normal lenses

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RalphLambrecht

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a 'normal focal lengthlens is typically defined as havinga focal length equal to the film-format diagonal. in case of 35mm film that is close to 43mm. so, why, I ask don't we see lenses with that focal length?; we have many close to it; 35 or 50mm,but I've never seen 43 or ;let's say 45mm.why do you think that is?I use 35 and 50mm a lot and can see 43 or 45 having an advantagein viewing angle and weight over the typical 500mm normal.:whistling:confused:
 

E. von Hoegh

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I'm willing to bet it has something to do with that mirror... most 'normal' 50s are retrofocus, to give room for a decent size mirror. The flange to filmplane distance on most slrs is around 45mm.
Quite a lot of 35mm fixed lens rangefinders came with ~45mmlenses, which reminds me that Leica seemed to settle very early on a 50 as their standard - so for that matter did Zeiss with the Contax, although there was no mirror to give room to.
 

miha

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Most probably because Leica was launched with that focal length and people got use to it.
 

MDR

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Plenty of 45mm lenses the Nikon GN Pancake is a 45mm, Pentax made a 43mm lens, Minota MD 45mm, etc.... The lenses for the early Contaflexes were 45mm as well, the standard lens for Contax G was a 45mm Planar. Some fixed lens RF cameras of the 50 to 80's had 45mm lenses. It's interesting to note that many 45mm lenses were Budget lenses and/or Tessar Design. I believe the reason that so few people use these focal lenght has to do with the fact that it's neither wide angle nor tele it's an in-between focal lenght in 35mm. In MF the vast majority of early 6x6 was fitted with what would amount to a 45mm lens the 75mm lens.
I personaly love 45mm lenses because they are just a little wider than 50mm but still offer the advantages of the longer focal length in terms of speed and look.
 

Sirius Glass

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As noted in Post #2, the retrofocus needs of 35mm slrs was a major force to push 50mm lenses to become a defacto normal standard 35mm lens.
 

gleaf

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Normal essentially is what you normally see when you look. Or near when focal length equals the diagonal of the selected image size.
 

Peltigera

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A quick look at my 35mm cameras shows me:

Olympus Trip 40mm
Zeiss Ikon Contina Ic and IIa both 45mm
Agfa Sillette 45mm
Paxette I and II both 45mm
Balda Baldessa 45mm
Minolta Uniomat 45mm
Halina 35X 45mm
Yamato Pal Jr 45mm

That is about half of my 35mm cameras - not rare if 50% of an essentially random selection have 45mm lenses.

I think it needs saying that the diagonal of the image as focal length is a very rule of thumb quantity - there is no biological or mathematical reason for it, it is just a relationship that has been noted to produce a similar flat image as the human eye does on a doubly curved image sensor.
 
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cliveh

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a 'normal focal lengthlens is typically defined as havinga focal length equal to the film-format diagonal. in case of 35mm film that is close to 43mm. so, why, I ask don't we see lenses with that focal length?; we have many close to it; 35 or 50mm,but I've never seen 43 or ;let's say 45mm.why do you think that is?I use 35 and 50mm a lot and can see 43 or 45 having an advantagein viewing angle and weight over the typical 500mm normal.:whistling:confused:

Rather than express normal in terms of format diagonal, would it not be better to express it as cropped fine definition within peripheral vision? And would that not mean 50mm on a 35mm camera would fit the bill?
 

Pioneer

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As has been said, lots of them out there. Here is only a few I own, or have owned.

Minolta MD 45 (A stunning and very under-rated lens)
45mm Tessar on the Contaflex
Pentax FA43mm Limited
Pentax M 40 (I once toyed with gluing this one to one of my LX's)
Pentax DA 40 Limited (Hands down the best normal lens I have ever owned, and I have owned a lot of them.)
75mm Tessar on Rolleiflex Automat
75mm Solinar on Agfa Super Isolette
Pentax SMC FA and A 75mm for 645 (Another truly stunning and somewhat under rated lens)

I love them every one. :smile:
 

Dan Fromm

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I'm willing to bet it has something to do with that mirror... most 'normal' 50s are retrofocus, to give room for a decent size mirror. The flange to filmplane distance on most slrs is around 45mm.
Quite a lot of 35mm fixed lens rangefinders came with ~45mmlenses, which reminds me that Leica seemed to settle very early on a 50 as their standard - so for that matter did Zeiss with the Contax, although there was no mirror to give room to.

