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A place to politely discuss the tools, technique and culture of photography.

This is not a good place to simply share cool photos/videos or promote your own work and projects, but rather a place to discuss photography as an art and post things that would be of interest to other photographers.

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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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[–] 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.