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08-07-2008, 08:32 AM   #1
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FA Limited Lens' focal length question

I am curious about how Pentax came up with the focal lengths for the three FA limited lens - 31, 43 and 77 - How do they decide on these focal lengths ?- why not, for example, 30-50-75?


Thanks

08-07-2008, 08:45 AM   #2
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QuoteOriginally posted by VAV Quote
I am curious about how Pentax came up with the focal lengths for the three FA limited lens - 31, 43 and 77 - How do they decide on these focal lengths ?- why not, for example, 30-50-75?


Thanks
I'm not sure about the 31mm and the 77mm, but 43mm is the "true normal" perspective for 35mm film. That's because 43mm is exactly the diagonal length of 35mm film. With the 1.5x crop factor of APS-C sensors that probably makes a 28mm the "true normal" for our DSLRs.
08-07-2008, 09:00 AM   #3
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QuoteOriginally posted by VAV Quote
I am curious about how Pentax came up with the focal lengths for the three FA limited lens - 31, 43 and 77 - How do they decide on these focal lengths ?- why not, for example, 30-50-75?


Thanks
pentax is weird, questioning their focal length choices is like asking a man on crack what he thinks of green waterfalls.

just accept it and move on, hahaha.
08-07-2008, 09:46 AM   #4
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QuoteOriginally posted by VAV Quote
I am curious about how Pentax came up with the focal lengths for the three FA limited lens - 31, 43 and 77 - How do they decide on these focal lengths ?- why not, for example, 30-50-75?


Thanks
There is a story circulating around (somewhere in the wilds of the web) that the ltd's were originally a private project of Pentax's senior design engineer. It seems that he was an avid amatuer photographer, and those were the focal lengths he liked the most. The lenses weren't designed for production, but after seeing how well they performed Pentax was convinced to produce them commercially.
I have searched but I cannot find where I originally read the above, probably somewhere in the bowels of DPR, but it's a cute story none the less.

NaCl(the other response is "occult numerology" )H2O

08-07-2008, 10:24 AM   #5
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QuoteOriginally posted by JJJPhoto Quote
I'm not sure about the 31mm and the 77mm, but 43mm is the "true normal" perspective for 35mm film. That's because 43mm is exactly the diagonal length of 35mm film. With the 1.5x crop factor of APS-C sensors that probably makes a 28mm the "true normal" for our DSLRs.
Thanks for the response JJJPHoto.. I didn't know 43mm is the diagonal of the 35mm film. But isn't 50mm usually considered to be the 'normal perspective' of our vision?
08-07-2008, 10:25 AM   #6
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QuoteOriginally posted by VAV Quote
Thanks for the response JJJPHoto.. I didn't know 43mm is the diagonal of the 35mm film. But isn't 50mm usually considered to be the 'normal perspective' of our vision?
50mm is also the carl ziess design from a long time ago....
08-07-2008, 10:30 AM   #7
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QuoteOriginally posted by NaClH2O Quote
There is a story circulating around (somewhere in the wilds of the web) that the ltd's were originally a private project of Pentax's senior design engineer. It seems that he was an avid amatuer photographer, and those were the focal lengths he liked the most. The lenses weren't designed for production, but after seeing how well they performed Pentax was convinced to produce them commercially.
I have searched but I cannot find where I originally read the above, probably somewhere in the bowels of DPR, but it's a cute story none the less.

NaCl(the other response is "occult numerology" )H2O
Nice little story
08-07-2008, 11:07 AM   #8
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QuoteOriginally posted by VAV Quote
Thanks for the response JJJPHoto.. I didn't know 43mm is the diagonal of the 35mm film. But isn't 50mm usually considered to be the 'normal perspective' of our vision?
50mm is used as a standard because it was cheaper to produce a high quality lens with minimal distortion "back in the day" if it was 50mm rather than just a little wider at 43mm.

The idea that 50mm is the normal perspective of the human eye is just an urban legend/myth that has been debunked many times in print, online, and even on TV. The actual normal perspective for the human eye is technically MUCH wider ... as in extreme wide angle ... but our brains interpret perspective in relative terms (which is why sometimes you focus on tiny details like a macro lens and sometimes you look at a huge landscape like a 8mm lens with almost no distortion.

http://www.assassinationscience.com/johncostella/physics/A%20beginners%20gui...0of%20view.pdf

In any case, "true normal" perspective in photography is based on the diagonal measure of the film plane or image sensor ... which is why 80mm is the standard for medium format film.

It has nothing to do with what the human eye sees ... but rather the math involved with calculating the ideal perspective for the imaging surface.

