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FORUMS Canon Cameras, Lenses & Accessories Canon EF and EF-S Lenses 
Thread started 29 Mar 2012 (Thursday) 08:56
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What is the advantage of Canon EF-S lenses over EF?

 
SkipD
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Mar 29, 2012 10:36 |  #16

Akukes wrote in post #14174322 (external link)
I know EF-S lenses are designed for certain Canon cameras (XT up to 40D), but what is the advantage of them? I was originally made to understand that the EF-S lenses took into account the 1.6x crop factor so that the EF-S 17mm-85mm was indeed effectively a 17mm-85mm equivalent and not effectively 27mm-136mm. The more I read, the more I'm beginning to feel that this is not the case. If this is not the case, then why would I want an EF-S lens as opposed to the more widely compatible EF lenses?
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Cost and weight.


Publishing this again.......

The APS-C format cameras such as Canon’s Digital Rebel series and their 20D through 60D series plus the 7D have a smaller sensor than a 35mm film frame. If you limit the lens selection to those lenses designed to fill a 35mm frame (such as Canon’s EF series lenses), you will find that there are no ultra-wide-angle lenses for the APS-C camera.

At the time of this writing, the shortest zoom lens focal length in the EF mount lens family is 16mm. There are two primes that are a bit shorter, and one of those is a "fisheye" lens. NONE of these lenses are what the average photographer would call "affordable".

To design an ultra-super-wide-angle lens such as a 10mm (non-fisheye) lens for a 35mm film camera is a VERY expensive proposition, which is why there are none.

By making some changes to the design criteria - reducing the "film" area to be covered by the lens, and allowing the lens to project deeper into the mirror box (moving the rear element of the lens closer to the "film"), it becomes much more economically possible to design lenses for the task. Thus, the EF-S family of lenses was born, the “S” standing for Short back focus.

The EF-S lens mount is purposely designed to be different from the standard EF lens mount so that you cannot mount the EF-S lenses on cameras that were not specifically designed for them. If you modified the mount of an EF-S lens to be able to put it on a 35mm film camera, there would be a high probability that the mirror would crash into the rear element of the lens at certain focal lengths (the mirrors in the APS-C cameras are significantly smaller than those in 35mm cameras and “full-frame” DSLR’s). Also, the 35mm film frame would have a dark circle around the edges and the image would be inside the circle (known as vignetting).

Now that you have some understanding of what the EF-S lenses are all about, you need to understand that focal length is focal length is focal length. An EF 50mm prime lens designed for a 35mm camera, when used on an APS-C camera, will provide you with EXACTLY the same image size as an EF-S 18-55 lens set to 50mm. If you could cobble together a mount for a Hasselblad 50mm lens and use it on a 20D, you would again have the same size image as a result.

NO CHARACTERISTIC of any lens changes when you mount it on different format cameras. Focal length (or focal length range for zooms) 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. There are some changes to the depth of field, but that is also a function of the size of the sensor or film that records the image.

EF-S lenses, by the way, will only fit on the Digital Rebel series cameras, the 20D, 30D, 40D, 50D, 60D, and the 7D as of this writing.


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Mar 29, 2012 10:46 |  #17

Let's not forget that they are usually lighter when compared to an equivalent EF lens.

Edit: Boy, I'm a really slow typist when I'm eating lunch at the same time. Great post Skip!




  
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phreaknes
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Mar 29, 2012 10:47 |  #18

Wait. I always thought that an EF-S lens was what it was on a crop. so for example

17-55mm EF-S lens on a 60D is 17-55mm focal length
24-70 EF lens on a 60D is 38.4-112mm focal length

if this isn't correct then I've got some thinking to do about my lens choices also since the EF-S design is 'closer' then what does that do to the aperture ratings I would assume that if you have a EF-S lens at 2.8 it will be 2.8 if you have an EF lens on a 60D because of design the aperture would change.

Please help and correct my thinking if I'm wrong.


