Lens focal point

[NK Creative]

Hi

I have been using a Sony 6500 APS-C camera now for few years. I have the 50mm by Sony. I know that 50mm is standard and that APS-C sensors have a crop factor of 1.5x.

Does this apply to lenses made for Sony crop cameras? As in is the lens a 24mm lens with 50mm written on it to compensate for the crop factor. Same with any other lens that is made for crop cameras.

[Olaf W.]

The crop factor applies to all lenses. Your 50mm lens gives you a focal lenght of 75mm on an APS-C sensor.

[Alejandro]

21 hours ago, NK Creative said:

As in is the lens a 24mm lens with 50mm written on it to compensate for the crop factor.

If a lens says it is (for example) a 50 mm, then it has a 50 mm focal length (no mater what, though sometimes the equivalency for a Full Frame might be expressed in brochures of compact cameras rather than the real focal length of the lens for that camera).
What varies is not the focal length of a lens, but the angle of coverage (field of view) if used on a full frame camera or on a camera with an APS-C sensor. A 50mm lens on a camera with an APS-C sensor will have an angle of coverage being about the same as a 75 mm lens would have on a Full Frame Camera.

The adjoined drawing might explain better what I tried to say. (I downloaded the drawing from an article named "Crop Sensor (APS-C) Cameras and Lens Confusion", which I found at bobatkins.com)

21 hours ago, NK Creative said:

I know that 50mm is standard and that APS-C sensors have a crop factor of 1.5x.

A 50 mm focal length for a lens is usually considered (or was usually considered) the standard focal length for a full frame camera (for a camera with an APS-C sensor, a 35 mm would mostly be). That’s why there can be found so many 50 mm vintage lenses that used to be the kit lenses for 35 mm film (full frame) analogical cameras. On a camera with an APS-C sensor, a 50 mm lens would be sort of a short telephoto (having a typical angle of coverage very much used for portraits, among other things of course).

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Edited August 2, 2021 by Alejandro

[Pieter]

11 hours ago, Olaf W. said:

The crop factor applies to all lenses. Your 50mm lens gives you a focal lenght of 75mm on an APS-C sensor.

Please don't spread this confusion. A 50mm lens has a 50mm focal length no matter what sensor you put it on. Focal length is a property of the lens, not of the sensor. It's the field of view that changes due to a smaller crop from the projected image, as elegantly shown in @Alejandro's image. But smaller relative to what?

What makes me wonder @NK Creative: why do you care about crop factor? Guessing by your question, all you've ever used is your A6500 and you know what kind of images you get from the lenses you put on it. That's all that matters: crop factor is totally irrelevant to anyone who only uses APS-C cameras. It refers to an image format you've never used and can't relate to.

Edited August 2, 2021 by Pieter

[Olaf W.]

Please read my answer thoroughly. 

[Pieter]

I did, that's why I'm literally quoting it:

11 hours ago, Olaf W. said:

Your 50mm lens gives you a focal lenght of 75mm on an APS-C sensor.

No it doesn't. A 50mm lens on an APS-C sensor gives the same field of view as a 75mm lens on a FF-sensor. Key here is to not suggest the focal length changes (this is extremely confusing to beginning photographers) and to state your subject of reference (a FF-sensor). The article referenced by @Alejandro perfectly explains why your statement is so confusing.

An APS-C-user with limited experience in photography doesn't know what a 75mm lens on a FF camera looks like. He only knows what a 50mm lens on an APS-C camera looks like. To assume every photographer is able to naturally relate to FF-standards is short-sighted.

Edited August 2, 2021 by Pieter

[Olaf W.]

You are right but perhaps your more profound explanation is also confusing for a beginner.  

Many beginners think (I did as a beginner) they get the same results with a 50mm lens attached to an APS-C sensor as they did with a 50mm lens („normal focal lenght“) and an analog film camera. They don’t. 

[XKAES]

Both explanations can be confusing to different people -- especially when photographic "terms" are ill-defined and thrown around loosely.  The focal length of a lens does not change when the film/sensor size changes -- but either does the angle of view or the field of view of the lens.  It's the picture angle that's important -- and that depends/changes on the film/sensor size.  A 50mm lens will be a wide angle on some formats, a "normal" on some formats, and a telephoto on some formats.  That's why you have a 22mm on a submini, a 32mm on  half-frame/APS, a 50mm on a full-frame, a 90mm on a 120, and a 150mm on a 4x5.  They all have different focal lengths, different angles of view, and different fields of view -- but they all have the same picture angle.

Beginners (and many other, as well) need to understand that the focal lengths of their lenses must match with the format they are using -- and a "crop factor" is one way of explaining that.  It works well with people who are used to using full-frame cameras

[Alejandro]

2 hours ago, XKAES said:

Both explanations can be confusing to different people -- especially when photographic "terms" are ill-defined and thrown around loosely

?? (sorry for that)

2 hours ago, XKAES said:

It's the picture angle that's important

Forgive me, but English is not my native language, so maybe I'm misunderstanding you or not understanding you properly. I might need a thorougher explanation. I think I understand what you are trying to convey, but are you saying that a "picture" has an angle?? How come?

Anyway, I hope that with everything that has been said and explained, NK Creative's question might have been answered. Has it? It would be nice to have his feedback.

[XKAES]

First, there is a typo in my original response.  I wrote "The focal length of a lens does not change when the film/sensor size changes -- but either does the angle of view or the field of view of the lens."

That should be "The focal length of a lens does not change when the film/sensor size changes -- but neither does the angle of view or the field of view of the lens."

There is a description and a visual graphic of the differences of what we are discussing on my website:

The World's Most Complete Fujinon Large Format Lens List

 

[Pieter]

Noone suggested the angle/field of view of the lens changes (specifically: the projection angle or angle of coverage of the lens). The field of view of the picture does. To quote from your very website (which states it correctly, relating picture angle to field of view):

PICTURE ANGLE / AKA ANGLE OF VIEW or FIELD OF VIEW (in degrees): Not to be confused with the angle of coverage ... it varies depending on what film size you are using (i.e., picture size).

Anyway, this is all getting way too technical for OP and all this confusion confirms my point: unless you are using different sensor/film formats side by side, never bother yourself with such a senseless principle as 'crop factor'.

[XKAES]

You may be underestimating the interest and ability of the questioner.  And many people are quite familiar with the term "equivalent crop factor" -- lots of owner's manuals and photography books use it.

[Pieter]

I think a lack of interest is pretty evident from the lack of engagement in his/her own forum thread.