Focal length 35mm equivalent, but not F-stop?

Started Jul 24, 2014 | Discussions thread
gandalfII Senior Member • Posts: 1,952
Re: Focal length 35mm equivalent, but not F-stop?

Beachcomber Joe wrote:

Because it is not necessary. The f stop of lenses has always been marketed and thought of as an indicator of its light gathering ability, not its depth of field. This is why we refer to lenses with wide apertures as fast, not shallow. That ability does not magically change with format. In the heyday of film and until recently in digital, photographers were ISO restricted in low light conditions. The difference of a stop of light gathering ability was a significant reason to pay the premium in cost, weight and size for a fast lens. That is how most fast lenses have been marketed and the primary reason those lenses are purchased. In many cases the shallower depth of field of the faster lens was looked upon as a negative.

Sometimes but not always the faster lens was top of the line and optically superior; eg nikkor35/1.4 and 20/2.8 were better than their f/2 and f/3.5 counterparts.  I paid the weight and cost premiums but nearly always shot them at about f/5.6.

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