Originally posted by DaveHolmes I saw somewhere that only certain f-stops are actually 'full-stops' and that the ones between these are 3rd's of stops or half stops... can anyone confirm and if so explain?
The way I understood it to work was that these particular 'full-stops' marked a doubling of light allowed to hit the sensor as the aperture moves down towards being 'wide-open'. Is this anywhere near being correct?
Cheers
Dave
The "Full Stops" (2, 2.8, 4, 5.6 etc.) are considered the full stops. Yes, as you move from 2 to 2.8, you half the light (double it going from 4 to 2.8).
Likewise, there is a halving of the light intensity when moving from f3.5 to f5 and is a "full stop" change, although these are not considered "full stops". Mostly we use the term full stops for two reasons, first, the full stops are based off starting on f1 and then halving the light at each succeeding stop. Second, using this method of the "full stops" becomes very easy to remember. Start with f1.4 and f2 and then double every other one (f1.4, f2, f2.8, f4, f5.6, f8, f11(.2), f16, f22(.4), f32, f45 (actually 44.8) and so on.
Using the in between stops is only important when you are doing the calculations and reporting EXIF data. Otherwise you are using the information from your meter to get your exposure or going to the closest full f stop number and tweeking the exposure from there. What's 1/3 of a stop between friends anyway!
Regards,