[Blue]

To get this back on track to the OP and title. The designer explains why the focal length of the FA 43 and 77 Ltd lenses were chosen in this article. These were scanned by VOE and this is his flickr stream.

[builttospill]

Interesting the LX pictured with the 77 is not black. I can't see the LX 2000 stamp on it either. But then I'm sure famous lens designers get to use cameras we don't always get to see.

[clutch]

The comes up from time to time but the M 40 (released in 1975) only shares the optical layout 5/4 with the DA 40 ltd.

My mistake, Blue. Thanks for the clarification. I had assumed the DA40 descended from the M40 just based on the outward appearance. My original point was actually that a pancake 40mm lens wasn't a new concept for Pentax, since the M40 has been around for over 35 years.

[Ben_Edict]

Nope it actually just is coincidence it's the diameter of the sensor/film so that's not the reason.

Wiki has it written down quite well.

In photography and cinematography a normal lens is a lens that reproduces a field of view that generally looks "natural" to a human observer under normal viewing conditions.

For still photography, a lens with a focal length about equal to the diagonal size of the film or sensor format is considered to be a normal lens; its angle of view is similar to the angle subtended by a large-enough print viewed at a typical viewing distance equal to the print diagonal; this angle of view is about 53° diagonally. For cinematography, where the image is normally viewed at a greater distance, a lens with a focal length of roughly double the film or sensor diagonal is considered 'normal'.

Whatever "Wiki" you refer to, this is not the standard source of wisdom. It is where everybody can pollute the web with his personal knowledge or half-knowledge.

I quote from the Focal Press Encyclopedia of Photography: "Normal Lens. Defined for photography as one whose focal length is equal to the diagonal length of the film format in use..."

I think, this definition has been around for the last 100 years, whatever Wiki-something writes.

Pentax choose the 43mm fl quite deliberately and you may research interviews with Pentax officials over the last two decades, who always underline exactly this point.

Ben

[Blue]

My mistake, Blue. Thanks for the clarification. I had assumed the DA40 descended from the M40 just based on the outward appearance. My original point was actually that a pancake 40mm lens wasn't a new concept for Pentax, since the M40 has been around for over 35 years.

Clutch, I suspect that the M 40/2.8 was the inspiration and starting point for the DA 40/2.8 Limited given their 5/4 arrangement. They are also laid out the same way but with redesigned elements. When I first saw the DA 40, I made the same assumption. It is amazing that the M has been around since 1975.

[Anvh]

Whatever "Wiki" you refer to, this is not the standard source of wisdom. It is where everybody can pollute the web with his personal knowledge or half-knowledge.

I quote from the Focal Press Encyclopedia of Photography: "Normal Lens. Defined for photography as one whose focal length is equal to the diagonal length of the film format in use..."

I think, this definition has been around for the last 100 years, whatever Wiki-something writes.

Pentax choose the 43mm fl quite deliberately and you may research interviews with Pentax officials over the last two decades, who always underline exactly this point.

Ben

I think you're mission the point amd im not saying you're actually wrong but just that it happened to be the case it works like that, let me get to you via a different way.

Can you explain to me why a lens that has a diagonal length of the film is called a "normal" lens?


Kodak
Normal Lens
A lens that makes the image in a photograph appear in perspective similar to that of the original scene.

[Sandy Hancock]

Anvh (and Kodak) are right. The definition of a normal lens is one with a similar depth perspective to the human eye. That is why it is called "normal".

It just so happens that the focal length which produces this effect for a particular system is approximately equal to the diagonal dimension of the frame. That is an interesting reality of optical physics, but it not a definition.

[Blue]

Anvh (and Kodak) are right. The definition of a normal lens is one with a similar depth perspective to the human eye. That is why it is called "normal".

It just so happens that the focal length which produces this effect for a particular system is approximately equal to the diagonal dimension of the frame. That is an interesting reality of optical physics, but it not a definition.

Sometimes there is more than 1 definition for a word or term. I have seen sources that used either and a few that used both. There is variability from one person's eye to the other. However, that doesn't really matter. In the context of this thread, the FA 43/1.9 Ltd was designed due to the diagonal of the 135 system being ~ 43mm as per the designer's article above. In fact, the designer of the 43 used the diagonal as the definition on page 78 of the above article.

[lytrytyr]

The Kodak definition is not precise, since the framing of "the original scene" isn't specified.
If I look with tunnel vision, I'll see a scene that would be Kodak-normal for a telephoto.
If I take in a broad scene by scanning my eyes, the scene would be Kodak-normal for a wide-angle.
It's all too vague for a good definition.

The Focal Press definition is exact: the diagonal of the film format.
If it happens to give the same number
as someone's interpretation of the Kodak definition,
then so much the better for the Focal Press definition.

[paperbag846]

If I take in a broad scene by scanning my eyes, the scene would be Kodak-normal for a wide-angle.

The right thing to consider is not field of view but perspective. 43/50mm lenses give the same perspective our eyes see (assuming you are using a full frame camera... it should be approximately 28-35mm for a crop sensor). Wide angles exaggerate the distance between near and far objects, while telephoto lenses compress those differences. A 21mm lens gives me approximately the same FOV as what my eyes see, but it also distorts perspective in a way that looks really cool, but not "normal".