Emil, as has already been pointed out, Leica started it. Zeiss-Ikon and Nagel copied Leica. That historical accident is the reason 35 mm cameras with 24 x 36 gates have 50 mm (or so) lenses as standard, but no one's explained the historical accident.

The Leica was initially conceived as an exposure test device for 35 mm cinema. The 35 mm cine camera's gate is 24 x 18 mm. That's the so-called Edison format and yes, T. A. Edison invented it. By convention -- set to gain working distance -- the "normal" focal length for 35 mm movies is ~ 50 mm. That's what Oscar Barnack used on his exposure tester. When the exposure tester grew into a camera that should double frame 35 mm (24 x 36) the 50 mm lens was retained.
 

Gerald C Koch

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Pentax makes a 43 mm normal lens.

Lens design involves a lot of compromises. It may be simpler to design as lens with a slightly longer focal length.
 

Hatchetman

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check out this little banty

44mm Ektar
 

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Loren Sattler

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I believe that defining normal focal length as the length of the diagonal of the film format may be an error. It should be a function of the width of the film format rather than the diagonal because that is what your peripheral vision sees.

I hope this explains my thinking. The "normal" lens for 2-1/4 sq calculates to 80.8mm. The ratio between 2-1/4 in and 80.8 is 1.414. If you apply this ratio to the width of the 35mm format (36mm width x 1.414), this calculates to approx 51mm.

This implies that the "angle of view" of a 50mm lens with 35mm format would be similar to an 80mm lens with 2-1/4 in format. These focal lengths are what many manufacturers consider normal for these formats.

I learned this while working with a Widelux which uses 35mm film. The film format is so wide that the film acts more like medium format than 35mm film when enlarging, i.e., you need a longer enlarger lens and the grain and quality is more like medium format.
 

darinwc

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a 'normal focal lengthlens is typically defined as havinga focal length equal to the film-format diagonal. in case of 35mm film that is close to 43mm. so, why, I ask don't we see lenses with that focal length?; we have many close to it; 35 or 50mm,but I've never seen 43 or ;let's say 45mm.why do you think that is?I use 35 and 50mm a lot and can see 43 or 45 having an advantagein viewing angle and weight over the typical 500mm normal.:whistling:confused:

re: "43 or 45 having an advantage in viewing angle and weight over the typical 50mm normal"

Actually, a 43mm or 45mm lens may end up being larger and heavier than a comparative aperture 50mm. In order to have a lens which corrects for the aberrations of a wide aperture AND be retro-focus, more elements would be needed and possiblly larger front elements.
Just look at the size and complexity of wide-angle SLR lenses compares to rangefinder wides. The SLR wides are generally much larger and heavier because they have to be retro-focus. The same would probably be true for 43mm lenses faster than f2.

Note that the 45mm 'pancake' lenses for SLR's are usually 4-element slower lenses. None are f1.4.
 

blockend

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The Canon 40mm 2.8 is an excellent compact lens and can be used on EOS SLRs. In recent times I've returned to 50mm lenses after a long period shooting 28mm, but the 40mm seems more natural than either.
 

Sirius Glass

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Voightlander Vito II 50mm lens and it is a folder.
 

pen s

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I've had a couple of those 40mm f2 Zuikos but they were too valueable to keep so I sold them to finance other lenses. I am used to the 50mm and like it's angle of view. No other reason than that.
 

AgX

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There are at least three ways to estimate a "standard" focal lenght, with different results.
 

baachitraka

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...and they are?
 

AgX

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Definitions:

Standard Focal Length =

1) lenght of format diagonal

2) arithmetical mean of 1.5x image height and 2x image width

Both definitions rely on a image presented at maximum size at short viewing distance (30cm).


3) a compensated form of 2) with a lengthening factor if the visual image is small (as often in cinema or at watching TV)
 
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