this post was submitted on 22 Oct 2023
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I dont mean when for example 35mm on a crop sensor "equals" a 50mm on a full frame camera. My question is a bit weird, here we go.

So i have a 18-55mm lens (on a crop camera) and people say that 50-55mm is the focal length of the human eye. Here, my experiment comes into the play:

My camera has a 1.5x crop factor so 35mm looks like 50 mm on a full frame because of narrower field of view right? So when people say field of view of a 50mm on a full frame is the same as your eye, my first thought is 50mm on a full frame = 35mm on my camera. Then what i do is i take my camera put it on 35mm and then look at the vizor. What i expect is no zoom at all but the objects look smaller in the vizor (so fov is higher). When i put my camera at 55mm, the objects size match up with exactly what i see. But from what i learned 35mms should be like a 50mm on a full frame therefore it should match my eye.

So here comes my question:

Are the numbers of focal lengths on my lens already multiplier by 1.5x ? So do i have to subdivide the numbers to get the full frame equivalent ?

Sorry for spelling mistakes.

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[–] GrindhouseWhiskey@alien.top 1 points 1 year ago

A normal lens makes pictures with perspective that feels natural. That is most of what people mean when they talk about the human eye. On a 35mm film camera or full frame digital that would be a 50mm arguably down to a 35mm. On an APS-C thats 35-27mm, on a medium format it’s around 80mm depending on film format. Outside of that and one will often look at a picture and notice the perspective imparted by the lens’s angle of view. Smartphone cameras with wide lenses have also generally moved this preference wider angle. People have peripheral vision and are constantly looking around, so it’s not really about what you can see, but how it looks. Print size, viewing distance, and the individual shot all play into how accurate this guideline is. Keep in mind that with a good enough lens and film/sensor one could get a shot at ultra wide and crop the exact image you would get all the way to super-telephoto.

As a side note, I have an Olympus OM1 that I used to shoot sports with using a 50mm f1.8 lens. That particular combination was an exact match for my vision. I could shoot vertical images with both eyes open, tracking action with my left eye and focus and compose through the lens in perfect stereo vision with my right eye. I’ve owned dozens of other cameras and no other systems did this, but it was great.

[–] jlole@alien.top 0 points 1 year ago (2 children)

Guys im sorry for this dumb post, i somehow didnt realize that looking through the viewfinder will look exactly the same regardless of my sensor size BECAUSE İ AM LOOKİNG THROUGH THE LENS NOT THE SENSOR İ AM SO DUMB SORRY

[–] Sneezart@alien.top 1 points 1 year ago

That's not right.

Take a full frame 35mm lens and mount it in a full frame body, then mount the same lens in a cropped sensor body. The fov on the cropped sensor body will be smaller than what you see on a full frame body.

Conversely. Using Nikon lenses as an example.

If you take a DX lens (cropped sensor dedicated lens), and you mount it on a full frame body, you will see a heavy vignette around the image because the projected image doesn't cover the entire fov area of the sensor.

Note. Nikon FX bodies can detect when a DX lens is attached and it will automatically crop the image to suit the lens design, you need to disable the auto crop feature in order to be able to see the vignette.

Also the black area around the sensor will be different from lens to lens. The 35mm DX is famous for offering almost complete usable FX projection, while the 50mm will show a completely black border around the centre image.

[–] robbersdog49@alien.top 0 points 1 year ago (1 children)

The viewfinder on your camera should show you what the camera will capture, so the same lens on a crop sensor will show a small field of view in the viewfinder than it would through the viewfinder of a full frame camera.

The viewfinder are different in the same way the sensors are.

[–] tmjcw@alien.top 1 points 1 year ago

Exactly the viewfinder is not the problem.

I think it's just OPs perception of their vision, it really depends on how much of your peripheral vision you notice, and expect to be included in a "normal" fov. Also your eye constantly darts around in a scene and assembles the image as you perceive it, so it doesn't actually make much sense to compare to focal lengths of camera lenses.

Just shoot with whatever lens you like.

[–] av4rice@alien.top 0 points 1 year ago (1 children)

https://www.reddit.com/r/photography/wiki/technical#wiki_should_the_crop_factor_apply_to_lenses_made_for_crop_sensors.3F

people say that 50-55mm is the focal length of the human eye

There isn't really a good answer to that. A camera takes photos of a single moment in a rectangle with hard edges. Your eyes see in a amorphous field with higher acuity in the center that gradually drops off towards the edges, and really when perceiving a scene they move around quickly to move the center around and build up an amorphous larger image over a short period of time. That can't be directly compared with a rectangle.