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canadave
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Mar 29, 2012 10:50 |  #19

phreaknes wrote in post #14174841 (external link)
Wait. I always thought that an EF-S lens was what it was on a crop. so for example

17-55mm EF-S lens on a 60D is 17-55mm focal length
24-70 EF lens on a 60D is 38.4-112mm focal length

if this isn't correct then I've got some thinking to do about my lens choices also since the EF-S design is 'closer' then what does that do to the aperture ratings I would assume that if you have a EF-S lens at 2.8 it will be 2.8 if you have an EF lens on a 60D because of design the aperture would change.

Please help and correct my thinking if I'm wrong.

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Mar 29, 2012 10:56 |  #20

phreaknes wrote in post #14174841 (external link)
Wait. I always thought that an EF-S lens was what it was on a crop. so for example

17-55mm EF-S lens on a 60D is 17-55mm focal length
24-70 EF lens on a 60D is 38.4-112mm focal length

if this isn't correct then I've got some thinking to do about my lens choices also since the EF-S design is 'closer' then what does that do to the aperture ratings I would assume that if you have a EF-S lens at 2.8 it will be 2.8 if you have an EF lens on a 60D because of design the aperture would change.

Please help and correct my thinking if I'm wrong.

Once again, focal length is always whats printed on the Lens, so nothing changes in that regard. What changes is the field of view. The sensor is smaller so you see less of the image circle which give the impression of magnification.




  
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Mar 29, 2012 10:57 |  #21

phreaknes wrote in post #14174841 (external link)
Wait. I always thought that an EF-S lens was what it was on a crop. so for example

17-55mm EF-S lens on a 60D is 17-55mm focal length
24-70 EF lens on a 60D is 38.4-112mm focal length

if this isn't correct then I've got some thinking to do about my lens choices also since the EF-S design is 'closer' then what does that do to the aperture ratings I would assume that if you have a EF-S lens at 2.8 it will be 2.8 if you have an EF lens on a 60D because of design the aperture would change.

Please help and correct my thinking if I'm wrong.

A 17-55mm is always a 17-55mm whether it's on a crop or FF body or whether it's an EF-S or EF lens. On a crop body the field of view figures are divided by 1.6X. However perspective and depth of field are modified differently.

This question seems to come up quite regularly and Skip always answers it correctly


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SkipD
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Mar 29, 2012 11:05 |  #22

phreaknes wrote in post #14174841 (external link)
Wait. I always thought that an EF-S lens was what it was on a crop. so for example

17-55mm EF-S lens on a 60D is 17-55mm focal length
24-70 EF lens on a 60D is 38.4-112mm focal length

if this isn't correct then I've got some thinking to do about my lens choices also since the EF-S design is 'closer' then what does that do to the aperture ratings I would assume that if you have a EF-S lens at 2.8 it will be 2.8 if you have an EF lens on a 60D because of design the aperture would change.

Please help and correct my thinking if I'm wrong.

Somebody fed you with a line of total bovine excrement. :p


Taken from my article above:

NO CHARACTERISTIC of any lens changes when you mount it on different format cameras. Focal length (or focal length range for zooms) 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. There are some changes to the depth of field, but that is also a function of the size of the sensor or film that records the image.


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amfoto1
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Mar 29, 2012 12:06 |  #23

phreaknes wrote in post #14174841 (external link)
Wait. I always thought that an EF-S lens was what it was on a crop. so for example

17-55mm EF-S lens on a 60D is 17-55mm focal length
24-70 EF lens on a 60D is 38.4-112mm focal length

if this isn't correct then I've got some thinking to do about my lens choices also since the EF-S design is 'closer' then what does that do to the aperture ratings I would assume that if you have a EF-S lens at 2.8 it will be 2.8 if you have an EF lens on a 60D because of design the aperture would change.

Please help and correct my thinking if I'm wrong.

Ok, prepare to be corrected...

EDIT: SkipD is right.

