Comparing Olympus 4/3lenses to FX "Full Frame" offerings

Started Jan 25, 2014 | Discussions thread
Great Bustard Forum Pro • Posts: 40,567
Re: Tired of hearing this fallacy about fstop equivalence.

veroman wrote:

Doctor Lecter wrote:


"While crop factor has a use simply to compare focal lengths between formats and such, the constant comparison of a smaller format lens to its full frame ‘equivalent’ aperture is largely unevenly applied and misunderstood. It’s often used to show that a smaller format is inferior or not capable of the same things as a larger format. In some cases, this usage is correct, but it is also nearly never used the other way.

I’ve heard many times “Yeah, your 75mm f/1.8 is crap – it’s like a 150mm f/3.6.” No, it’s not, it’s a 75mm lens with an f/1.8 aperture and a field of view that is the same as a 150mm lens on full frame.

What IS true is that the 75mm f/1.8 is not capable of the same ultra shallow depth of field as, say, something like the Sony Zeiss 135mm f/1.8 on full frame. However, this is essentially the ONLY way that it is inferior. It passes the same amount of light, and it exposes as an f/1.8 lens because it IS an f/1.8 lens"

I'm tired of hearing it, too.

Many religious are tired hearing about Evolution, too.

He tried it with me a few posts ago. I simply stopped arguing the issue. As I said in my post, f/2.8 is f/2.8 whether applied to 4:3, full frame, APS-C, a point and shoot, medium format or an 11 X 17 view camera. Other things come into play, for sure. But aperture is a constant.

As I said, f/2.8 is f/2.8 in terms of exposure (light per area on the sensor) but not in terms of the total amount of light projected on the sensor.  It makes a difference, you know, and a rather large one.  Pity you, and others, actively choose to argue against such a simple fact.

My Canon 85mm f/1.8 is f/1.8 on my crop 40D and is f/1.8 on my full frame 5D. If this weren't so, none of us would ever know exactly what we're purchasing or what settings we're shooting at!

And that's right at the heart of the matter when so many ignorantly exclaim that the DOF of larger formats is "too shallow" and that larger formats have less noise.  You see, the diameter of the aperture relates to both DOF and the total amount of light projected on the sensor, and thus the noise.  So larger formats gain their noise advantage over smaller formats by using a more shallow DOF for a given shutter speed.

Of course, choosing to remain ignorant over that fact is always an option, and, I might add, a rather popular one.

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