# Rethinking focal length conventions

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Re: 6%
1

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

jrtrent wrote:

tko wrote:

You're thinking you need a 40 mm instead of 35 mm? Of what importance is this? How did you get this conclusion? How would a 85/80 = 6% difference in FL rock your world? I don't get this at all. It would seem like you think your numbers are better since they are "more rounded off," and you want lens manufacturers to come up with new products where the focal lengths are "prettier."

You may be right about the difference between 80 and 85 mm, but apparently there's a noticeable difference around 40mm:

"40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right."

And that's from Ken Rockwell himself!

He's wrong, it's 43mm is actually the perfect focal length for full frame. It corresponds to the sensor diagonal of 43.27mm.

You are both wrong. There is no such thing as a perfect FL. It is a superstition.

If you want to play word games, then fine. Enjoy yourself.

I only used the phrase "perfect" because Rockwell used it and I was replying to his quoted comment and not that I thought the 43mm focal length to be perfect focal length under all situations and circumstances.

Referring to KR is not a particularly strong argument...

I was not referring to KR, I was responding to his quoted comment.

Maybe I should have been clearer and said that 43mm is the ideal focal length for a standard lens that renders natural perspective on a 35mm or Full Frame camera?

What is a natural perspective

Natural perspective is when near and far objects bare the same relationship in the image, as they do with the naked eye.

This is happening with every lens, every FL, as long as you are shooting from the same position.

and why is the diagonal magical? As weak as the KR argument is, this one is weaker.

It's not a question of magic, it's just that if you take the continuum of potential focal lengths, for a given sensor the focal length that matches the diagonal, is the median focal length and the transition point between wide angle and telephoto for that sensor.

Now you have to define wide angle and telephoto in mm. Next, you have to explain why the "median" happens to be the diagonal of the sensor.

For a full frame sensor, this will be approximately 43mm and on Pentax/Nikon/Fuji APSc sensor approximately 28mm.

Because...?

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Re: From Rockwell's review of the 40mm pancake

SteveinLouisville wrote:

"50mm stuck because it's much, much easier to clear the flipping mirror of an SLR with a 50mm lens, but the 40mm to 45mm range (precisely 43.27mm) is what's really normal for the 35mm full-frame."

Why?

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Re: From Rockwell's review of the 40mm pancake

SteveinLouisville's gear list:SteveinLouisville's gear list
Canon EOS RP Canon EF 17-40mm f/4.0L USM Canon EF 40mm f/2.8 STM Canon RF 35mm F1.8 IS STM Macro Canon RF 24-105mm F4L IS USM +5 more
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Re: 6%

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

jrtrent wrote:

tko wrote:

You're thinking you need a 40 mm instead of 35 mm? Of what importance is this? How did you get this conclusion? How would a 85/80 = 6% difference in FL rock your world? I don't get this at all. It would seem like you think your numbers are better since they are "more rounded off," and you want lens manufacturers to come up with new products where the focal lengths are "prettier."

You may be right about the difference between 80 and 85 mm, but apparently there's a noticeable difference around 40mm:

"40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right."

And that's from Ken Rockwell himself!

He's wrong, it's 43mm is actually the perfect focal length for full frame. It corresponds to the sensor diagonal of 43.27mm.

You are both wrong. There is no such thing as a perfect FL. It is a superstition.

If you want to play word games, then fine. Enjoy yourself.

I only used the phrase "perfect" because Rockwell used it and I was replying to his quoted comment and not that I thought the 43mm focal length to be perfect focal length under all situations and circumstances.

Referring to KR is not a particularly strong argument...

I was not referring to KR, I was responding to his quoted comment.

Maybe I should have been clearer and said that 43mm is the ideal focal length for a standard lens that renders natural perspective on a 35mm or Full Frame camera?

What is a natural perspective

Natural perspective is when near and far objects bare the same relationship in the image, as they do with the naked eye.

This is happening with every lens, every FL, as long as you are shooting from the same position.

and why is the diagonal magical? As weak as the KR argument is, this one is weaker.

It's not a question of magic, it's just that if you take the continuum of potential focal lengths, for a given sensor the focal length that matches the diagonal, is the median focal length and the transition point between wide angle and telephoto for that sensor.

Now you have to define wide angle and telephoto in mm. Next, you have to explain why the "median" happens to be the diagonal of the sensor.

No I don't, there are many references online which will confirm that the 43mm lens is the ideal standard lens for full frame but if you want to be a contrarian, it is up to you to prove why all these numerous sources are wrong and why you as an individual are right. There really is no point me trying to convince you because whatever I say, you'll just disagree, as

agreement simply isn't part of your game.

For a full frame sensor, this will be approximately 43mm and on Pentax/Nikon/Fuji APSc sensor approximately 28mm.

