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Are "standard" lenses really standard?


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Not specifically Alpha lenses,....but...

For a long time I've been told that 50mm (or there abouts) is the standard focal length for a full frame (or 35mm SLR) because it gives a view very close to that of the human eye.

I've just been playing with my 50mm, lining it up on my computer screen, then taking the camera away and finding that my eye sees a much wider field of view (other eye closed).

I then tried again with other lenses and find my field of view is somewhere between 15 and 24mm (probably about 20mm - but I don't have that size lens for FF).

My optician has never told me I have unusually wide vision, so how am I misinterpreting the term "Standard Lens?

This question is purely out of interest - I use 50mm when I feel it's right for the subject I am photographing.

Edited by thebeardedgroundsman
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Humans have a binocular viewing angle of about 120°, which is roughly comparable to a lens with 10mm focal length on a fullframe camera. Most of that human field of view is peripheral vision though, hardly usable for recognizing subjects. Only about the central 7° cone is usable for recognizing faces, comparable to ~250mm focal length on a fullframe camera. To say that 50mm on FF most closely resembles the human field of view is therefore indeed nonsensical. Just like people claiming the human eye can discern 300 megapixels: it's our brains incredible post-processing abilities where most of the magic happens.

As to your original question, I found an interesting read here. To quote from this source:

"... the 50-mm anecdote persists—in part because of the history of lens manufacturing, but also because it taps into the latent fears, anxieties, and imaginations that surround the use of technology for seeing. It’s comforting to believe that there is a standard view, and that photographic apparatuses can reproduce it."

Edited by Pieter
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Human eye's FOV is a lot wider than any standard lens so I don't think that's the definition of a standard lens.  I have read a bit about standard lenses and more often than not, I come away more confused.  What I did find with the standard lens (50mm) mounted on my Pentax K-5, APS-C DSLR (0.92x magnification, 100% viewfinder coverage) is that when I open my left eye to look at the subject while the right eye is glued to the viewfinder, the image more or less merge together.  A Standard lens is usually defined as between 40-60mm and I can confirm a 40mm lens does about as good as a 50mm lens.  Wide angle and telephoto lenses does not work

This doesn't work with my A7II (0.71x magnification, 100% viewfinder coverage), almost 1/3 reduction in the subject magnification is too much for the brain to compensate for the difference in size between the left and right eyes' view.  Looking at DPReview of Sony APS-C e-mount cameras, A6xxx cameras have 1.05x Viewfinder magnification with 100% viewfinder coverage.  I would like to ask the members of this forum try the experiment of looking through the viewfinder while keeping the naked eye on the subject while shooting with a 'standard' lens (35 ~ 70mm focal length lenses).

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I just tried with my a6500 and 16-55 mm zoom and sure enough, both eyes lined up perfectly right at about 50 mm focal length. Hardly scientific but this sounds like a plausible explanation.

Still, this is only relevant when looking through the viewfinder. After taking the shot you'll loose context and the relation with your actual human view: the captured image becomes just a very tight crop of that human view.

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Yep, I've just tried it and sure enough it works. And I also get the other points re: peripheral vision (that was my original thought for an explanation) and of course the captured image will be different - size of print/screen etc etc.

I like the explanation in the link Pieter posted, indicating that the perspective is similar to the human eye.

This makes sense when wide angle lenses lengthen the perspective, making the foreground, mid ground and background look further apart, and telephoto lenses making them look closer together.

 

Edited by thebeardedgroundsman
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Don't forget that all of the standardization were established in the film era when SLR's pentaprism viewfinder was the state of art.  Before this you had the view camera with the upside down, left/right reversed image then came the waist level viewfinder which did not flip the subject upside down but still reversed the image from right to left.  Sure drove me bonkers when shooting with a Kowa Six medium format camera and it's waistlevel finder - a Pentax 645 with a pentaprism finder was a huge step forward for me back then.

Anyway, standard lens and whatnot, I don't think about it much these days.  I use whatever focal length lens that I deem necessary for a particular shot.  I tend to use 50 and 85mm lenses because they are the fastest lenses that I have - mainly for isolating the subject from the background.

 

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