Stops of light explanation

[SethAlbritton]

I understand somewhat but not fully.

F1.4 to 1.8 is a stop correct?
If so what is a stop above 1.8?

Also F1.2 is a two stops below 1.8 right?

 

[480sparky67 66]

1.4 to 1.8 is only slightly more than a half stop.

1.2 to 1.8 is one stop.

 

[Bitter Jeweler]

F-number - Wikipedia, the free encyclopedia

 

[clanthar]

1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64

 

[480sparky67 66]

1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64

3.14152653897923842643832750288.

1.73.

299,792,458

 

[clanthar]

1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64

3.14152653897923842643832750288.

1.73.

299,792,458

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610

 

[SethAlbritton]

Thanks for the help but lets make sure I still understand this

1.4-2 is a stop
2-2.8 is a stop
4-5.6 is a stop right?

Now with shutter speed
is 1/30th to 1/60th a stop
100 to 200 a stop?

Now with iso

200 to 400 a stop?

I was under the impression that when you doubled the number it was a stop, but I wasn't talking with experts either.


Thanks for the help too

 

[clanthar]

you got it! A factor of 2 -- twice as much/half as much. In the case of the lens f/stop: f = focal length / diameter of iris opening = f/stop number.

Joe

P.S. And since they're all stops they can all be interchanged without altering exposure. Add a stop with the shutter and take away a stop with the iris and exposure is constant.

 

[480sparky67 66]

1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, 45, 64

3.14152653897923842643832750288.

1.73.

299,792,458

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610

No fair! I was gonna do the Fabonacci Series!

 

[480sparky67 66]

................

I was under the impression that when you doubled the number it was a stop, but I wasn't talking with experts either.


Thanks for the help too

No. Doubling/halving the number means a two-stop difference.

 

[clanthar]

3.14152653897923842643832750288.

1.73.

299,792,458

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610

No fair! I was gonna do the Fabonacci Series!

Then do it with a photo:

photo by: Flickr: lucapost's Photostream (CC license)

Joe

 

[OrionsByte]

Thanks for the help but lets make sure I still understand this

1.4-2 is a stop
2-2.8 is a stop
4-5.6 is a stop right?

Now with shutter speed
is 1/30th to 1/60th a stop
100 to 200 a stop?

Now with iso

200 to 400 a stop?

I was under the impression that when you doubled the number it was a stop, but I wasn't talking with experts either.

Thanks for the help too

A stop is the doubling or halving of the light. For ISO and shutter speed the number used for the value can be halved or doubled, but aperture is different.

Aperture f/numbers represent the ratio of the AREA of the lens opening to the focal length. Since it's an area, you can't simply double the number and assume that is equal to twice the light. In fact, if you double the number you're actually quadrupling the light. Turns out that to double the area you multiply the f/number by the square root of two, which is roughly 1.4.

But here's a trick to help you remember. The square root of 2 times 2 IS 2. So that means every TWO stops of aperture DOUBLES the f/number. So if you can remember a couple key values like f/1.4 and f/2, you can extrapolate the rest of the values by going by two stops at a time:

1.4, 2.8, 5.6, 11, 22
2, 4, 8, 16, 32

Eventually though, you'll know them all by instinct anyways.

 

[clanthar]

................

I was under the impression that when you doubled the number it was a stop, but I wasn't talking with experts either.


Thanks for the help too

No. Doubling/halving the number means a two-stop difference.

Doubling or halving the shutter speed values and ISO values is 1 stop. That doesn't work with the lens f'/stop values. Think about the diameter of a circle. If you double the diameter of a circle it's area increases by 4.

Joe

 

[Patrice]

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610

The two first terms of the Fibonacci sequence are missing. 0,1,1,2,3,5,8......

 

[Patrice]

Are we supposed to guess?

3.14152653897923842643832750288. (the length of a half circle expressed in units of radius of that circle)

1.73. (square root of 3 rounded to two decimal places)

299,792,458 (approximate speed of light in km/hr)