Picture Taker Loc: Michigan Thumb

Telephoto lenses compress the picture and Wide angle will spread them out. This is way of cameras and the lenses. By the way the 50mm rile is assuming the 50mm lens is on full frame camera. On a Canon non full frame its 31.25mm or Nikon a 33.3mm.

fosis Loc: Pittsburgh, PA

JD750 has the right idea. (May 30, 2020 13:14:22)
"Normal" has been calculated/defined as the focal length that has a field of view that's equal, out in front of the camera and back to the film plane. The diagonal for a full frame (24 x 36mm) equals the square root of (24 squared + 36 squared), which equals 43.26mm. So that focal length will provide a field of view out in front of the camera that will equally cover the field of display at the film plane.
JD750 says "field of view" is what's important. That's because we see the magnified effect of a wide angle lens simply by how we view an image that was taken with it. It will look normal if we hold a print close to us. It will look "wide angle" if we hold the print farther away from us, because the perspective in the image won't change, but the perspective that we see it as a print is different than that. Similarly, a telephoto picture will look "telephoto" if we hold the image close to us. That's why telephoto sunsets seem to have inordinately large suns.
That's the "magic" of using varied focal length lenses. We do this all the time to make a photo more dramatic. The perspective doesn't change as the picture is taken, only the field of view. But when we show a completed image afterwards, the telephoto's compression of its perspective, or the wide angle's seeming exaggeration of large foreground/small background becomes apparent. Just hold a wide angle shot way out in front of you. You'll see why it's the field of view at the time of seeing the final image, where the perspective actually seems to change.

TomHackett Loc: Kingston, New York

Fosis makes an important point about "compression." If you take an image with a 400mm lens and, standing at the exact same spot, take a second image with a 50mm lens, the apparent "compression" will be the same with both. In other words, if you crop the image taken with the 50mm lens to the dimensions of the image taken with the 400mm lens, the compression, that is, the relative distance between nearer and farther objects, will be identical. In fact, except for the loss of quality from the cropping (and any variations in quality of the lenses), the images will be identical.

For a long time, I have wished that instructors would give more emphasis to the perspective, or the location of the photographer, than to the focal length of the lens, when talking about compression and apparent elongation.

So when the OP said, "I noticed that the compression was considerably more when viewed through my 8x 42 binoculars." I have to ask whether he is talking about viewing the scene from the same spot. If so, I don't quite understand what he means by "compression."

John N Loc: HP14 3QF Stokenchurch, UK

On the same point, maybe a yard or so as I put the camera down and picked up the binoculars. The scene I was looking at was the M40 motorway snaking out over the Oxfordshire Plain to Birmingham, viewed from the Chilterns at least a couple of hundred feet higher. I was using the 400mm to try and 'compress' distance from back to front of the image to exaggerate the bends in the road. I couldn't get exactly what I wanted as a new fence has been put in place since I first saw this scene.

So I got out the binoculars to view the red Kites wheeling around the sky doing their aerobatics and looked at the motorway again. And the view appeared to be tighter, i.e. more compression. Hence my question on the focal length of the eye (may have been wrongly titled) because I assumed a 400mm lens would be 8x a normal view but my 8x binoculars gave a different view, sufficient for me to query.

If I get the chance tomorrow I'll go back and snap it, it might add something to just imagination. I might also try using my 24-105 @ 50mm because I'm not understanding your view on cropping.

chrisg-optical Loc: New York, NY

Some time ago I read that the human eye is closest to about a 42mm FF/35mm frame equivalent. Telephoto lenses compress perspective, and binoculars probably more so with the smaller "eye sensor".

wdross Loc: Castle Rock, Colorado

The eye is one of the most fascinating objects known to mankind. It can only see fine detail for 3.5° to 3.8° and detail up to ~5°. Because of the eyes quick focusing and processing, "detail" vision amounts to about 10° and "normal" vision amounts to about 50°. Peripheral vision is ~180° and the ability to perceive light extends to about 220° (there is a translucent area to the eye where the cornea, lens, and iris attaches to the rest of the eye). Color is best perceived in the 5° (the fovea) since they are all cones. Outside the fovea area, the rods and cones start at about 50%/50% with the cones decreasing as one get further away from the fovea. The rods are basically black and white receptors. As mentioned, the eye varies greatly as to what it's "actual" focal length is. And there are still more things like vision purple and a vision "dead" spot in the eye. "Relative" focal length: 20 to 24.

