Aperture f-stop multiplier?

[Nigels]

Not really sure where to ask this question. And it may be a silly question but here goes; If the multiplier for one stop of aperture is 1.414 (the square root of 2) then what is the multiplier for a third of a stop?

[Greg Lockrey]

1.1545561

[Struan Gray]

1.12246 or so.

You want a number that when multiplied by itself three times gives the correct multiple for a stop's worth of exposure change. Thus you take the cube root of 1.414, which is the sixth root of two.

[Joanna Carter]

.4714045

Hmmm, anything less than 1 is going to reduce the result, not increase it

[Greg Lockrey]

Hmmm, anything less than 1 is going to reduce the result, not increase it

yeah, I retunck it....see above. Take sqrt of 1.3333.

[jb7]

ask me one on sport...

[Greg Lockrey]

1.12246 or so.

You want a number that when multiplied by itself three times gives the correct multiple for a stop's worth of exposure change. Thus you take the cube root of 1.414, which is the sixth root of two.

That's some heavy siffering. Aren't we dealing with an area of a circle and how it multiplies itself by 2 from one diameter to the next? You're going to have to explain cube's and sixth roots to me when you are just dealing with square areas.

[Bill Kumpf]

It is my understanding the multiplier is the “square root of one plus the fraction”

If you want ½ stop increase, the multiplier is the square root of (1+ ½).

Exposure Increase
f/stop Time multiplier Aperture Increase

1/12 1.059 1.040833
1/6 1.122 1.080123
1/4 1.189 1.118034
1/3 1.260 1.154701
1/2 1.414 1.224745
1 2.000 1.414214


Of course it has been a loooong time since I studied math.

[Greg Lockrey]

It is my understanding the multiplier is the “square root of one plus the fraction”

If you want ½ stop increase, the multiplier is the square root of (1+ ½).

Exposure Increase
f/stop Time multiplier Aperture Increase

1/12 1.059 1.040833
1/6 1.122 1.080123
1/4 1.189 1.118034
1/3 1.260 1.154701
1/2 1.414 1.224745
1 2.000 1.414214


Of course it has been a loooong time since I studied math.

My caculator says sqrt of 1.333 (1 + .333) is 1.1545561. Should I get a new one.

[Bill Kumpf]

Let's just round it to 1.15............