Does a RF-S lens focal length take the crop factor into account?

[aedcce]

Right now, for the EOS R cameras, there are RF and RF-S lenses.

If I were to get the RF 16mm for my R10, for example, the 1.6 crop factor would make it more equivalent to a 25mm focal length.

The RF-S lenses, however, are specifically designed for crop sensor cameras. Would I still add this multiplier or is the number the same as on the box for RF-S lenses?

[Tronhard]

Actually, I was not specifically targeting your post, simply stating my own position. 

I gave a much more detailed explanation below, which I stick with, and I like to produce reference material to underpin that.  However, since you seemed to want the short version:"

questioners sound like they'd benefit from the KISS principle."  I gave that too - but specifically targeted at the OP's precise question - I hope!

The facts are well established, the rest comes down to how those facts are presented and I see no reason for debate over that.  The main thing is the OP understands what is happening here.

[Tronhard]

questioners sound like they'd benefit from the KISS principle."  I gave that too - but specifically targeted at the OP's precise question - I hope!

The facts are well established, the rest comes down to how those facts are presented and I see no reason for debate over that.  The main thing is the OP understands what is happening here.

[ebiggs1]

"Why do you care? It has the field of view it has. There is no reason to make 35mm some standard of reference, especially if you have never used a FF camera."

Gold star answer.

[kvbarkley]

I would describe it by what it is:

                        FF                   APS-C

wide angle     less than 20      less than 15

moderately wide angle 20-30     15-20

normal                        30 - 70      20 - 40

short telephoto           70 - 90        40 - 60

telephoto                    > 90              >60

[ebiggs1]

"So how would YOU describe/label what happens when putting a lens on an APS-C body?"

I wouldn't. The lens used on any camera is just the lens used on any camera. Medium format guys don't think crop factor and neither should APS-C folks. A 28mm lens., etc., does what it does on each format and there's the end to it. It's a 28mm lens, period.

[p4pictures]

As others have said the focal length of the lens is a character of the lens. A 50mm lens used on a full-frame EOS camera is still a 50mm lens when fitted to an APS-C camera.

The confusion has come around since the focal length was used as a way to express the angle of view provided by a lens. The angle of view depends on the focal length AND sensor size. Smaller sensors like APS-C will have a narrower angle of view than a camera with a larger sensor with the same focal length lens.

As an example the RF 50mm F1.8 STM lens spec sheet lists the following:

Angle of View (Horizontal, vertical, diagonal) - 40°00′, 27°30′, 46°00′

For most photographers the angle of view is even more complex to remember and understand than a single focal length number. This is what the focal length is used.

The effect of the smaller APS-C size sensor is to reduce that angle of view, but rather than give the figures, a neat workaround is to use a crop factor or multiplier to try and make sense of the narrower angle of view. For an APS-C size sensor the crop factor is 1.6x. Meaning the 50mm lens on and APS-C camera will have an angle of view similar to an 80mm lens on full-frame camera.

Taking the RF-S 18-150mm kit lens as an example, the camera shows the actual focal length on the screen as you zoom from 18-150mm, however the angle of view captured is more like a 28.8 to 240mm lens would be on full-frame camera.

[kvbarkley]

Actually the specs are in error. They do not say that the AOV is specified for a full frame camera.

[ebiggs1]

"Smaller sensors like APS-C will have a narrower angle of view than a camera with a larger sensor with the same focal length lens"

I wouldn't say that isn't true but it isn't complete either. It does depend how big the sensor is but not all sensors stop at the 35mm FF size. The crop equivalent goes the other way as sensors get larger than 35mm size. And in that group nobody cares!

[Tronhard]

Hi and welcome to the forum:
As you can see this is a subject fraught with challenges!  I would offer the following article I wrote on the subject that is based on physics, material from a professor in photographic optics, and has been peer reviewed.
Focal Length, Sensor Size, Equivalence and Field of View 

I will simply say, for the discussion, that a lens' focal length is a physical characteristic of a lens.  It does not change, whatever type sensor is behind it, from what is written on the lens.  However, what the sensor captures does impact the final result.  This result is the called Field of View (or Field of Capture) and should always be identified as such.  The image area recorded by a smaller sensor will be smaller: however, when magnified in a screen or print to the same area or to a common size (e.g. both formats printed in an 8"x10" format), will seem to render a result similar to using a longer focal length lens.  The magnification is not done in the lens.
The top shows what is captured, the bottom shows the result after magnification of the image later

In an effort to encompass this phenomena, and explain it in terms of the lens alone, writers and reviewers have coined the term 'crop factor', and applied it to the focal length, but actually it is applied to the Field of View, and this is where the confusion begins.  The lens is not 'cropping' the image, the sensor is.  Arguably, Ernie is quite correct in saying that all images are cropped, because the image projected by the lens is actually circular - as they were in the early Kodak box cameras:
Images from and early Kodak Box camera (ref. Kodak.com)

However, the vernacular term 'Full Frame' came about as the 35mm format became a de facto standard in the mid- to- latter part of the last century - basically for its combination of decent imagery, combined with the smaller, lighter cameras and high-quality lenses that could use it.  Certainly that dominance was driven home by the proliferation of the 35mm SLR camera.  Smaller size films (and later sensors) thus became known as 'cropped'. 

To put it another way, in the context of your question: "Would I still add this multiplier or is the number the same as on the box for RF-S lenses?"  If using an APS-C camera, you multiply the focal length of ANY lens by the crop factor (RF or RF-S) to compare it to the focal length, if using a FF camera, to achieve the same Field of View .  So, a 50mm lens (be it an RF or RF-S lens type) will create a FoV equivalent to an 80mm lens on FF camera.  Conversely, if you want to put a lens on your crop-sensor camera that will yield the same "normal" FoV as a 50mm lens on a FF camera, you divide the required value by the crop factor.  Thus, to get the same FoV, 50mm/1.6 = 32mm to get a 'normal' FoV.

The name APS-C (Advanced Photo System type-C) actually comes from a move by a consortium of film makers in 1996. For a full explanation of the the format see Advanced Photo System - Wikipedia.  The format was essentially overtaken by the rise of the digital camera, and so died out pretty quickly, but was reborn as a digital sensor format.

[wq9nsc]

As others stated, lens focal length is a function of the lens design so it doesn't vary by the camera on which it is used.  But the results do and that is why I think in terms of "equivalent focal length" when using an APS-C size sensor like my little M6 M2 uses.

For decades, the most common pro or semi-pro cameras used 35mm film and digital cameras that use what is commonly called a full size or full frame sensor have a sensor size nearly identical to a 35mm film camera.  For those of us who used film for years and then full frame digital, we are used to thinking in terms of specific focal length when choosing a lens application or when considering the minimum shutter speed to reasonably avoid blur from camera shake.  For those of us who have those numbers "baked" into our brain, it is useful to use the 1.6x focal length multiplier when using an APS-C sensor so that we can make decisions based upon numbers we have a lot of experience using.

My first "real" digital was a Canon 1D Mark II which used a APS-H sensor with a 1.3X "crop" factor, close enough that I thought in terms of conversion but in reality it wasn't far enough off from full frame to make much difference.

Rodger

[ebiggs1]

"For decades, the most common pro or semi-pro cameras used 35mm film and digital cameras that use what is commonly called a full size or full frame sensor have a sensor size nearly identical to a 35mm film camera.'

Probably true for mobile users but certainly not for studio use. We never used 35mm cameras at work only when we were out on a mobile assignment. I never heard anyone say, I wonder what the equivalent FL of this lens is on my medium format camera or my 8x10 box camera. It was a term that wasn't needed and has caused so much confusion because of it.