EF-S Lenses

Made a quick skim over the sticky and maybe I missed someone answering this, however. (I also read over the wiki page about it too)


I know that if you put an EF lens on a APS-C the focal length isn't "true" to what it says on the lens. So, on an EF-S lens does the same apply? Or does it stay "true" to the markings on the lens?


Ergo, EF-S 18-55mm lens + 50D = 18-55mm.

The focal length of a lens always stays the same.
EF-S indicates that the lens is designed for the smaller APS sized sensor.
The answer is Yes, the focal length stays true.

The focal length stated on the lens is ALWAYS the focal length of the lens, no matter what body it is mounted on.

Any 18-55 lens, whether it be an EF or EF-S lens, is 18-55 mm.

Focal lengths of lenses do not change. The only thing that changes between an APS-C camera and a "ful frame" camera is the field of view the sensor can capture.

Syntaxxor wrote in post #11466573
I know that if you put an EF lens on a APS-C the focal length isn't "true" to what it says on the lens. So, on an EF-S lens does t

The world was screwed up by how journalists wrote about the topic, and by what the camera manufacturers claimed on their cameras!!!

The truth is that 'APS-C with 50mm lens captures a FOV which is equivalent to the FOV obtained with a FF camera with an 80mm lens'. (and any other equivalence like 10mm vs. 16mm, as defined by the ratio factor of 1.6x) But if someone had no experience with FF, the comparison is a meaningless one. As everone has stated, FL never changes...the FOV which is limited by the size of the frame is the ONLY thing to change (and the DOF changes, due to the use of a short or longer FL to obtain the same FOV)

Syntaxxor wrote in post #11466573
I know that if you put an EF lens on a APS-C the focal length isn't "true" to what it says on the lens. So, on an EF-S lens does the same apply? Or does it stay "true" to the markings on the lens?

What you "know" just ain't so. As a side note, that's also the proposed title of a book my Dad wanted to write about things I told him as a kid.

Please read the following article VERY CAREFULLY and with an open mind. You will learn the truth about the "crop factor" and the actual truth is FAR from what you presently think it is.

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The "crop factor" is a reference number that relates to the difference in film or sensor size (known as the camera's "format") between two cameras like the Canon 7D and a 35mm film (or a so-called "full-frame" digital) camera. Let me list the facts:

35mm film cameras and so-called "full frame" DSLRs have a film frame or sensor size of approximately 24mm X 36mm, while the Canon 7D has an APS-C sized sensor, measuring approximately 14.9mm X 22.3mm. The other Canon APS-C format cameras - starting with the D30 in the year 2000 and progressing through all of the "digital Rebel" xxxD series, the xxD series, and today's 7D - all have sensors that are sized similar to that in the 7D.

When camera manufacturers started designing digital SLRs (DSLRs), they decided that the DSLR bodies should be about the same physical size and configuration as their 35mm film SLRs. For that reason, they concluded that they could use the line of lenses they already had for their 35mm SLRs on the new DSLRs.

All lenses designed for 35mm film cameras project an image circle onto the film that covers a 24mm X 36mm rectangle. The 35mm camera records the portion of that image circle that is defined by the opening behind the shutter for the film (24mm X 36mm in size). A digital SLR with an APS-C sized sensor only records the smaller area (approximately 14.9mm X 22.3mm) of the image circle projected by the same lens.

When you put a 100mm lens on a 35mm film camera and make a photograph, then put the same lens on a DSLR such as the Canon 7D and make a similar photograph - same subject, same position for the camera, and same focal length - and then enlarge both photographs to the same size print (4 X 6 inches, for example), it will appear as though the photo from the Canon 7D was taken with a longer lens. That is because the image recorded by the Canon 7D was of a SMALLER PORTION of the image circle projected by the lens - cropped, if you will - compared to the image recorded by the 35mm camera.

The special lenses made by Canon for the 7D (and other Canon APS-C cameras starting with the 300D - the first Digital Rebel) are called the EF-S series. These project a smaller image circle, making the lenses less expensive to design and produce in wide-angle and extreme wide-angle formats. The EF-S lenses also project deeper into the camera than the EF specification allows (the "S" referring to "Short back focus), allowing for less expensive wide-angle lens designs. However, an EF-S lens set to 40mm will produce the exact same image as an EF lens set to 40mm if both lenses are used on the same APS-C format body and both lenses are focused at "infinity". Focal length is focal length, period.