Because...?

No, why don't you do some work and prove me wrong instead. As for perspective, I refer you to Langford, Basic Photography 8th edition, pages 84-85. A book I've recommended in the many classes I've taught.

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Re: 6%

Gerry Winterbourne wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

jrtrent wrote:

tko wrote:

You're thinking you need a 40 mm instead of 35 mm? Of what importance is this? How did you get this conclusion? How would a 85/80 = 6% difference in FL rock your world? I don't get this at all. It would seem like you think your numbers are better since they are "more rounded off," and you want lens manufacturers to come up with new products where the focal lengths are "prettier."

You may be right about the difference between 80 and 85 mm, but apparently there's a noticeable difference around 40mm:

"40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right."

And that's from Ken Rockwell himself!

He's wrong, it's 43mm is actually the perfect focal length for full frame. It corresponds to the sensor diagonal of 43.27mm.

You are both wrong. There is no such thing as a perfect FL. It is a superstition.

If you want to play word games, then fine. Enjoy yourself.

I only used the phrase "perfect" because Rockwell used it and I was replying to his quoted comment and not that I thought the 43mm focal length to be perfect focal length under all situations and circumstances.

Maybe I should have been clearer and said that 43mm is the ideal focal length for a standard lens that renders natural perspective on a 35mm or Full Frame camera?

Well, that would have been clearer and - I think - nearer to what you meant than what you said. But it still misses the point that it's only true when the picture is viewed in a specific way.

You knew what I meant from the start, you are only looking for ways to disagree in order to feed your ego.

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Re: 6%
3

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

jrtrent wrote:

tko wrote:

You're thinking you need a 40 mm instead of 35 mm? Of what importance is this? How did you get this conclusion? How would a 85/80 = 6% difference in FL rock your world? I don't get this at all. It would seem like you think your numbers are better since they are "more rounded off," and you want lens manufacturers to come up with new products where the focal lengths are "prettier."

You may be right about the difference between 80 and 85 mm, but apparently there's a noticeable difference around 40mm:

"40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right."

And that's from Ken Rockwell himself!

He's wrong, it's 43mm is actually the perfect focal length for full frame. It corresponds to the sensor diagonal of 43.27mm.

You are both wrong. There is no such thing as a perfect FL. It is a superstition.

If you want to play word games, then fine. Enjoy yourself.

I only used the phrase "perfect" because Rockwell used it and I was replying to his quoted comment and not that I thought the 43mm focal length to be perfect focal length under all situations and circumstances.

Referring to KR is not a particularly strong argument...

I was not referring to KR, I was responding to his quoted comment.

Maybe I should have been clearer and said that 43mm is the ideal focal length for a standard lens that renders natural perspective on a 35mm or Full Frame camera?

What is a natural perspective

Natural perspective is when near and far objects bare the same relationship in the image, as they do with the naked eye.

This is happening with every lens, every FL, as long as you are shooting from the same position.

and why is the diagonal magical? As weak as the KR argument is, this one is weaker.

It's not a question of magic, it's just that if you take the continuum of potential focal lengths, for a given sensor the focal length that matches the diagonal, is the median focal length and the transition point between wide angle and telephoto for that sensor.

Now you have to define wide angle and telephoto in mm. Next, you have to explain why the "median" happens to be the diagonal of the sensor.

No I don't, there are many references online which will confirm that the 43mm lens is the ideal standard lens for full frame but if you want to be a contrarian, it is up to you to prove why all these numerous sources are wrong and why you as an individual are right. There really is no point me trying to convince you because whatever I say, you'll just disagree, as

agreement simply isn't part of your game.

I see, it is a religious belief. You have no explanation.

For a full frame sensor, this will be approximately 43mm and on Pentax/Nikon/Fuji APSc sensor approximately 28mm.

Because...?

No, why don't you do some work and prove me wrong instead. As for perspective, I refer you to Langford, Basic Photography 8th edition, pages 84-85. A book I've recommended in the many classes I've taught.

Prove wrong what? A religious belief? Make it half-rational, and I will prove it wrong.

Complain
Re: 6%

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

jrtrent wrote:

tko wrote:

You're thinking you need a 40 mm instead of 35 mm? Of what importance is this? How did you get this conclusion? How would a 85/80 = 6% difference in FL rock your world? I don't get this at all. It would seem like you think your numbers are better since they are "more rounded off," and you want lens manufacturers to come up with new products where the focal lengths are "prettier."

You may be right about the difference between 80 and 85 mm, but apparently there's a noticeable difference around 40mm:

"40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right."

And that's from Ken Rockwell himself!

He's wrong, it's 43mm is actually the perfect focal length for full frame. It corresponds to the sensor diagonal of 43.27mm.

