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06-02-2008, 11:01 AM   #1
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The "real" values for the FA 77mm f/1.8 Ltd. Just out of curiosity.

I faintly remember seeing somewhere that the measured focal length and the true aperture value of this legendary lens were slighltly different than specified. However, my searches did not help me find that piece of information again.
The focal length was closer to 80mm and the maximum aperture was to 2.

Is my memory playing tricks on me or what?

(I adore this lens, no matter what the numbers say).

06-02-2008, 11:07 AM   #2
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maybe the one made in Burma?
06-02-2008, 11:59 AM   #3
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In the Popular Photography review of DA* 200mm f/2.8 they have measured the focal length as "198.33mm", for example. For the FA 50mm f/1.4 they report "51.93mm, f/1.45".
They did not tell whether those were made in Burma. :=)
06-02-2008, 12:53 PM   #4
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Whats the point of making the lens 77mm if its not 77mm?

I can see the 70mm not being exactly 70mm, but why decide on crazy numbers like 31mm, 43mm and 77mm if they were not that focal length?

06-02-2008, 02:42 PM   #5
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Part of the issue is that the focal length is measured at infinity. As you focus closer the actual focal length becomes longer and the effective f stop changes to let less light hit the sensor. So, perhaps Pentax designed the lens to be 77mm at infinity and test labs measure at... ummm... let's say 50 feet. That may account for the difference. Just a guess.
06-02-2008, 03:51 PM   #6
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(77mm is approx half way between 70mm and 85mm... )
06-02-2008, 05:34 PM   #7
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QuoteOriginally posted by bc_the_path Quote
I faintly remember seeing somewhere that the measured focal length and the true aperture value of this legendary lens were slighltly different than specified. However, my searches did not help me find that piece of information again.
The focal length was closer to 80mm and the maximum aperture was to 2.

Is my memory playing tricks on me or what?

(I adore this lens, no matter what the numbers say).
your mind is not playing tricks with you. i've read many many posts on these lenses to make my decision.

Godfrey says here that the lens is longer than 77mm
Should I get 77mm or 70mm? - Photo.net Pentax Forum

the f2 remark, i haven't heard, but this post does mention the DA70 is closer to 2.8
Digital SLR and Lens Review: By popular demand: Pentax DA 70mm Limited compared to FA 77mm

now if i could only take as good photos as i am at scrounging around and reading
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