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04-03-2021, 10:19 AM   #1
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the reason for the original Limited focal lengths

somewhere, in my memory, from the 90s or so, there were stated Pentax reasons for choosing 31, 43 and 77 for the focal lengths of their Limited lenses. And I cannot recall or find them. It might have had something to do with angle of view compared to human vision. Anybody remember?

04-03-2021, 10:51 AM   #2
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The 43mm corresponds to the diagonal across the 35mm/FF frame, that much I remember. I forget the justifications for the other two, though from my own personal experiences the 77mm is MUCH a easier walk around FF than 85mm.
04-03-2021, 11:12 AM   #3
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QuoteOriginally posted by tvdtvdtvd Quote
The 43mm corresponds to the diagonal across the 35mm/FF frame, that much I remember. I forget the justifications for the other two, though from my own personal experiences the 77mm is MUCH a easier walk around FF than 85mm.
The 43mm is almost exactly the angle of the human eye view. The 3:2 ratio of the first film format is anything but random too. No wonder maths agree with that. I would really love to know about the other two lengths, they are peculiarly unrelated...
04-03-2021, 11:14 AM   #4
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The interesting decisions behind focal lengths of the 43 and 77 Limiteds are discussed in the paper referenced in this thread: Lens Technical & Trial Use Reports. SMC Pentax FA77mm and FA43mm. Hirakawa Jun & Adachi Masamitsu (2000)
(download 1.87 MB)

04-03-2021, 12:57 PM - 3 Likes   #5
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I seem to recall they were chosen based on occult numerology and Ouija boards were possibly also involved.
04-03-2021, 01:50 PM   #6
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QuoteOriginally posted by Gray Quote
The interesting decisions behind focal lengths of the 43 and 77 Limiteds are discussed in the paper referenced in this thread: Lens Technical & Trial Use Reports. SMC Pentax FA77mm and FA43mm. Hirakawa Jun & Adachi Masamitsu (2000)
(download 1.87 MB)
This ^ ^ ^

Also...this:

https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/396940-fa-...a-limited.html


Steve

(...now, about that frame diagonal...)
05-26-2021, 03:49 PM   #7
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Someone made a convincing point in another thread I read just yesterday (but can't remember or find who and where that was said) that the focal lengths of the FA Limiteds lie (almost) right in between other popular / "standard" focal lenghts:

28+35 = 63 / 2 = 31.5 -> 31
35+50 = 85 / 2 = 42.5 -> 43
50+105 = 155 / 2 = 77.5 -> 77

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