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Are focal lengths on crop sensor lenses same as full frames ? (alien.top)

submitted 1 year ago by jlole@alien.top to c/photography@viewfinder.pro

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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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[–] 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

[–] 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.

[–] 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