What is a Normal lens?

[walter23]

It just happens to be a focal length that represents the world with a comfortable amount of perspective, similar to what you'd be normally processing with your eye + brain.

Sure, you can look deep into the distance with your naked eye and see a telephoto perspective on something, or pay attention to your peripheral vision and notice a wide angle effect on your world, but most of the time you're probably scanning and attending to the world from a roughly normal perspective.

Just happens that a film diagonal focal length roughly matches that, I guess.

BTW reading over the first bit of the thread I guess my first response was a bit repetitive. Sorry for that.

and what makes the format diagonal so special, so normal?

most 50mm SLR lenses are double gauss designs which are retrofocus.

 

[cotdt]

But but... your human eyes are ultra wide angle lenses, much wider than 50mm for 35mm.

 

[JBrunner]

But but... your human eyes are ultra wide angle lenses, much wider than 50mm for 35mm.

Yes, but your attention is focused on a much narrower field of view. Your peripheral vision exists only to attract the attention of your forward looking perception. We have the eyes and perception set up of a carnivorous predator, not a herbivore.

 

[Michel Hardy-Vallée]

the retrofocus 35mm Distagon actually outperforms the 35mm Biogon, it's just such an amazing lens. maybe retofocus is not so bad after all.

Totally possible. Again, the essential difference between retrofocus and non-retrofocus design is how far from the film can you put a lens. If someone manages to make a better lens one way or another, I'm not arguing. However, I've seen a lot of rave reviews about the Biogon, but not much about the Distagon, so I don't know more than that.

 

[John Koehrer]

The original Barnack design camera used a 50mm lens designed for 18X24 & he had a lens made in the same fl with enough coverage for what we now know as "full frame"
The fl just became a convention & isn't worth worrying about.