17-55mm on 60D is 17-55mm
24-70mm on 60D is 24-70mm

Focal length doesn't change. If you were switching back and forth between cameras - such as the crop sensor 60D and the full frame 5DII - the format of the image is all that's changed. The way the lens "behaves" on the different formats changes. But the focal length remains the same in either case. .

It just so happens the 17-55mm is an EF-S lens, so it's designed to only fit onto the 60D and other crop sensor Canon cameras (300D or Digital Rebel/20D and later models). If Canon happened to offer an EF 17-55mm lens for full frame cameras (the closest is the EF 17-40/4L), fitted to 60D it would perform exactly the same way as the EF-S lens.

This really is nothing new... we saw the same thing with different film formats, too, those of us who used several different ones....

A 90mm lens is a wide lens on a large format film camera such as a 4x5" view camera and it would be an ultra wide, if it existed, on a larger format such as 8x10. A 90mm lens on a medium format camera such as a 6x7cm behaves as a standard or normal lens. Meanwhile, a 90mm lens on a 35mm film camera acts as a short telephoto. The focal length hasn't changed at all... but the way it behaves on the various formats changes. (Note: the lens would probably need to be redesigned for each case, so that it has a large enough image circle to cover the entire image on the film or on a sensor. But the focal length remains the same.)

The same is true across all focal lengths.... 50mm would be an ultrawide lens on 4x5, a wide on medium format, is a normal on 35mm film or full frame digital, and acts as a short telephoto on smaller formats such as crop sensor digital or half-frame or APS film cameras.

At the other extreme... a 300mm is a normal or standard lens on an 8x10" view camera, a short telephoto on a 4X5, moderate telephoto on medium format, strong telephoto on 35mm/FF, and a super telephoto on anything smaller format such as crop sensor DSLRs.

It's the same with different formats of film or with different digital camera sensor formats.

The biggest problem with early digital cameras, the vast majority of which used a crop sensor that's smaller than a 35mm film images, was that there were no wide angle lenses to use with them. They were trying to use the same lenses that had originally been designed for 35mm film... a 24x36mm image that's now often refered to as "full frame". A 17mm lens was super wide on that film camera, but was only moderately wide on the approx 15x22mm size image of most DSLRs being offered.

So, manufacturers developed really wide lenses to meet this need. Canon calls theirs EF-S and has gone to the extra step of making it a special mount that won't allow the lens to even be mounted onto full frame cameras. If you look at EF-S and other crop camera specific lenses, you'll notice that most of them are concentrated toward the wide angle end of things. (More and more, we are also seeing crop design lenses in longer focal lengths too, where they can be smaller, lighter and/or more economical than full frame design lenses. The EF-S 55-250 and EF-S 60mm macro lenses are some good examples of this.)

Your 60D and other Canon crop sensor cameras have a bit of an advantage over full frame models. You can use any and all 70 million EF and EF-S lenses Canon has manufactured over the past 25 years. You also can theoretically use any and all third party lenses made for Canon EF mount cameras during that time. (Note: 3rd party lenses might fit physically, but there can be software/hardware compatibility issues, such as a lens that won't focus or causes the camera to lock up when it tries.)

A full frame camera, on the other hand, cannot use the EF-S, is limited to EF lenses and third party lenses designed for FF only (which is still a pretty darned good selection, tho).

Finally, some lenses are what is called a "retrofocus" design. This means that they move the rear group of the lens to focus and/or zoom. This is often a design that's used with ultra wide lenses. So even though the lens register or distance from the mounting flange to the film/sensor plane doesn't change, the rear elements of the lens might actually protrude inside the camera. A lens designed for a crop sensor camera fitted onto a FF camera might protrude too far into the FF camera at certain focus or zoom settings, interfering with and possibly damaging the mirror that's moving up and down in there each time an exposure is made. Canon uses the EF-S mount in an effort to prevent installing a crop lens onto a FF camera, but other manufacturers don't.

