Thank you everyone for your great responses. It's definitely helping me wrap my head around these things as as newcomer.
Just to be idiot-proof on my end: if I buy a 16mm APS-C lens (like the one linked below), slap it on my A6000 APS-C camera and take a picture, the focal length will be
________?
24mm?
https://www.bhphotovideo.com/c/product/1369132-REG/sigma_402965_16mm_f_1_4_dc_dn.html
The focal length will look the same as a 24mm does on a full frame camera (same angle of view). It’s still a 16mm lens, but on a crop sensor it will “look like” a 24mm lens due to the crop factor (because lenses are listed at a 35mm equivalent focal length, regardless of sensor size). Another example is in the m43 system, it’s a 2x crop factor. So you will see ultra wide focal lengths that aren’t so wide when you’re put it on the camera. A 9-18mm lens in the micro four thirds mount would “look like”, or be equivalent to, an 18-36mm lens on a full frame (35mm) sensor.
Gotcha. As another poster mentioned as well, I think I'm confusing focal length with field of view. So, if I take a 16mm focal length lens designed for APS-C, and put it on my APS-C camera, I will get a
24mm field of view on my APS-C camera pictures?
I think I was using the wrong wording as well. I understand that I'm never changing the inherent physical focal length of a lens by putting it on an APS-C vs full frame camera, but I am changing the field of view.
Same goes for the opposite direction correct? When I take a 35mm *full frame* lens and put it on my APS-C camera, the field of view changes to roughly 50mm since I've cropped the larger (full frame/35mm) field of view down with my APS-C camera sensor.
You’re starting to get it.
But there’s no such thing as a “
24mm field of view.”
This confuses me a bit- if we scrap my question about APS-C completely, and put a normal full frame 24mm lens on a full frame camera and took a picture, then what would the field of view be for that picture? I would
not call that a 24mm field of view?
The point I'm making is that describing a focal-length FOV without specifying the size of the sensor or film behind it perpetuates confusion and misunderstanding.
"24mm field of view." = nonsense. No such thing.
"24mm field of view on fullframe." = everyone gets that, it's clear, and doesn't perpetuate misunderstandings.
"24mm full-frame equivalent." is slightly more concise and everyone gets that too.
To my limited knowledge, a focal length has a number of inherent properties: for instance a wide angle lens will have more distortion (stretch certain areas), and less compression, making distant objects seem further away. Would it be accurate to say that a "24mm focal length" encompasses these properties? Instead of a 24mm "field of view"?
No. There's nothing about the focal length that has those properties. It's
always about the
combination of focal length & sensor/film size.
Example:
You might think 100mm is "inherently" telephoto with certain telephoto-like intrinsic properties, like compression and a complete absence of wide angle distortion. You might think that's a good choice for head-and-shoulders portraits because it's 100mm, a narrow angle of view, and requires the photographer to stand further away from the subject to make such a portrait, thus giving a pleasing rendition of facial features. But that's not always the case:
100mm on full frame gives roughly a 20º diagonal angle of view. Yes, that is telephoto and would be a common focal length & subject distance for pleasing head-and-shoulders portraits.
100mm on an 8x10 (that's 8 inches by 10 inches of film. Think Ansel Adams) gives about a 117º diagonal angle of view, which is equivalent to the angle of view provided by a 13mm lens on full frame.
Extreme wide angle with wide angle distortion! That exact same focal length on an 8x10 would lead to incredibly distorted head-and-shoulders portraits because the camera would need to be inches away from the subject. Terrible choice.
What term (instead of "field of view") would I use to communicate that by putting on a 24mm lens, I'm getting a wider area in my picture vs a 50mm? Like for instance during shooting, I would say "Hey I want a wider __________ to get these clouds and foreground in the picture, so I'm gonna put on my 24mm lens"?
Context is king. If you're swapping lenses on the same body, obviously a shorter focal length will give you a wider FOV. Personally I would just say "Hey I want a wider
lens" or "Hey I want a wider
shot."
Personally I would not say "I want a
wider focal length." "Wide length" is awkward phrasing.
I could say "I want a
shorter focal length" but that's kind of geeky for casual conversation amongst friends.
If I was feeling dorky I could say "hold my beer, I'm going wide!"
But in internet forums? Nobody knows what body you're using unless you're explicit about it and provide context. There's nothing inherently wide-angle about the 24mm focal length in isolation. On a m4/3 camera that's a normal lens (48mm full frame equivalent angle of view). On a compact camera that's telephoto- a Nikon P1000 @ 24mm gives a FOV equivalent to 135mm on full frame.
Hope that helps.