Now to the primary point that I want to make: NOTHING about lens EVER CHANGES when you put it on different format cameras. Focal length never changes. Aperture range never changes. The only thing that would change is the apparent field of view, and that change is not a function of the lens but it is a function of the size of the sensor or film that will record the image.

The "crop factor" calculation for "35mm equivalent focal length" has only one valid use. That is for comparing the field of view of lenses used on two different format cameras.

Here's one common example: Joe took a photo of Mount Rushmore with a 35mm camera from a particular place using a 200mm lens. You want to replicate that photo with your Canon 7D. What focal length do you need to do that from the same location that he took his photo? Divide the 200mm by 1.6 and you get the answer - 125mm.

Here's another popular example: Mary Sue has been using a Canon SX120 IS point-n-shoot camera and is wanting to use a Canon 50D DSLR. She is, of course, interested in what focal lengths she would need to keep the versatility of the SX120 camera's 10X super-zoom lens. The SX120 lens is actually a 6.0mm to 60.0mm lens, but the advertising also shows the "35mm equivalent" focal length range as 36mm to 360mm. To know the focal lengths needed for the 50D, merely divide the "35mm equivalent" values by 1.6. In other words, Mary Sue would need 22.5mm on the short end and 225mm on the long end for the 50D to have the same field (angle) of view coverage as her SX120 IS camera.

The "crop factor" is NOTHING MORE than a REFERENCE between the two camera formats that lets you compare the field of view of particular focal lengths between the two formats.

The "crop factor" (as related to using lenses essentially designed for 35mm SLR cameras) is always given assuming that the 35mm format (24mm X 36mm) is the reference master. Something to realize, though, is that the 35mm film format is not, never has been, and never will be the "master" format against which all other camera formats are referenced. It is simply the format of the cameras that have also evolved into today's commonly used digital SLRs.

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Very well written Skip. This should be stickied.

Mk1Racer wrote in post #11467965
This should be stickied.

+1

Syntaxxor wrote in post #11466573
I know that if you put an EF lens on a APS-C the focal length isn't "true" to what it says on the lens. So, on an EF-S lens does the same apply? Or does it stay "true" to the markings on the lens?

And don't forget, an EF-S won't physically fit on a Full-Frame sensor body anyway.

SkipD wrote in post #11467189
What you "know" just ain't so. As a side note, that's also the proposed title of a book my Dad wanted to write about things I told him as a kid.

Please read the following article VERY CAREFULLY and with an open mind. You will learn the truth about the "crop factor" and the actual truth is FAR from what you presently think it is.
...

I think you are being a bit harsh and focusing on his words while ignoring his thoughts. Like many people who came from the old 35mm world, lens size equated to distance in their mind because of the constant film size. That got tossed with the C and H sensors. There are polite ways of stating that ratios are no longer constant across cameras and lens size is only one factor in the formula.

Great article Skip. This is a must read for anyone with questions about crop vs. FF.

JimmyJam wrote in post #11468138
And don't forget, an EF-S won't physically fit on a Full-Frame sensor body anyway.

This is why I thought there was a difference. I figured if it didn't fight, then it didn't fit for a reason.

Thanks for the answers! Now I want a lens that goes down to 10mm for landscaping instead of my kit lens

Syntaxxor wrote in post #11468823
This is why I thought there was a difference. I figured if it didn't fight, then it didn't fit for a reason.

EF-S does not fit FF bodies for two reasons...

1. The rear element of the lens may intrude into the FF body too far, and the larger reflex mirror of FF could strike the lens (bad!)
   
2. The image circle is too small to fill the 24x36mm sensor

Wilt wrote in post #11468850
EF-S does not fit FF bodies for two reasons...

1. The rear element of the lens may intrude into the FF body too far, and the larger reflex mirror of FF could strike the lens (bad!)
   
2. The image circle is too small to fill the 24x36mm sensor

I always get curious with that... It it "could" and it has happened before, shouldn't people be saying it "would?"
everytime i see that statement i assume YMMV with each FF paired with EF-S (if it did mount)

:p

Bleufire wrote in post #11469778
I always get curious with that... It it "could" and it has happened before, shouldn't people be saying it "would?"
everytime i see that statement i assume YMMV with each FF paired with EF-S (if it did mount)

:p

If you modify the mount so that the 55-250mm EF-S lens could be mounted to a FF body, at 250mm FL the lens will certainly not hit any optics! In fact even at 55mm it would not hit. 'Could' is the correct word to use, because striking the lens primarily happens at UWA focal lengths. Certain zoom lenses strike the mirror at the shortest 2-3mm of ots range, but not at any of the longer FL of the zoom's range.