Why do older camera lenses have faster F-stops?

Started Apr 14, 2013 | Discussions thread
EinsteinsGhost Forum Pro • Posts: 11,977
Re: f1.8 equivalents...

HumanTarget wrote:

EinsteinsGhost wrote:

HumanTarget wrote:

EinsteinsGhost wrote:

Only for DOF, not for exposure value.

We've been talking about exposure, not exposure value.

Exposure value has nothing to do with exposure?

I didn't say that.  I said we're talking about exposure, not exposure value (you can read it right above your post).

Why can't exposure value be discussed when exposure is?

We're disagreeing on a very basic premise: Role of "equivalent" aperture on exposure.

Brightness Value of a Scene = Aperture Value + Time Value - Speed Value (ISO)

Aperture Value is NOT based on the idea of equivalent aperture. For that matter, if you took a light meter for a scene and observed ISO 100, 1/1000s at f/2.8 for a scene, what adjustments would you make for a camera with a smaller sensor? Use an m4/3 sensor to keep it simple.

The f-number system is not based on equivalent aperture, no, and that's what makes it so easy and convenient to use.  But we have not been talking about that, we've been talking about the actual amount of light hitting the sensor, which is necessary when discussing equivalence.

Useless for comparing exposure.

Actually determining exposure is useless in comparing exposure?  Explain how this is so.

So you understand what makes up exposure, when you are comparing them.

If you want to capture the same image (in terms of DOF and shutter speed) on two differently-sized sensors, the larger sensor must have a proportionally higher ISO.  But the two will receive the same amount of light (the same exposure).

Thank you for stating my point.

A higher ISO does not change the exposure, so I don't see what you're trying to say.  What exactly is your point?

Higher ISO is needed to match the exposure.

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