01-08-2015, 06:43 AM
Scythels, the new 300/4 is exactly 75 mm shorter than the old one. I'm sorry, I don't want to defend BC's often weird posts but sometimes he happens to hit the nail even with false assumptions 
As far as I understand this fresnel stuff, it's the same geometry that makes the optical systems of a lighthouse work or the old fresnel screens in analog cameras or those flat loupes or "wide angle" lenses on some rear screens of buses work. All those systems have in common "lightweight" and "short lens length" and, if saving money was the reason to make this reading loupes, the quality usually is better than a plastic loupe with spherical elements and worse than one with grinded and polished glass. I think, the manufacturing process of this fresnel stuff is quite tricky.
Apparently this PF element appears to make the lens shorter by quite a strong bit (⅓) and lighter by nearly 50%. You can write a scientific book about why this is not caused by the PF element. Alone. But it contributes to it. As for the weight reduction, this is also based on massive use of (high-tech) plastics (maybe the PF element is also made of plastics?) and the electronically driven aperture and focus drive.
Still, it's impressive enough.
As far as I understand this fresnel stuff, it's the same geometry that makes the optical systems of a lighthouse work or the old fresnel screens in analog cameras or those flat loupes or "wide angle" lenses on some rear screens of buses work. All those systems have in common "lightweight" and "short lens length" and, if saving money was the reason to make this reading loupes, the quality usually is better than a plastic loupe with spherical elements and worse than one with grinded and polished glass. I think, the manufacturing process of this fresnel stuff is quite tricky.
Apparently this PF element appears to make the lens shorter by quite a strong bit (⅓) and lighter by nearly 50%. You can write a scientific book about why this is not caused by the PF element. Alone. But it contributes to it. As for the weight reduction, this is also based on massive use of (high-tech) plastics (maybe the PF element is also made of plastics?) and the electronically driven aperture and focus drive.
Still, it's impressive enough.