[Anvh]

Sometimes there is more than 1 definition for a word or term. I have seen sources that used either and a few that used both. There is variability from one person's eye to the other. However, that doesn't really matter. In the context of this thread, the FA 43/1.9 Ltd was designed due to the diagonal of the 135 system being ~ 43mm as per the designer's article above. In fact, the designer of the 43 used the diagonal as the definition on page 78 of the above article.

Sure then answer me this.

Why is it called a normal lens?
The word normal certainly stands for something or else it wouldn't be there so do your best to explain it.

Besides it's not a definition but more a "rule" then something else since it's use to get you the normal focal length number but it doesn't explain to you why it's considered normal. Two very different things.

[Anvh]

The Kodak definition is not precise, since the framing of "the original scene" isn't specified.
If I look with tunnel vision, I'll see a scene that would be Kodak-normal for a telephoto.
If I take in a broad scene by scanning my eyes, the scene would be Kodak-normal for a wide-angle.
It's all too vague for a good definition.

The Focal Press definition is exact: the diagonal of the film format.
If it happens to give the same number
as someone's interpretation of the Kodak definition,
then so much the better for the Focal Press definition.

Actually you're perfectly correct with the first part and so that's why we look at the final image (printed), wiki explain it better.

For still photography, a lens with a focal length about equal to the diagonal size of the film or sensor format is considered to be a normal lens; its angle of view is similar to the angle subtended by a large-enough print viewed at a typical viewing distance equal to the print diagonal; this angle of view is about 53° diagonally. For cinematography, where the image is normally viewed at a greater distance, a lens with a focal length of roughly double the film or sensor diagonal is considered 'normal'.

The right thing to consider is not field of view but perspective. 43/50mm lenses give the same perspective our eyes see (assuming you are using a full frame camera... it should be approximately 28-35mm for a crop sensor). Wide angles exaggerate the distance between near and far objects, while telephoto lenses compress those differences. A 21mm lens gives me approximately the same FOV as what my eyes see, but it also distorts perspective in a way that looks really cool, but not "normal".

Right on the money =]

[Blue]

If you look at my post, you will see that I said words and terms sometimes have more than 1 definition and I have seen valid sources with either and some with both. I gave you an example of the diagonal as the definition from the designer of the 43mm lens. However, you are much smarter than the engineer that designed several of the LTD lenses an others. That said, the normal lens is based on the human perspective. However, that varies from person to person, hence there have been normal lenses designed for 135 platforms ranging from 40mm to 58mm due to that variability. The best way to come up with a mathematical definition is to measure the diagonal of the film or sensor. In the case of 135, it is ~ 43mm. But due to variation in the human population, that can be different for each person. Since 1952, Pentax (Asahi Optical) has built normal lenses for 135 in 40mm, 43mm, 50mm, 55mm and 58mm. Asahi also used the term "standard" lenses in the past. If you look in the glossary of John Hedgecoe's book The New Manual of Photography (2003) the definition of a "normal lens" is a standard lens. His definition of a standard lens is:

Focal length of the lens is roughly equal to to the diagonal of the image area. For the 35mm format, the standard lens is normally considered to be the 50mm. The lens approximates to the central, nonperiphery angle of view of our eyes.

This last part is where the variation of the human eye comes in from person to person. It even may vary during the life of a person,

I give as references Hirakawa Jun (page 98 in above article posted) and John Hedgecoe's book. In addition to the glossary, Hedgecoe discusses the standard lens on page 40 of the above book.

[Anvh]

Blue you cant read can't you?
I said i wouldn't call it a definition because it doesn't explain anything, it's just a formula or a rule not an explanation, meaning or reason.
If our vision was different then we wouldn't call the diagonal of the sensor a normal lens would we?


Besides that definition you quote is bullocks, the fevoa only sees 2 degrees and that's the central part of our vision that isn't considered peripheral.

And as reference i give you this book www.cis.rit.edu/fairchild/CAM.html
But really though, you can verify this with most books about the human eye.

Even if the number was correct it still is incomplete because what do we use as the source image, that what we see in the viewfinder, on the monitor, printed?

[Blue]

Blue you cant read can't you?
I said i wouldn't call it a definition because it doesn't explain anything, it's just a formula or a rule not an explanation, meaning or reason.


Besides that definition you quote is bullocks, the fevoa only sees 2 degrees and that's the central part of our vision that isn't considered peripheral.

And as reference i give you this book www.cis.rit.edu/fairchild/CAM.html

Apparently you are the one that can't read. That is why you have been on my ignore list because you ultimately stoop to personal attacks. There is an article posted here that is by the engineer that designed the 43 and I gave you a book by Hedgecoe (2003). Try reading those. The are considered "peer reviewed" publications.

Here is something else for you to practice your reading skills on:

http://www.photographymad.com/pages/view/standard-lenses

As far as biology stuff goes,the foveal region is surrounded by the parafoveal region while the 1 to 2 degrees of the foveal region is the sharpest. However, the parafoveal can go up to 30 degrees into the near periphery. It is about the perspective created. If you look, you will see that Hedgecoe said eyes and not eye. However, this is the reason a numerical definition or rule was adopted by some to describe a normal or standard lens. The point is that a standard lens will give closer to a natural view of a subject than wide angles or telephoto lenses. However, the foveal stuff you dragged into the discussion and has nothing to do with the Hedgecoe qoute.