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Forum: Pentax SLR Lens Discussion
06-02-2011, 01:40 AM
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Maybe that comes from the larger front element being able to gather more light?
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Forum: Pentax SLR Lens Discussion
06-01-2011, 11:11 PM
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I guess these days with the huge advancements in High ISO IQ the justification of such lenses is becoming harder and harder.
Does that Sigmonster come with a guarantee of perfect composition and subject arrangement?
... I think by the look of it I have my answer to the questions I had.
My conclusion is that the Max aperture merely determines how big (Diameter) and expensive your lens is.
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Forum: Pentax SLR Lens Discussion
06-01-2011, 10:27 PM
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you would need a harsher curve on the elements to bend the light yes. And there would (I guess ) be a practical limit to Front element size. but the thing that really sparked my curiosity is the Like of Leica's Noctilux 50mm f/0.95 as it goes below what I Initially thought was a '#correction: Limiting' factor of Aperture diam, not being able to get less than FL without the lens elements needing to be in occupying the same space as each other
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Forum: Pentax SLR Lens Discussion
06-01-2011, 10:04 PM
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hmm I had not seen these 200 f/2's
But I guess you answer the questions in that they just exponentially up in price
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Forum: Pentax SLR Lens Discussion
06-01-2011, 09:51 PM
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Hi guys,
I have question regarding the design restraints on max aperture of a lens. I am pretty ignorant in respect to the physics behind it so please bear with me.
I understand that that Aperture is = (FL/AD) where FL = Focal length and AD = Aperture diameter. But the reason I ask is Nikon Produce a 800mm F/5.6 thus has a AD = 142.85mm yet the fastest 200mm lens I have seen is the 200mm F/2.8 giving AD = 71.4mm.
Why can't they design a 200mm F/1.8 or faster? which would have AD=111.11mm. Is it that the lens barrel would be to large, and thus the front element being HUGE?.
Is it just not cost effective to do so or is there physical design restraints?
Any light that could be shed on the subject to calm my curiosity would be great
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