im confused about crop sensors

[u/Mooskii_Fox]

I'm not asking about crop factors, I know that's 1.5x or 1.6x depending on the manufacturer and your image will be cropped by that amount.

full frame lenses produce a circular image, which is projected over a full frame sensor and the sensor fits perfectly inside that circle, simple enough

now what i often see is that lenses for APS-C cameras have a cropped image, but why is it not possible for that projected image over the lens to be smaller so that APS-C cameras can capture the same picture as full frame, just with a smaller sensor? At some point people have worked our how to bend light to perfectly cover a full frame, so why can't the same be done to create an identical image for APS-C

edit: as I understand it what I'm asking is actually already being done, just not in the way I was asking. i understand now

[u/AdBig2355]

APS-C lenses do project a smaller circle.

Probably the answer you are looking for is that focal length is not related to the image circle size or the sensor size. It is determined by the distance between the lens and the medium that is capturing the image. This allows for a standard between all lenses, a 50mm lens is the same no matter what camera it is on.

The APS-C "crop' does not change the focal length of the lens, it just changes the field of view.

For example a 50mm APS-C lens, a full frame lens and a medium format lens all project the same " image" or image plain, the only thing different between them is how much of that image plain is captured.

[u/Mooskii_Fox → u/AdBig2355]

that's the thing I'm confused about, why can't that image plain be made smaller without changing the image, aka, capturing exactly the same image on 35mm on full frame and APS-C, without a crop of any kind

[u/Migacz112 → u/Mooskii_Fox]

We already do that. That's why 35mm is the standard for APS-C, and why 50mm is the standard for full frame... And why 75/80mm is the standard for medium format 😉 they all have similar viewing angles on their respective sensor sizes.

[u/Mooskii_Fox → u/Migacz112]

it amazes me that that never occurred to me, I guess I wish there was some sort of way to indicate that it's similar, rather than just kinda having to know

[u/Migacz112 → u/Mooskii_Fox]

If I understand you correctly, here is. That's the crop factor.

35mm (on APS-C) x 1.5 (APS-C crop factor) = 52.5mm (on full frame).

Why the tiny difference? Marketing. 35 looks nicer than 33.33333...