Does an EF-S lens' focal length have the 1.6 crop factor calculated?

[bryannemarie]

For example, the kits lens that is often 18-55mm purchased with a canon rebel, since it is specifically made for crop-sensored camera, is it a 'true' 18mm focal length, just as an 18mm EF lens would be on a full frame camera (other than smaller field of view)? Or to get the 18mm focal length effect, would you still need to purchase something closer to a 10mm EF or EF-S lens? In other words, say you had two 50mm lenses, one EF, one EF-S and used them on a APS-C camera (ex. Canon Rebel T4i), would they both come up with the same image or would the EF be closer to an 80mm, while the EF-S provides a 50mm image, since the lens is created with the crop factor in mind? .

[kvbarkley]

Size of the image circle has to do with other things besides "classic" lens design.

For example, you can use an EF-S lens on a Canon R, but it restricts the image to the size of an APS-Sensor. You probably have "image" out there, but Canon cannot guarantee the quality. I imagine the field curvature goes out of whack, among other things.

[kvbarkley]

And the answer is no, a 70 mm lens is a 70mm lens. It will provide the exact same magnification. It only makes a difference when you are talking about the size of the format.

[ebiggs1]

"If this is true, then there is nothing being thrown away,..."

"It was about EF-S vs EF lenses with the same focal length dialed in and on the same APS-C camera, identically placed, seeing the exact same subject. Are the resulting images different?"

This topic which isn't difficult to understand.  It has been made difficult by some folks in the beginning seeing a difference in their photos from what they saw with 35mm film.  This whole crop factor myth is a joke and totally necessary. Medium format  and large format guys don't use it although they have it.

Let's get out of the "weeds".  A lens FL is what it is when it is manufactured.  It never changes nor can it change.  If the lens is a 70mm ef-s or a 70mm ef or a Hasselblad 70mm lens, it is a 70mm lens no matter what camera it bolts on to. The printing on the lens body is what the lens physically is.  The AOV  (angle of view) will be different but not the FL. Second, and probably the most difficult concept to get over is nothing is cropped. Nothing is thrown away. If you believe that, something must added when you go up in sensor size, if something is throw away as you go down. I am sure the larger sensor doesn't create it out of the air.

Another confusing part or at least what most people don't know is just what is a lens? They think a lens is that black tube with rings and glass and markings on it. Actually a lens is a piece of glass with curved sides for either concentrating or dispersing light rays.   WHat is FL, for camera lenses the distance between the center of a lens and its focus point. It is not a measurement of the actual length of a lens. FL tells us the AOV (angle of view). The longer the FL, the narrower the AOV will be, higher magnification. And of course, the shorter the FL, the wider the AOV will be.  This is where the "equivalent FL" or "crop factor" got its beginning. People were talked into using a crop factor, 1.6x, in favor of just learning the AOV a lot less confusing.

Hopefully this has clearned it up a bit.

[kvbarkley]

My Rebel certainly does "throw away" the part of the FF image circle that does not fit onto the smaller sensor.

[ebiggs1]

Believe what you will.  It doesn't.

[ebiggs1]

"... the part of the FF image circle that does not fit ..."

OK, if your Rebel throws away anything so does your FF.  Lenses produce a circular image which is projected on a rectangular sensor.  Some light is ignored because one is round ant the other ain't. 

[DarbyBo]

To the OP (many years later): I had the same question and this helped me.

[Tronhard]

Hi again:
To answer your question as simply as I can.  A lens focal length is a physical characteristic of the lens, and as such has nothing to do with the sensor.  So, any EF or EF-S lenses with the same focal lengths, on the same APS-C camera, should produce essentially the same results in terms of Field of View they capture.

To prove that, I did the following experiment.  I used a Canon EOS 80D, which was pointed at a boring fence but gives an easy measure of the field of view by counting the palings.  The camera was firmly mounted on a tripod and, in turn, I attached three lenses to the camera.  All lenses were at 100mm focal length:

All I have done it to use Photoshop to precisely resize the images from the original 6000x4000 resolution, without cropping, to a resolution of 3000x2000 for reduction to <5MB as required for posting

80D with EF 100-400L@100mm80D with EF100mm Macro80D with EF 18-135 IS USM@100mmWhile the first two were easy to set to exactly 100mm, the EF-S 18-135 USM took several attempts to get it at exactly 100mm but to confirm I did, here is the EXIF data from Photoshop.

They are all almost exactly the same Field of View.  I hope this answers your question.