For example, my Tokina 12-24mm lens, which is designed for crop sensor cameras, will fit just fine onto my FF 5DII camera. And it will work from 24mm to as wide as 18 or 19mm zoom setting before I start to see vignetting (a shadow, if you will) occur. I won't use it any wider, just in case it might interfere with the camera's mirror. Since the image is vignetting anyway, there's no reason for me to take that risk. I have heard that the Tokina 11-16mm lens can be used at the 16mm setting only, but there is some vignetting. I don't know about other third party "crop" lenses.

In the end, if you never used 35mm film or full frame digital cameras, if your 60D with it's crop sensor is the first SLR you've owned and used, forget all the math and just buy the lenses that will do what you need them to do. The 17-55/2.8 IS is a very good choice. The 24-70/2.8L is excellent too. They just cover different focal length ranges and which one you might want has more to do with which one fits in best with the other lenses in your kit or which one meets your particular needs the best.


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Mar 29, 2012 12:16 |  #24

Its a pity that SkipD's and amfoto1's replies can't be automated responses to these sort of questions it would save a lot of hassle and confusion


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Mar 29, 2012 13:32 as a reply to  @ troutfisher's post |  #25

Finally, some lenses are what is called a "retrofocus" design. This means that they move the rear group of the lens to focus and/or zoom. This is often a design that's used with ultra wide lenses. So even though the lens register or distance from the mounting flange to the film/sensor plane doesn't change, the rear elements of the lens might actually protrude inside the camera.

Actually, the purpose of retrofocus lens design is to avoid protruding into the camera.

Normal focusing would move the lens elements backwards to focus closer. In "retro" focus design the rearmost lens elements don't move at all or in some cases even move forward.


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Mar 29, 2012 13:33 |  #26

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Mar 29, 2012 13:58 |  #27

troutfisher wrote in post #14175290 (external link)
Its a pity that SkipD's and amfoto1's replies can't be automated responses to these sort of questions it would save a lot of hassle and confusion

I guarantee you that I don't retype that each time it's posted.  :p


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Mar 29, 2012 14:05 |  #28

Is their image circle actually smaller? I've seen people with EF-S lenses on their 5Ds and wondered if they're not cropping.


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Mar 29, 2012 14:21 |  #29

gonzogolf wrote in post #14174445 (external link)
As has been mentioned above, its about cost. An Ef-S lens doesnt have to project as big an image circle because its for a smaller sensor. This allows for a smaller lens and its generally cheaper to produce than an equivalent lens for full frame.

cheaper and in some cases sharper! The EF-S design actually helps in image resolution for the smaller sensor. Here is one explanation from POTN member "Wilt" which I have copied


"A truism of photography is that as a lens has to cover a larger image circle, its resolution is spread over a larger area. A smaller format lens like for the 135 format has higher measured lines-per-millimeter (typically 50-80 line pairs per mm) detail resolution than a lens for 4x5 sheet film (30-40 line pairs per mm)...and a microfilm lens which covers the tiny microfilm format has higher lines-per-millimeter (250 line pairs per mm) than 135 format lens (80-120 line pairs per mm for a spectacular lens!).
High resolution + large image circle coverage typically comes only at a super high price...what the military pays for high altitude reconnaissance lenses that cover 8x10 film, for example.

And that is why APS-C lenses with 15x22mm coverage can often have higher test resolutions than the equivalent FL lens which covers the larger 24x36mm FF format.

The benefit in EF-S is that a lens with smaller image circle the light rays will stike the sensor more perpendicularly and not obliquely."
(end quote)




  
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Mar 29, 2012 15:16 as a reply to  @ watt100's post |  #30

And that is why APS-C lenses with 15x22mm coverage can often have higher test resolutions than the equivalent FL lens which covers the larger 24x36mm FF format.



The operative phrase there is "test resolution."

The larger image--even with less lens resolution--can often still put more image detail into the frame and end up with more detail in the final image. We've seen plenty of large format images with incredibly fine detail from "inferior" systems.

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What is the advantage of Canon EF-S lenses over EF?
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