Full frame lens is significantly cheaper than smaller format lens

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bob13bob Regular Member • Posts: 321
Full frame lens is significantly cheaper than smaller format lens
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Source for the below: https://www.dpreview.com/articles/2666934640/what-is-equivalence-and-why-should-i-care

There is a lot of misunderstanding on this topic. Consider reading the above article, but i’m providing a cliff’s notes below.

Equivalents

Focal length is not a good measurement, it’s dependent on sensor size; what we’re really looking for is Diagonal angle of view.

FF: 24.4 angle = nominal 100mm FL = FF equivalent 100mm

Mft: 24.4 angle = nominal 50mm FL = FF equivalent 100mm

Aperture F stop is also dependent on nominal Focal Length which is dependent on sensor size. The smallest the sensor, the smaller nominal focal length you will have. A better measurement is Aperture Diameter for how much light is collected. AD is not perfect; talk about that later.

FF @ FF 100mm equivalence. AD 25mm = nominal f4. = FF equivalent f4

Mft @ FF 100mm equivalence.AD 25mm = nominal f2 = FF equivalent f4

Yes, a FF 100 f4 lens collects 4x as much light as a mft 50mm f4. FF equivalents will be 2 fstops more than mft.

Instinctively, people have realized this. There is reason $150 pocket cameras can come with a nominal “F2” lens when FF f2s lens alone cost twice as much. How can such a tiny lens collect as much light, and therefore be as fast? It’s not, that’s because that nominal F2 tiny camera, is FF equivalent F11 in terms of AD.

Even F stop among two different FF focal lengths are very different.

FF 100mm f4 = AD 25mm

FF 50mm F4 = AD 12.5mm.

Pi*r^2 formula. The 100mm actually has to let in 4x as much light; it’s aperture is 4x as large in order to achieve the same light intensity on the sensor aka iso. It collects a much smaller cone/sliver of light, so needs a bigger AD or pupil to do it. This is why lens get a lot bigger the longer FL they have while having the same “

F-stop”

A FF at iso 100 collects 4x the light vs MFT at iso 100. That is why FF400 is roughly same quality as MFT iso100 (proven in link). In other words, 1 sq mm of MFT is responsible for generating the same amount of image as 4 sq mm of FF. even at iso 100, larger sensors produce better images than smaller sensors. But the “acceptable bar” becomes more defined at low light with higher nominal isos.

Diffraction. Do smaller sensors have an advantage to achieving larger dof before diffraction kicks in. No, because diffraction and DOF actually depend on equivalent aperture or FD, not nominal aperture. The mft 25mm has the same DOF limits as the FF 50mm. If that is mft nominal f8, it would be ff nominal f16.

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