figure out f/stops above f/90?: nevermind

[Christopher Colley]

Greetings!

I am wondering how I would figure out (without lots of intense math) what the f/stop numbers beyond f/90 are?

my light meter goes to f/90 and I'd like to figure out the next few numbers in succession.. I understand how I'd get to the next stop after f/90 in terms of time, thats simple, but, I do not know what number I would call that stop.. or the next..

(Trying to make it easier to figure out pinhole lens exposures with nifty lables on my meter)



thanks!

edit: NEVERMIND I am a fool...... I figured it out!

 

[Ole]

The two last stops you have are 64 and 90. After 90 comes the double of 64, or 128. After that is the double of 90, or 180. And so on: 256, 360, 512, 720, 1024, 1440...

 

[Christopher Colley]

yes! thanks Ole !

I just realized this after sitting there looking at the meter for a while...

*shrugs* it was the 1 to 1.4 being one stop that confused me I think! I should have been thinking in 2 stop steps

 

[Michel Hardy-Vallée]

Here's a nice Excel sheet to calculate f-stops in increments of half or third stops:

http://www.primenet.com/~zilch0/tools.htm

 

[smieglitz]

...
*shrugs* it was the 1 to 1.4 being one stop that confused me I think!...

Or it could be the thing that sets you free. The aperture values are progressing by the square root of 2 which is 1.414... So to find any next stop just multiply the number you have by 1.4:

f/1 x 1.4 = 1.4
f/1.4 x 1.4 = f/1.96 ~ f/2 (or twice f/1)
f/2 x 1.4 = f/2.8 (or twice f/2)
f/90 x 1.4 = f/126 ~ f/128 (or twice f/64)
f/128 x 1.4 = f/179.2 ~f/180 (or twice f/90)

And if you ever need to figure ISO numbers, it is every third number in the sequence that doubles:

...25 , 32, 40, 50, 64, 80, 100, 125, 160, 200, 250, 320, 400 ... (which is approximately progressing by the cube root of 2 ~ 1.26)

Joe