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Re: new Metabones adapter gives nex crop factor higher-quality full frame look.
In reply to El Matadurr,
4 months ago
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El Matadurr wrote:
Hye wrote:
El Matadurr wrote:
Taking a supposed 10mm lens with a 20mm front element, the f-stop would be f/2. If this adapter reduces the focal length, so now the 10mm lens is now 5mm (or whatever the value is), we get 20mm/5mm, or f/4.
You're a slightly off (see http://en.wikipedia.org/wiki/F-number#Notation):
f-number is focal length / aperture diameter, but the f-number is expressed as f/X, where X is the previously calculated ratio.
So in your example, with focal length 10mm, and diameter 20mm, the f-number is 1/2, which would be expressed as f/0.5, not f/2.
Decreasing the focal length to 5mm then gives you f/0.25, not f/4.
HTH
Thank you, that clears it up, but it still begs the question, how is an attachement behind the lens allowing more light to hit the sensor?
Is it because of this: with the adapter's element catching all the light from the rear element, it focuses it all at the smaller APS-C circle, whereas that light without the adapter would cover all around the sensor as well, thus light "lost"?
You are over thinking this. Adding another lens element, in the adapter, changes the focal length of the lens.
Aperture is merely defined as lens focal length/lens diameter. So by reducing the lens focal length, you also reduce the aperture, making the lens faster.
A tele converter does the opposite, making the lens slower.
Problem with converters has always been IQ, or lack thereof. Because the lens is added between the exit of the lens and the sensor, it can cause all sorts of side effects.
But I applaud Metabones, the thought of taking a FF lens and compressing it into a DX lens is a clever one.
--
Cheers,
Henry
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