2More Q's. ^^ - ISO, Angle of view.

[Innocence]

Dearest All,

hee hee.

1/ Angle of view on a lens specification, is that exactly what I think it means? And what does the diagonal angle of view mean?
e.g. off the specs of the 20-70 /f2.8L
Diagonal Angle of View :

74˚ - 29˚ (43.2mm)

Haha, what on earth is the range?
I find it easier to visualise how "wide" a lens is in terms of it's angle, but I'm not sure what I'm looking at.

2/ Is there some sort of conversion (an equation maybe?) that relates ISO increases and how much um, better it will work in less light?
Or does the question not make sense? e.g. f/2.8 -> f/4 = half the light.
Is there something like that wrt ISO?
And is there a reason ISO goes up in doubles? Or am I mistaken haha.

Thankees!

 

[Rob]

1. I've not particularly seen diagonal fov before? It's not a measurement which makes sense to me... perhaps someone else can answer this one.

2. Yes. ISO 100 is the "normal" amount of light sensitivity, 200 is double the light sensitivity, 400 quadruple the sensitivity etc... So f2.8 at 100 ISO is the same exposure as f4 at 200 ISO - stops are doubling of light and ISO goes up in the same way to be convenient.

Make any sense?

Rob

 

[Innocence]

haha yes, thank you rob, that makes perfect sense.

hope someone can have a stab at Q1.

 

[Unimaxium]

Diagonal angle of view is the measurement in degrees of the diagonal of the image rectangle, as opposed to its width and height. The reason it's a range in that example is because it's for a zoom lens.

 

[Rob]

I guessed it would probably be corner to corner, but why would you want/need to know it?? :S

Rob

 

[Unimaxium]

Why not? Why are computer monitor sizes measured in terms of their diagonals?

 

[Torus34]

To make them seem larger than thery are. Can you think of another reason?