Hi... was puzzled on how people calculate f-stop value?
For example a f5.6 + 2 stops equals to wat no.? what is the formula used?
Hi... was puzzled on how people calculate f-stop value?
For example a f5.6 + 2 stops equals to wat no.? what is the formula used?
When people say '+' I usually think to open up, not stop down. So my answer would be f2.8. You should clarify your '+' is to let in more or less light, cheers.
eyes | head | feet | flickr | APAD: straight from camera
Then there's stuff like 1/2 stops or 1/3 stops in camera settings, which makes it even more confusing.
If I'm not wrong, for 1/3 stops, it goes something like this: (correct me if I'm wrong)
f1, 1.1, 1.2, f1.4, 1.6, 1.8, f2.0, 2.2, 2.5, f2.8, 3.2, 3.5, f4, 4.5, 5.0, f5.6, 6.3, 7.1, f8, 9, 10, f11, 13, 14, f16, 18, 19, f22
Garion, I was reading and following this thread. Your this information is very enlightening to me. I have never thought of it in such an exact way. Thank you.
I have a question here: do these terms 'increase by 1/3 stop, 1 stop, 2 stops' appply to , say, shutter speed and ISO too?
eyes | head | feet | flickr | APAD: straight from camera
actually just rem the FULL stops can liaoz.. 1/2 stops usually not necessary and typically only "occur" if you use AUTO.
Basically F stop number is focus distance / diameter of aperture
This math works in a way which if you increase a stop, the diameter of the aperture doubles and more light enters.
Example f1.4 - F2.0
This is also the reason why photographer uses stop for exposure. Increase 1 stop of light means double the amount of light.
To put it in a physical context, everytime you go UP a stop, you are letting in twice as much light (with regards to aperture or shutter speed).
That is, you are opening the shutter twice as long (1/30s --> 1/15s) or doubling the size of the aperture (f/2 --> f/2.8)
ahhh, but why 2 --> 2.8? Shouldn't it be 4?
the formula for area of a circle is PI - r squared. [secondary, or was it primary school maths?]
Multiply PI x 2(squared) vs PI x 2.8(squared) and one result is double the other.
So the diameter (or radius, no difference in this context) of the circle increases by a multiple of approximately 1.4, but the area of the circle doubles.
hope that helps.
Exploring! :)
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