You are both wrong. There is no such thing as a perfect FL. It is a superstition.

If you want to play word games, then fine. Enjoy yourself.

I only used the phrase "perfect" because Rockwell used it and I was replying to his quoted comment and not that I thought the 43mm focal length to be perfect focal length under all situations and circumstances.

Referring to KR is not a particularly strong argument...

I was not referring to KR, I was responding to his quoted comment.

Maybe I should have been clearer and said that 43mm is the ideal focal length for a standard lens that renders natural perspective on a 35mm or Full Frame camera?

What is a natural perspective

Natural perspective is when near and far objects bare the same relationship in the image, as they do with the naked eye.

This is happening with every lens, every FL, as long as you are shooting from the same position.

and why is the diagonal magical? As weak as the KR argument is, this one is weaker.

It's not a question of magic, it's just that if you take the continuum of potential focal lengths, for a given sensor the focal length that matches the diagonal, is the median focal length and the transition point between wide angle and telephoto for that sensor.

Now you have to define wide angle and telephoto in mm. Next, you have to explain why the "median" happens to be the diagonal of the sensor.

No I don't, there are many references online which will confirm that the 43mm lens is the ideal standard lens for full frame but if you want to be a contrarian, it is up to you to prove why all these numerous sources are wrong and why you as an individual are right. There really is no point me trying to convince you because whatever I say, you'll just disagree, as

agreement simply isn't part of your game.

I see, it is a religious belief. You have no explanation.

For a full frame sensor, this will be approximately 43mm and on Pentax/Nikon/Fuji APSc sensor approximately 28mm.

Because...?

No, why don't you do some work and prove me wrong instead. As for perspective, I refer you to Langford, Basic Photography 8th edition, pages 84-85. A book I've recommended in the many classes I've taught.

Prove wrong what? A religious belief? Make it half-rational, and I will prove it wrong.

Now you're just flaming the discussion.

Complain
Re: 6%
2

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

J A C S wrote:

Phil A Martin wrote:

jrtrent wrote:

tko wrote:

You're thinking you need a 40 mm instead of 35 mm? Of what importance is this? How did you get this conclusion? How would a 85/80 = 6% difference in FL rock your world? I don't get this at all. It would seem like you think your numbers are better since they are "more rounded off," and you want lens manufacturers to come up with new products where the focal lengths are "prettier."

You may be right about the difference between 80 and 85 mm, but apparently there's a noticeable difference around 40mm:

"40mm is the "Perfect Normal" focal length for full-frame. Unlike 50mm lenses which often are too long or 35mm lenses which are often too wide, 40mm is always just right."

And that's from Ken Rockwell himself!

He's wrong, it's 43mm is actually the perfect focal length for full frame. It corresponds to the sensor diagonal of 43.27mm.

You are both wrong. There is no such thing as a perfect FL. It is a superstition.

If you want to play word games, then fine. Enjoy yourself.

I only used the phrase "perfect" because Rockwell used it and I was replying to his quoted comment and not that I thought the 43mm focal length to be perfect focal length under all situations and circumstances.

Referring to KR is not a particularly strong argument...

I was not referring to KR, I was responding to his quoted comment.

Maybe I should have been clearer and said that 43mm is the ideal focal length for a standard lens that renders natural perspective on a 35mm or Full Frame camera?

What is a natural perspective

Natural perspective is when near and far objects bare the same relationship in the image, as they do with the naked eye.

This is happening with every lens, every FL, as long as you are shooting from the same position.

and why is the diagonal magical? As weak as the KR argument is, this one is weaker.

It's not a question of magic, it's just that if you take the continuum of potential focal lengths, for a given sensor the focal length that matches the diagonal, is the median focal length and the transition point between wide angle and telephoto for that sensor.

Now you have to define wide angle and telephoto in mm. Next, you have to explain why the "median" happens to be the diagonal of the sensor.

No I don't, there are many references online which will confirm that the 43mm lens is the ideal standard lens for full frame but if you want to be a contrarian, it is up to you to prove why all these numerous sources are wrong and why you as an individual are right. There really is no point me trying to convince you because whatever I say, you'll just disagree, as

agreement simply isn't part of your game.

I see, it is a religious belief. You have no explanation.

For a full frame sensor, this will be approximately 43mm and on Pentax/Nikon/Fuji APSc sensor approximately 28mm.

Because...?

No, why don't you do some work and prove me wrong instead. As for perspective, I refer you to Langford, Basic Photography 8th edition, pages 84-85. A book I've recommended in the many classes I've taught.

Prove wrong what? A religious belief? Make it half-rational, and I will prove it wrong.

Now you're just flaming the discussion.

