C = 1.8/1.2, so the number of stops difference is log(1.8/1.2) / log(sqrt(2)) = 1.2 stops.

The difference between f/1.8 and f/1.4 is 0.73 stops
The difference between f/1.4 and f/1.2 is 0.44 stops

So why doesn't 1.2 stops from my first example equal the sum of the other two examples?

1.2 = 0.73+0.44

Actually, it does when you use the same number of significant digits. The f-stops on the lens are given in two digits, so our answer needs to also be in two digits.

The apertures are not exactly as marked. These calculations could vary probably by up to about 1/3 stop due to rounding.
--
http://www.pbase.com/victorengel/

 

[KENTGA]

Thanks Lemming and Victor. Frankly, I didn't realize that there were 1.2 f/stops between 1.2 and 1.8. Maybe that's why people fork-out that msny $$$ for the 1.2 (and the bokeh).

Kent

 

[Victor Engel]

Thanks Lemming and Victor. Frankly, I didn't realize that there were
1.2 f/stops between 1.2 and 1.8. Maybe that's why people fork-out
that msny $$$ for the 1.2 (and the bokeh).

Aperture value is probably more intuitive for estimating how many stops between values since it's a linear scale (see http://en.wikipedia.org/wiki/F-stop ). By the way, you may notice on the chart on that page that f/1.2 and f/1.8 are only one stop apart. These sorts of differences are common and are because of rounding.

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http://www.pbase.com/victorengel/

 

[BAK]

Full stops worked out to f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, f32, f45 and here wer were just about pout of lenses,

So, f1.2 is just a bit smaller than f1, and f1.8 is just a bit bigger than f2, and there you go. A bit over a stop's worth of difference.

Everything gets multiplied by 1.4 because area of a circle is involved.

Common belief holds that a lens is sharper once it is stopped down a bit, so for a thousand dollars, you can buy a 1.2 lens to give you the same sharpness as a 1.8 lens if the 1.8 lens was really sharp wide open, instead of needing to be stopped to f2.

 

[Victor Engel]

So, f1.2 is just a bit smaller than f1,

That is more than half a stop, not just a bit. The 0.2 difference from 1 1.2 is much more significant than the difference from 1.8 to 2. You can't look at the differences. You need to look at the quotients:

1.2/1 = 1.2 (1 1/5)
2/1.8 = 1.1 (1 1/9)

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http://www.pbase.com/victorengel/

 

[Chez Wimpy]

Thanks Lemming and Victor. Frankly, I didn't realize that there were
1.2 f/stops between 1.2 and 1.8.

There aren't.. its creative rounding on Canon's part. The 1.2 is a full stop faster than the f1.8, and 2/3rds of a stop slower than the old f1.0. If you do test exposures looking at the histogram you can see for yourself. Both of Canon's f1.2 lenses are f1.2 in the "1/3 a stop faster than f1.4" sense.

FWIW, the 1/3 series on EF cameras (reads out as) 1.0,1.1,1.2,1.4,1.6,1.8,2.0 ect

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-CW

 

[gdanmitchell]

The difference is quite tiny, and it is hard to imagine that spending the price of the f/1.2 lens for that reason would ever make sense.

You can demonstrate the magnitude of the difference by using smaller stops and your depth of field preview button. A rough comparison would be to compare f/4 and something in the neighborhood of f/3.

Dan

Frequently there are questions aobut the 50mm 1.2L, 1.4 and 1.8
lenses. How much of an f/stop gain do you get between 1.4 and 1.8 and
1.2 and 1.4 or 1.8? Irealize many buy to 1.2 for shallow DOF (and
they just want Canon's "best" lens), but it's hard for me to think
you gain that much of a gain in f/stops.

Just wondering--- not trying to make a buying decision.

Kent

--
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G Dan Mitchell - SF Bay Area, California, USA
Blog & Gallery: http://www.gdanmitchell.com/

 

[Roentarre30]

Frequently there are questions aobut the 50mm 1.2L, 1.4 and 1.8
lenses. How much of an f/stop gain do you get between 1.4 and 1.8 and
1.2 and 1.4 or 1.8? Irealize many buy to 1.2 for shallow DOF (and
they just want Canon's "best" lens), but it's hard for me to think
you gain that much of a gain in f/stops.

Just wondering--- not trying to make a buying decision.

Kent

50L provides better accuracy in AF (even with focus shift), better overall image rendering and better spatacular highlight performance

http://www.roentarre.com/Gallery.aspx?id=1&lid=3

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Roentarre, Melbourne, Australia
http://www.roentarre.com
http://www.themesoftime.com
http://www.themesoftime.com/Gallery.aspx