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06-01-2011, 09:51 PM   #1
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Max Aperture Design Limitations

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

06-01-2011, 09:58 PM   #2
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Canon & Nikon have 200mm f2 lenses for around $6k while their 200 f2.8's are $1k or less. So 1 stop is $5k or 6* the price. I guess f/1.8 is possible but that might end up being a $12k lens, probably no market for it....
06-01-2011, 10:04 PM   #3
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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
06-01-2011, 10:06 PM   #4
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If you think about it, if you hold the front element size constant (or nearly constant), you're going to have to bend the light more accutely the shorter the FL you go. That sounds like a limiting factor to me.

However, I may be wrong - it may just be a marketing decision.

06-01-2011, 10:26 PM   #5
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How I lust after the Nikon 200/2...

:drool:
06-01-2011, 10:27 PM   #6
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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
06-01-2011, 10:46 PM   #7
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I remember back around the turn of the millenium I used to run the sidelines at Ballymore Rugby Union matches. I was using my FA 200/2.8, but there was a Canon lad there with one of those 200/1.8, and a 400/2.8 hanging around his neck. Damn impressive chunk of glass to see in the flesh.



Canon also had a 50mm/F1.0 I believe.

All's possible with untold wealth at ones disposal..

Look at the Sigma 200-500/F2.8 for example... Got a spare $32000.00 hanging around. Google it, pics of guys holding it like a trophy fish. Its a monster!!!
06-01-2011, 11:11 PM   #8
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QuoteOriginally posted by cmohr Quote
I remember back around the turn of the millenium I used to run the sidelines at Ballymore Rugby Union matches. I was using my FA 200/2.8, but there was a Canon lad there with one of those 200/1.8, and a 400/2.8 hanging around his neck. Damn impressive chunk of glass to see in the flesh.



Canon also had a 50mm/F1.0 I believe.

All's possible with untold wealth at ones disposal..

Look at the Sigma 200-500/F2.8 for example... Got a spare $32000.00 hanging around. Google it, pics of guys holding it like a trophy fish. Its a monster!!!
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.

06-01-2011, 11:47 PM   #9
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One thing did puzzle me about all this max aperature business, we where both using the same exact film, 800asa fuji, both shooting 200mm, both at f4, yet his shutterspeeds were infact quicker??? So with a lens with a greater max aperature, was is it in fact letting more light thru even when stopped down to the same aperature setting as mine????
06-02-2011, 12:09 AM   #10
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QuoteOriginally posted by cmohr Quote
One thing did puzzle me about all this max aperature business, we where both using the same exact film, 800asa fuji, both shooting 200mm, both at f4, yet his shutterspeeds were infact quicker??? So with a lens with a greater max aperature, was is it in fact letting more light thru even when stopped down to the same aperature setting as mine????
f-stop is not a T-stop
06-02-2011, 12:24 AM   #11
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Yeah, I do get that, but would have thought that the Pentax FA 200/2.8 lens elements would be similarly on par with the Canon elements in the EF 200/1.8 as far as transmission goes, and 1/2 stop quicker maybe, but I was shooting around 1/100th, and he was upwards of 1/400th - 1/640th, we were both under 1/3ev. Oh well, there you go.
06-02-2011, 12:36 AM   #12
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QuoteOriginally posted by Chaos_Realm Quote
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
i saw that lens, it's hilarious, why would anyone want to carry it around is beyond me. let alone trying to get 6k to buy it.
06-02-2011, 12:56 AM   #13
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Canon also did a 50mm F0.95 for the Canon 7 RF

Kim

QuoteOriginally posted by cmohr Quote
Canon also had a 50mm/F1.0 I believe.
06-02-2011, 01:40 AM   #14
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QuoteOriginally posted by cmohr Quote
Yeah, I do get that, but would have thought that the Pentax FA 200/2.8 lens elements would be similarly on par with the Canon elements in the EF 200/1.8 as far as transmission goes, and 1/2 stop quicker maybe, but I was shooting around 1/100th, and he was upwards of 1/400th - 1/640th, we were both under 1/3ev. Oh well, there you go.
Maybe that comes from the larger front element being able to gather more light?
06-02-2011, 02:27 AM   #15
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QuoteOriginally posted by cmohr Quote
Yeah, I do get that, but would have thought that the Pentax FA 200/2.8 lens elements would be similarly on par with the Canon elements in the EF 200/1.8 as far as transmission goes, and 1/2 stop quicker maybe, but I was shooting around 1/100th, and he was upwards of 1/400th - 1/640th, we were both under 1/3ev. Oh well, there you go.
that is quite a difference...maybe also dependant on calibration of exposure system if he was using multi-segment metering
I`d also say that such expensive lens gets better element coating with higher than average transparency (no proof though)
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