I could not be more serious. I do proofs for living, BTW.

Complain
Re: 6%
3

Phil A Martin wrote:

J A C S wrote:

Now you have to define wide angle and telephoto in mm. Next, you have to explain why the "median" happens to be the diagonal of the sensor.

No I don't, there are many references online which will confirm that the 43mm lens is the ideal standard lens for full frame

There are plenty of references that say it is standard; less claim that it is ideal. None of them confirms it; the most they can do is confirm that they think so.

but if you want to be a contrarian, it is up to you to prove why all these numerous sources are wrong and why you as an individual are right.

There are plenty of sources - some referred to in this thread - saying that standard/normal is anything from 40 to 60mm FF equivalent. If you think that 43mm is somehow special in that range it's incumbent on you to explain why. It isn't JACS, or anyone else here as an individual: it's a large number of people.

People used to think - and state categorically - that the sun moved round the Earth. But simply saying so repeatedly didn't make it true any more than repeating anything makes it true.

It's very simple, really - if the diagonal really does have special virtue it must be demonstrated somewhere. If it is, show us and we'll be convinced. If it isn't, why should anyone (including you) believe it?

There really is no point me trying to convince you because whatever I say, you'll just disagree, as agreement simply isn't part of your game.

This is simply mistaken. JACS, I and many others much prefer to agree - but only with things that are correct.

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Gerry
________________________________________________________________________
I'm happy for anyone to edit any of my photos and display the results
_________________________________________________________________________
First camera 1953, first Pentax 1985, first DSLR 2006
http://www.pbase.com/gerrywinterbourne
gerry.winterbourne@ntlworld.com

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Re: 6%

Phil A Martin wrote:

As for perspective, I refer you to Langford, Basic Photography 8th edition, pages 84-85. A book I've recommended in the many classes I've taught.

Thank you for the recommendation. Libraries in my area remain closed for browsing due to covid restrictions, but you at least got me to go online for the first time and see if I could get it via "curbside pickup." Sadly, no Michael Langford books in my library system's catalog.

I have read several photography books that have sections on perspective, typically saying something like, "standard lenses . . . produce pictures in which perspective manifests itself more or less as it appears in reality to the eye . . . wide angle - space appears extended and perspective exaggerated . . . telephotography - space appears compressed." (Total Picture Control , by Andreas Feininger)

Does Langford say something similar?

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Re: Rethinking focal length conventions

mcslsk wrote:

Not sure what the point is. As a rule of thump, a prime kit should contain lenses that double the focal lenght.

I know that some photographers like that scheme, but it's just an idea for someone to consider, not a rule of thumb, Much more common would have been 28/35/85, 28/50/85 or 35/50/85, I think. I don't think I've run across many photographers that do 20/40/85 or 24/50/100.

Years ago, I had a kit w/24, 50, 100, 200, 400 and enjoyed it quite a bit, but then found it limiting and ended up with a couple zooms. Today, I shoot a mix of primes & zooms, but if I were to switch to primes, my all purpose 3-prime set would be 24, 40, 105; then for nature photography, I'd want 20 and 200/400/600. It's not about how big the gaps are; it's about what FLs I like to shoot. If 40 & 105 weren't available, I'd prefer to go to 24, 35, 135.

- Dennis
--

Gallery at http://kingofthebeasts.smugmug.com

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Re: 6%

Phil A Martin wrote:

It is the focal length of the "true" standard lens, where perspective is seen as the human eye sees it. This has been an acknowledged truth throughout the history of photography and is easily demonstrated in practice.

Every lens shows the perspective of the photographer (camera). A 43mm lens produces a print that, IF viewed from a distance equal to the diagonal of the print, offers the viewer a matching FOV - you could stand in front of the original scene, hold the print in front of the scene, and it would "fit".

You can do the same with other FLs if you vary the 1/diagonal viewing distance. So that's the magic assumption - viewing distance. How often do you view photos at 1/diagonal ?

Personally, I love 40mm equivalent. I had a Minolta HiMatic with a 40/1.8. I used a 28 on APS-C for years until I switched to Nikon and haven't been excited about any of the options, so I'm living with a 35 (52mm equivalent) which I find much less useful. I think it has a pleasing, natural look, even when you don't view images at 1/diagonal, but the "matching perspective" aspect of it is mostly a mathematical curiosity.

- Dennis
--

Gallery at http://kingofthebeasts.smugmug.com

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Re: 6%

Paul Pasco wrote:

My observation going back to the 70’s was that when you put a 50mm or so lens on a DSLR and looked through viewfinder with both eyes open, the size of objects appeared very close to the same

That's going to depend on the viewfinder magnification.

- Dennis
--
Gallery at http://kingofthebeasts.smugmug.com

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