I know exactly now, what f-stop means and how it is calculated. Basically, f-stop is a focal ratio, which equals focal length divided by aperture diameter. This explained to me, why the bigger is F-number, the less light is getting through the aperture.
The full exposure step is a square root from 2. Most of modern cameras use 1/3EV, which comes together with ISO standard. I checked and it appeared the same for my Nikon D40. At least I know now, what this 1/3 EV means.
As for aperture diameter meaning. Keeping it simple, aperture determines, how many rays of light reach the sensor. With wider aperture object in front is in focus and background is blurred. This is a good thing to know, when taking macro pictures.
Shutter speed determines the time aperture is open.
So, basically there are two parameters that determine everything - the size of the 'hole' and the time 'hole' stays open to get the light. Depending on which parameter you change, the other parameter is being adjusted to another. In other words, you can get the same result either by changing the 'size of the hole' or 'the period, while hole stays open'.
I hope, I am not too confusing...
As regarding my camera Nikon D40 and lenses, the parameters I have learned now, are:
- Exposure step = 1/3EV
- Sensor size = 23,7 x 15,6, which equals to most modern cameras ratio 4:3
- Tamron lens: f-number = 3.5 till 6.3; Focal length 18 - 250 mm, which gives angle view range from 100 to 10 degrees.
- Tokina lens: f-number = 4; Focal length 12 - 24 mm, which gives angle view range about 118 to 84 degrees.
Considering sensor size, the angles of both my lenses should be multiplied by 1.5 (crop factor), which will give the actual angle that lenses cover.