why not f/1.2 by Sony?

Started May 14, 2013 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: that's not a fast lens

franzel wrote:

tko wrote:

Don't know why people call this a fast lens.

F1.2 35MM = F1.8 50MM (there is a reason the OP picked those numbers.)

There is a single reason why a lens with a wide max aperture is called fast - it allows for a higher - faster - shutter speed at the same ISO, to help avoid camera shake or freeze fast moving objects .
It also provides a brighter finder image for SLR cameras, and helps to focus more precisely .

And you forgot one key factor that plays a role: Sensor Size. No, I'm not talking about f/1.2 becoming f/1.8 or vice versa, but the fact that you're going to be more limited with ISO choices with smaller sensors than with larger.

A 35/1.2 lens on APS-C sensor... what exactly would it accomplish over 35/1.8 outside of bragging rights?

Shallow DOF is only a side effect, and can be used as a photographic effect if desired, but is not the reason 'fast' lenses were being introduced originally .

It is not a case of "if desired" for a portrait lens. It is a characteristic expected of a portrait lens.

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