08-07-2008, 11:11 AM   #9
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QuoteOriginally posted by JJJPhoto Quote

The idea that 50mm is the normal perspective of the human eye is just an urban legend/myth that has been debunked many times in print, online, and even on TV.

well....... they can debunk all they want

but if you take a 35mm SLR with a 43-50mm on it and put it up to one eye while keeping your other eye open

it will be as if there is no camera at all

this is why they refer to it as "the perspective of the human eye" (not eyeS )

and since we cant ZOOM with our eyes, but only shift focus, i dont see why any debunking needs to take place, unless its just about semantics.

our vision may be a very wide angle, but i wouldnt consider 50% of what i see usable or photography worthy, since its all blurry anyway, hell i'm typing this sentence and i can only make out 3 words to the left before it becomes illegible!
08-07-2008, 11:18 AM   #10
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so you're cheap then, not sharp in the corners?
08-07-2008, 11:18 AM   #11
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QuoteOriginally posted by Gooshin Quote
well....... they can debunk all they want

but if you take a 35mm SLR with a 43-50mm on it and put it up to one eye while keeping your other eye open

it will be as if there is no camera at all

this is why they refer to it as "the perspective of the human eye" (not eyeS )
I don't think that holds water. If that were true then when I hold my K10D with 28mm lens up to my eye and look through the viewfinder I would see the same perspective as I see if I took the camera away and looked with the same one eye.

I don't.

I see more of the scene with ONE eye than I do with a 28mm lens mounted to my K10D.

Even if i move my head (and eye) forward to where the front element of the lens was I still see a wider field of view than the 28mm lens.

There goes that theory.
08-07-2008, 11:20 AM   #12
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QuoteOriginally posted by JJJPhoto Quote
I don't think that holds water. If that were true then when I hold my K10D with 28mm lens up to my eye and look through the viewfinder I would see the same perspective as I see if I took the camera away and looked with the same one eye.

I don't.

I see more of the scene with ONE eye than I do with a 28mm lens mounted to my K10D.

Even if i move my head (and eye) forward to where the front element of the lens was I still see a wider field of view than the 28mm lens.

There goes that theory.

well, when i put a 50mm, even on my DSLR, and have both eyes open, the things in the viewfinder are the same size as in real life

when i put on a 20mm, things in the view finder are shrunk more compared to the real eye

and when i put on a 200mm, things in the view finder are magnified compared to the real eye

i just did this, cuz i happen to have all 3 here...

Last edited by Gooshin; 08-07-2008 at 11:26 AM.
08-07-2008, 11:24 AM   #13
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QuoteOriginally posted by VAV Quote
I didn't know 43mm is the diagonal of the 35mm film. But isn't 50mm usually considered to be the 'normal perspective' of our vision?
The first thing to know is that all numbers on lenses are rounded off. A Canon 50mm might in fact be a 52mm when tested. A Vivitar maximum f/2.8 might actually be f/2.9. But Pentax has this odd-ball impulse to correctly label their gear. So one lens might be released as a f/1.8 and the next f/1.9. Any other manufacturer would let the .1 slide for the sake of consistency and marketing.

Second, 50mm is not the true film normal dimension, it's just an approximation that came to be common. Pentax went back to the drawing board for the FA43. Remember it was the first of the Limited line... the photography world had seen nothing like it for SLRs. It is a completely idiosyncratic lens.

My theory with the FA31 is that they set out to design another 28mm... something conspicuously missing from the contemporary lens line-up, you'll note. But when it came out it of the lab it was a 31mm. Shaving off 3mm would have meant compromising the design. So they didn't.

Ditto the FA77, which might have been designed as a 75mm between the 50mm and 100mm. Just guessing now.
08-07-2008, 11:29 AM   #14
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QuoteOriginally posted by Gooshin Quote
remember all view finders display only a portion of the actual image (93-95%) in todays cameras, so you have to keep that in mind
Good point.

There is also a lot more to human vision that the static field of view. Our eyeballs jitter about all the time gathering in information from all over a wide angle, so our brain can assemble it into a static image that doesn't really exist.

This has many advantages including the omission of the blind spot we have due to our retina. We don't actually see a big black hole in front of us, thank goodness.

In fact, if our eye was to stay still we'd be blind, since the rods and cones only sense changes to light, not the light itself.

Humans... ain't we interesting?
08-07-2008, 11:32 AM   #15
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QuoteOriginally posted by rparmar Quote
The first thing to know is that all numbers on lenses are rounded off. A Canon 50mm might in fact be a 52mm when tested. A Vivitar maximum f/2.8 might actually be f/2.9. But Pentax has this odd-ball impulse to correctly label their gear. So one lens might be released as a f/1.8 and the next f/1.9. Any other manufacturer would let the .1 slide for the sake of consistency and marketing.

Second, 50mm is not the true film normal dimension, it's just an approximation that came to be common. Pentax went back to the drawing board for the FA43. Remember it was the first of the Limited line... the photography world had seen nothing like it for SLRs. It is a completely idiosyncratic lens.

My theory with the FA31 is that they set out to design another 28mm... something conspicuously missing from the contemporary lens line-up, you'll note. But when it came out it of the lab it was a 31mm. Shaving off 3mm would have meant compromising the design. So they didn't.

Ditto the FA77, which might have been designed as a 75mm between the 50mm and 100mm. Just guessing now.
question!

why then create a 40mm and a 70mm, such concrete, rounded numbers

throw in the mix the existence of the 85 f1.4, which in light with the 1.8, 1.9 and 1.8 of the 3 "limiteds" seems rather dubious.

pentax is a weird company :ugh:
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