"Equivalence" demonstrated: Canon 5D and Panasonic GX1

Started Apr 27, 2013 | Discussions thread
Great Bustard
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Re: You say, "An f-stop is an f-stop...
In reply to Hen3ry, Apr 29, 2013

Hen3ry wrote:

Great Bustard wrote:

Hen3ry wrote:

An f-stop is an f-stop, a shutter speed is a shutter speed, and an ISO is an ISO (although various manufacturers fudge the latter a little just as in the old days the film manufacturers fudged things a little in respect of sensitivity). So f2 @ 1/200 with a 25mm focal length lens on m43 produces an image of near enough to the same density and general characteristics as f2 @ 1/200 with a 50mm on FF.

...a shutter speed is a shutter speed, and and ISO is an ISO."  But apparently you stop short of focal length.  That is, you didn't say "A focal length is a focal length."

I find that omission curious.

That is, just as the effect of 25mm on mFT has the same effect as 50mm on FF, the effect of f/2 on mFT has the same effect as f/4 on FF.  And yet you feel "an f-stop is an f-stop" but apparently don't think that "a focal length is a focal length".

Like I said -- curious.

Oh, don’t be a silly Bustard! The curious thing is that you have written the non sequitur above.

Really?  I kinda thought that was absolutely central to what is being discussed.

The effect of focal length was implicit in what I wrote -- such as 45mm (90mm equiv).

The primary effect of focal length is viewing angle and perspective. Hence m43 45 is 35mm 90 equivalent. The aperture doesn't come into it.

Sure -- if we are only talking about AOV, the f-ratio doesn't come into it.  I've said this countless times.

DoF? Now there is where aperture matters.

Also noise.  The wider the aperture, the more light that falls on the sensor for a given shutter speed.

I’ll worry about that when I want to but basically I'm not a razor thin DoF photographer.

It may interest you to know that the f-ratio doesn't come in the form "Razor thin DOF / Super Deep DOF" -- there's a range of values.

Total light on the sensor? In practical terms, what nonsense.

In practical terms, the total amount of light projected on the sensor, combined with the sensor efficiency, determines the noise in the photo.

So, what you call "nonsense" is instead a profound lack of understanding of what role exposure and total light play in terms of the visual properties of the photo.

As I said in my post, we went through all that stuff 50 years ago when 35mm was the small format barbarian hammering at the gates. What we want is correct exposure in our given sensor size.

For that m43 f2 25mm is equivalent to FF f2 50mm.

So all we want is "correct exposure"?  I kinda thought there was more to it.  By the way, if 25mm f/2 1/100 ISO 400 is "correctly exposed" on mFT, what about the exposure of 50mm f/4 1/100 ISO 1600 on FF?  Is it "incorrectly exposed"?

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