A 50mm focal length on full frame is the "normal" focal length (about the corner-to-corner diagonal measurement of the rectangle, or diameter of the projected image circle) so it's more or less the agreed-upon middle ground matching your vision. But it isn't exactly what your eyes see, and really no conventional photo is.

Then what i do is i take my camera put it on 35mm and then look at the vizor. What i expect is no zoom at all but the objects look smaller in the vizor (so fov is higher)

Field of view is what you can see from the scene from edge to edge of your frame.

Magnification of the image is a different issue, and also depends on things like the optics of your viewfinder itself.

[–] jlole@alien.top 0 points 1 year ago (2 children)

Oh i get it. İm asking this question because i am looking to buy a 200mm lens but is it going to look like a full frame on a 300mm or is it going to look like a full frame on a 200mm

[–] Sneezart@alien.top 1 points 1 year ago (1 children)

A 200mm lens mounted on a 1.5 crop sensor will offer the same fov as a 300mm lens mounted on a full frame sensor.

[–] wharpudding@alien.top 1 points 1 year ago

FOV, but not range.

That can be confusing to newbies

[–] TheDamien@alien.top 1 points 1 year ago

I used to use an 18-200 on a crop sensor and I currently use a 28-300 on a full frame sensor. They're basically the same.

[–] ApatheticAbsurdist@alien.top 0 points 1 year ago (1 children)

focal length should always be focal length (unless it's labeled specifically as "equivalent focal length")

... and people say that 50-55mm is the focal length of the human eye.

nit pick here: people say a 50mm equivalent is the focal length of the human eye (and only some people... others will say 35mm... others have very different answers because the eye and brain do not perceive the world the same way a camera does... it's an age old debate and doesn't have an exact answer, I digress... I'll come back to this at the end)

So when people say field of view of a 50mm on a full frame is the same as your eye, my first thought is 50mm on a full frame = 35mm on my camera

Yes

What i expect is no zoom at all but the objects look smaller in the vizor (so fov is higher)

Your viewfinder itself has a magnification to it. Many cameras have a viewfinder with something like a 0.7x magnification, which shrinks the image to your eye. You're not going to view the image on your viewfinder you're going to view it on a monitor or as a print... keep that in mind.

Are the numbers of focal lengths on my lens already multiplier by 1.5x ? So do i have to subdivide the numbers to get the full frame equivalent ?

Nope. If you take a 35mm lens made for your APS-C or a 35mm lens made for a full frame camera and put it on your camera... they'd have pretty much the same field of view.

Now here's the other thing about field of view: Look straight in front of you. Hold your hands out to either side with your fingers stretched out and slowly swing your arms forward in an arch to move them so they're in front of you. But do so slowly while looking straight ahead and keep moving your arms forward until you just start to see your hands come into your field of view. Odds are your arms are spread very wide... you'd nee a 10mm or so on your camera to photograph that wide an angle. But (assuming you still have your eyes straight forward and don't turn to look at your hands) your fingers are going to be a blurry mush. We have very wide peripheral vision but cannot really see that sharply out that far. Keep moving your arms forward until you can start to see your fingers individually... that's going to be a lot closer to that 35 or 50mm equivalent focal length. So the question of which focal length is "normal" really can't answer the way the human eye sees, but it's more about the area we tend to focus on in our day-to-day lives...

[–] oldskoolak98@alien.top 1 points 1 year ago (1 children)

iow, normal is a natural representation of near -far objects. Our peripheral is way wide, but a spherical vs flat focal plane is a game changer. No comparison. On a flat plane, any lens that projects our field of vision in its entirety will inevitably lead to terrible near-far relationships with subjects.

Btw, I'll never fly delta if you're ever behind the sticks.

[–] ApatheticAbsurdist@alien.top 1 points 1 year ago

Near-far is perspective. That is purely controlled by distance of viewer-to-subject. Focal length (combined with sensor/frame-size) just chooses the angle of view (or “crop” if you want to think about it in how we see a wider field of view with our eyes) once you’re at that given distance/perspective.

I haven’t been at the yoke in over 20 years and that was only single engine props.