it seems that we just naturally gravitate towards certain focal lengths; even with a zoom, we tend to choose prime focal lengths more so than we choose non prime.
I always find it interesting to look at the focal lengths of my photoshoots, I find it amazing just how often they do gravitate towards primal focal lengths. But then again, there are lies, damned lies, and statistics!
Few would debate that there are certain focal lengths that work well for certain types of shots. But my original question was really about why the standard focal lengths are PRECISELY 24/35/50/85mm, and not +/- 5mm off of those lengths.
They are not precisely 24/35/50/85 .... they are just labelled that way by the manufacturer for easy marketing I suspect. They are all off by a bit. Zoom ranges can be quite a bit off.
Good point! And that begs the question even further. A few possible scenarios...
1. There are true "standard" focal ranges (e.g. +/- 2mm) around the 24/35/50/85 marks; and, for marketing purposes they have always rounded to a number that sounds good.
2. There are no inherent or intrinsic "standards" and everything is just a product of arbitrary historical precedent.
Personally, I think the standards are arbitrary. Great shots can be had at any focal length.
I think the reason why people accept the standards (and some believe they are baked into the fabric of life) is that they do serve successfully as guides for choosing lenses and composing shots. But it would seem to me that in a parallel universe (or by quirk of history)... 22/32/46/80 could just as easily be the standard focal lengths.
On a side note, I should point out that the most commonly used focal lengths (35mm equivalent) are probably...
Samsung Galaxy S III: 26mm
iPhone 5: 33mm
iPhone 4s: 33mm
iPhone 4: 29mm
HTC One: 27.54mm
From this we can see how marketing departments might be tempted to round up or down to 28mm and 35mm. Certainly "27.54" has a bad ring to it. And if rounding up or down by 0.5 is no sin, then surely rounding by .75 or even 1.75 is no sin either! ;-)