Rethinking focal length conventions

Started 7 months ago | Discussions thread
Phil A Martin
Phil A Martin Veteran Member • Posts: 6,407
Re: 6%

Paul Pasco wrote:

Phil A Martin wrote:

Gerry Winterbourne 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.

There is no single "perfect" focal length. Human eyes vary in size; if "perfection" means matching human vision then it varies depending on the individual. 43mm was picked out of the range of visually "normal" focal lengths because it corresponds to the diagonal of 135 format - an arbitrary choice that doesn't confer perfection.

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.

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

And this is the important point, not the angle of view. With a 43mm lens, the sizes would appear even closer.

but that totally discounts how much the eye takes in from the periphery that is cut off by the viewfinder boundaries. So, the eye actually has a much wider field of view than that of a 50mm lens in a FF camera. The eye/brain “system” is based on a sphere and behaves very differently than a lens and a flat focal plane.

I'm not saying this is wrong but I don't see it's relevance? What we are doing when we are taking photographs, is framing small sections of what we see in front of us and turning it into 2D images.

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

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Regards, Paul
Lili's Dad
WSSA Member #450

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