Question about sal50f/1.4 vs sal16-50f/2.8

Started May 2, 2012 | Discussions thread
New MemberPosts: 10Gear list
Re: Effective focal lengths vary with distance
In reply to crisno1, May 4, 2012

You make some very good points but it is important to remember that the difference between f2.8 and f1.4 is two stops not six. It may be six clicks on your aperture scale, but each click is not a full stop. A full stop makes a doubling or halving of the light that is let into the sensor, so it is important to know the difference between a click and stop.

If you start at f2.8, the next larger f stop is f2, and then you get to f1.4.

There is a very easy way to remember the whole f stop scale, it only requires you to remember five things;

1. The Scale starts at f1
2. The next whole stop is at f1.4
3. The next whole stop is double the first stop (f1) or f2
4. The next whole stop is double the second whole stop (f1.4) or f2.8

5. Repeat the pattern of #3 and #4, by doubling first the multiple of f1, then double the multiple of f1.4

Here is the whole FULL Stop scale (notice the pattern).

f4 (double f2)
f5.6 (double f2.8)
f8 (double f4)
f11 (double 5.6)
f16 (double f8)
f22 (double f11)
f32 (double f16)
f44 (double f22)
f64 (double f32)

All other stops are half or one third stops.

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