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02-21-2014, 12:55 PM   #31
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QuoteOriginally posted by Na Horuk Quote
Its a whole science
I agree with most of what you have said, but - with all due respect - not this one. I should say lens making is an ART!

It is more like cooking: You know the basic ingredients for a certain meal, but one chef makes it differently from another and results are never quite the same.

Just to illustrate Na Horuk's points about lens designs, I have attached two lens diagrams (FA 50mm f/1.4 and Tamron 01B 24mm f/2.5). It is quite obvious that even "simple primes" aren't that simple after all.

One may note that the entrance pupil of the FA 50mm is 36mm in diameter while the Tamron 24mm has an entrance pupil of 9.6 mm even though the TAMRON has a filter thread of 55 mm while the PENTAX has a "mere" 49mm. See attached photo.

Generally speaking: Making VERY large lenses is costly because it is difficult to cast large specimens without flaws. Making small may be cheap in glass but very demanding in respect of shaping and associated tolerances required.

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02-21-2014, 01:06 PM   #32
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QuoteOriginally posted by jon404 Quote
@jogiba -- that is a very interesting picture! Unless I'm wrong, all four lenses are designed to cover a FF sensor. And, as I've learned from this thread, they all produce the same exposure at, say. f/2.8.

So why is the Sigma lens glass so large? As another post noted, lens designers certainly aren't stupid. Off the top, I'd think that the larger glass must cost more to produce that the smaller glass on the other lenses. Is that true? If so -- what optical advantages do they get, if any? Or, is it just a marketing thing aimed at folks like me -- "bigger lens, must give you better pictures?"
A lot has to do with how corrected a lens is and how sharp wide open. A lens like the FA 50 f1.4 may give the same exposure wide open as the Sigma 50mm f1.4, but it will be a lot softer, particularly in the corners. Stopped down a stop or two, you might not be able to tell the difference.
02-21-2014, 07:44 PM   #33
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Thanks Na, Stone, and Rondec -- what an interesting business! And the more you learn about it, the more fascinating it gets. Perhaps many areas are like this -- automotive design comparisons, or software differences between programs that seem similar but each having some key selling point.

As an consumer, I'm glad that capitalism has prevailed over communism and fascism. It may be silly to have so many competing similar brands, but it sure is fun! And it seems to make for a lot more jobs, even if people are basically making basically the same thing at different enterprises...
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