A few words on Equivalence and comparing systems

Started Apr 2, 2013 | Discussions thread
Macx
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Re: A few words on Equivalence and comparing systems
In reply to Alumna Gorp, Apr 3, 2013

Alumna Gorp wrote:

Macx wrote:

I understand the point of thinking about lenses in focal lengths and focal ratios, but for the purpose of comparing lenses for one system with lenses for another system, it would be much better to talk about what angle of view (or field of view) the lens is providing and the physical size of the aperture. It really cuts through to what is important with regards to framing, perspective, depth of field, diffraction and light, and the argument that "Angle of view = angle of view" and "Physical size of the aperture = physical size of the aperture" are easy to grasp.

Two systems using lenses that each provide the same angle of view and with the same physical size of the aperture are equivalent.

And I think that as we're finally moving towards a new paradigm of what the goal of exposure is in digital photography, the old idea about "f/2.8 is f/2.8" might also be slowly on the way out.

Why would or should the thoughts that a 2.8 is a 2.8 be on the way out, its always`s been this way, take medium format v 35mm there both very different but I can`t say I have ever come across anyone who has concerns over dof, its just something you live with or get over

For me a 2.8 is a 2.8, it always will be, dof may be different that`s for sure, you adapt, adjust and get on with it, its not a problem for most of us in the real world of things.

But calling a 2.8 a 5.6 or what ever is being a bit over the top and makes no senses at all.

Well, what is it? Is it important what f/2.8 means or not?

I completely understand that for some people, this isn't important. As you wrote, they'll shrug their shoulders and adapt as well as they can. But knowing about how these things work can still help you understand how to use your gear to better in a creative way too. And besides, these things usually only pop up when people are deliberately compairing lenses for one system with lenses for another system. In these cases, this knowledge is useful.

Why I think that "f/2.8 is f/2.8" is on the way out is that in digital photography there is a new way of thinking about getting the right exposure which isn't about matching shutter, aperture and ISO to get the right brightness in the photo, but is about getting the best noise performance for the aperture and shutter time you've chosen. In this context it means that the important thing your chosen aperture decides is the depth of field and the total light it will provide. Gollywop made a very good thread about this that summed up most of the changes to how we think exposure in digital (raw) photography, and I would encourage you to look it up if you are at all interested in it.

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