Focal length EF VS EF-S

[byjesper]

So, perhaps I'm an idiot, but I need to get this explained.

Example A: Canon EOS 6D full frame + EF 50mm
Example B: Canon EOS 90D APS-C + EF-S 50 mm

Will these two produce exactly the same picture, or not? (I'm not thinking about lens quality or megapixels in the sensor.) Example A is the "Nifty fifty" – is example B also that (in old 35 mm film terms).

[rs-eos]

Correct. That would give you the same field of view.

But as others stated earlier, focal lengths won't change and could lead to undesirable outcomes.

For example, if using around 55mm for a headshot, that will lead to facial distortions. Whereas if using something closer to 85mm, that will lead to less distortions. And when using say that 85mm with an APS-C camera, your working distance will then be further away vs an 85mm used with a full frame camera.

[ebiggs1]

Bingo, you got it.

[ebiggs1]

"For example, if using around 55mm for a headshot, that will lead to facial distortions."

Even this isn't totally correct or let's say complete. If you step back a few appropriate feet the result would be identical. Exactly the same. There is no inherent advantage given to a 85mm lens for portraits or any whatever FL. The real reason certain lenses became known as "portrait" lenses was studio size. Photographers were/are limited to where and how far they could stand from the subject. This is simply another reason I don't like putting "names" on certain focal length lenses. This lens is a wide angle, this lens is normal or this lens is a portrait lens, etc.

A 600mm super telephoto is a ultra wide angle lens if you are shooting the landscapes of the Moon. It all has to do with AOV and distance from subject.