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Aperture step question
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PostPosted: Thu Aug 06, 2015 8:49 pm    Post subject: Aperture step question Reply with quote
Hello I bought a 55mm f1.7 lens that has a aperture steep between f1.7 and 2.8 that is exactly one steep down from f1.7 and I wonder what the aperture is there .


PostPosted: Thu Aug 06, 2015 9:02 pm    Post subject: Reply with quote
it will be f2. The f1.7 max aperture is exactly half a stop between f1.4 and f2


PostPosted: Thu Aug 06, 2015 9:10 pm    Post subject: Reply with quote
But the steep is one step down from f1.7(half the sutter speed)from 1,7 to 2 is half a stop as you say,


PostPosted: Fri Aug 07, 2015 9:38 am    Post subject: Reply with quote
One step down=fx1.4
One step up=fx0.7


PostPosted: Fri Aug 07, 2015 2:19 pm    Post subject: Reply with quote
Zeeke wrote:
Hello I bought a 55mm f1.7 lens that has a aperture steep between f1.7 and 2.8 that is exactly one steep down from f1.7 and I wonder what the aperture is there .

1 stop less light than f1.7 would be f2.4
f1.7 to f2.8 is 1.5 stops or 3, 1/2 stops (f1.7 (1/2) f2 (1/2) f2.4 (1/2) f2.8 ) shutter speed: 1/1000 @ f1.7, 1/500 @ f2.4, 1/333 @ f2.8
Half way would be f2.2

A nice table here:
http://www.distantfuturejosh.com/posts/tag/f-number/


More here:
https://en.wikipedia.org/wiki/F-number
Quote:
To calculate the steps in a full stop (1 EV) one could use

2^(0×0.5), 2^(1×0.5), 2^(2×0.5), 2^(3×0.5), 2^(4×0.5) etc.

The steps in a half stop (1/2 EV) series would be

2^(0/2×0.5), 2^(1/2×0.5), 2^(2/2×0.5), 2^(3/2×0.5), 2^(4/2×0.5) etc.

The steps in a third stop (1/3 EV) series would be

2^(0/3×0.5), 2^(1/3×0.5), 2^(2/3×0.5), 2^(3/3×0.5), 2^(4/3×0.5) etc.


PostPosted: Fri Aug 07, 2015 5:29 pm    Post subject: Reply with quote
Thanks for your replies
Regards Sverker
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