- Aug 23, 2012
- Denver, Co
- Real Name
- Sean Rastsmith
Yes, the larger the focal length the bigger the pupil at the same fstop. Hence my 45/75 example. Nothing to do with what it was designed for. The reason people dont mention it is that it is redundant. Any given focal length and fstop means the enterance pupil is x. If you change one, x changes. This is true no matter the sensor designed for. The reason a speedbooster doesn't work is twofold. One is that the image circle cant be compressed without vignetting. The other is that there is no room to add to the flange distance without losing infinity focus.I think we are saying the same thing. I never said aperture is related to sensor size.
25 / 1.4 = 17.85
50 / 1.4 = 35.71
So I think the 50 mm "pupil" is bigger than the 25 "pupil" and this means that more light pass through, is this correct? So when I set the 50 to 1.4, on the same MFT body, I'm letting in more light (even if a lot of it does not reach the sensor).
So when someone says that the 25 is equivalent to a 50 angle of view he's saying a correct thing. But he also should say that the "pupil" is smaller if compared to the pupil of a real 50mm. Is this correct? I mean, it's no big deal, I think it's quite obvious. Am I wrong?
Of course the picture brightness does not change, but I'm not talking about exposure here.
About the speedbooster see my first post: I think we are telling the same thing. So you cannot make a speedbooster for an MFT lens on a MFT body because there is not extra light spread around.
I agree. But the Minolta 90mm at the same aperture will have a pupil twice the 45.
The 12-35 second example is wrong. He will get the same FoV as a 24-70 lens while still having the same fast shutter speeds allowed by 2.8 at the same ISO. He is getting a 2.8 lens. Nothing impied the guy wanted the DoF of a 24-70 lens at 2.8, but this guy told us that is what he wanted to make a point.
.The problem is the guy takes the thoretical noise to sensor ratio as given even though all sensors behave differently. A 16mp 35mm sensor would have each pixel being 4x the size of a 16mp 4/3 sensor, if built the exact same, or it would need to be a 64mp sensor to be perfectly upscaled. ISO works and has for a while. He is trying to compare s-n ratio in a theoretical sense, the taking that assumption, along with equivalent dof and applying to all of the rest of the things.
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