larryepage Loc: North Texas area

In my experience, the idea of a "normal" lens has much more to do with the foreshortening that a telephoto lens creates and the stretching that a wide angle introduces in the relative distances of objects at various distances in an image. This is relatively regardless of image cropping, regardless of presentation medium and regardless of print size, and really mostly in spite of viewing distance. Viewing angle changes with any or all of those variables when creating a physical image. And for that reason, moving closer or farther away from a subject is not exactly the same as changing lens focal lengths, because the representation of the ratios of distances is not the same. You can demonstrate this for yourself simply by sketching a scenario and altering framing by moving around vs. by changing lenses. This is why "zooming with our feet" sometimes works and sometimes doesn't, just like moving closer sometimes produces preferable results to zooming your lens.

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Verrrrrrrrrrrry crudely it’s about an inch. But the FL hardly tells you what you see. It can be rather misleading to compare the eye to a camera.

Surely somewhere sometime you’ve seen a life size model or a real human eye ? Or maybe you have a rough idea of the size from the eye socket in a skull. Given the approximate wall thickness it looks like the lens to receptor distance ought to be about an inch.

The receptor is concave so an exact FL is prolly not available. Recall how two 16mm FL lenses can have very different views, one is fisheye and the other is rectilinear ?

Okay so all the above is about actual FL of the lens, very approximately an inch. Now consider that the eye operates as a swing lens pano camera ! All in all there’s no single answer when trying to compare the eye to a mini camera of typical design.

John N Loc: HP14 3QF Stokenchurch, UK

Here is the scene in question. It shows the curvature in the road and illustrates what I mean my compression.

I went back this morning to check and my binoculars (8x) seem to 'compress' the image more than the 400mm lens. But I'm beginning to see why - manufacturing tolerances on a lens are a lot tighter than variables in the eye.

I tried to check mine this morning using my 24-105mm stm lens as per JD750's suggestion. I sat on one spot with the camera in front of me and I seemed to have a wider F.O.V. than the lens at 24mm. But this test is compromised because I sat in an area I knew well - and I'm sure the brain was filling in for what I knew was at the periphery. I could also detect a raised finger on an oustretched arm at close to 90° each side.

Thanks for all the replies, I think I've learned something but I'm not quite sure what! I really need to put the camera on a spotting scope and compare that with what my eye sees. Maybe after Christmas.

M40 (from Chilterns viewpoint)

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Must be something wrong with your gear cuz it makes it appear that everyone is driving on the wrong side of the road.

jwreed50 Loc: Manassas, VA

This has been a matter of long-standing controversy among Leica users. Some Leica users say that the 50mm lens is the "normal" lens for 35mm cameras -- others say that it is the 35mm lens. I tend to agree with those who say the 50mm, which is why that lens is the default lens on my M10.

Ultimately, it's a question human perception and there no doubt is a lot of variation in the "normal" FOV among different people. The best answer is to have both a 35mm and a 50mm lens -- that way you're covered either way!

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We used to explain to customers who referred to the “field of vision” this way:

Whole vision incl extremes 16-20mm.
General area, non attentive 28-35mm.
Attentive to some thing 85-135.

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You’ll notice 24 and 50 are missing. Those two are not great matches for the three categories. What makes them both so very popular is that they are very handy compromises between categories. 24 can somewhat manage the “Whole” and the “General”, while 50 can handle some of “General” and most of “Attentive”.

So with 24 and 50, a bit of compromise or a bit of cropping lets that pair cover the waterfront. The old Leica pair was 35 and 90, mostly due to the nature of Leica’s hardware at the time but equally as handy as the modern 24 & 50 kit.

jwreed50 Loc: Manassas, VA

I agree that if you're looking for the best 2 lens combo on a Leica M, it's the 35-90 combo. For a 3 lens combo, I'd go with 24, 50, and 90.

n3eg Loc: West coast USA

I go by this: Both eyes = 35mm FF FOV, one eye = 50mm FF FOV.

My field of concentration, though, is more telephoto.

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Great triple combo. For Leica-style stuff I use the exact equivalent on a Pen-F, fast and tidy little 12, 25, and 45 Zuikos. This kit not only serves very well for Leica-like working, it also really looks the part ... all retro chrome and such. Only thing missing is the Leica price but I’m OK with that one minor flaw. I’ll get over it, somehow.