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What is the difference between EF and EF-S lenses and what is STM?

 
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Registered: ‎12-02-2012

Re: What is the difference between EF and EF-S lenses and what is STM?

[ Edited ]

Hi.

 

EF lenses work on both types of Canon DSLR; full frame and crop sensor cameras.  Some are affordable and some are very expensive.

 

EF-s lenses only work on crop sensor cameras, and are consumer grade, affordable lenses.  

STM is just a quieter focus motor in a lens. People who do a lot of video like that, because you are less likely to hear the sound of the lens focusing recorded in your videos.  Ultrasonic (USM) focus is the other good focus motor, and it is pretty quiet too, and it is faster for sports, etc...  I would not worry much (or at all) about getting STM over USM unless you are shooting a lot of video and you are pretty particular about it.

Full Frame cameras.  Full frame cameras have a sensor equivalent to the old 35mm film size. The lenses will all give you the field of view stated on the lens, so 50mm will really be 50mm, 35mm is 35, 200 is 200, etc.  Full frame cameras include mostly pro and advanced enthusiast models such as 1Dx, 5D3, but there is also the more affordable 6D (which I use).

Crop cameras.  Crop sensor cameras have a smaller sensor.  The sensor is smaller than the image cast upon it, so the image splashes out around of the edges of the sensor.  This means the image is basically cropped down and you lose the edges, which is like zooming in on every shot, once the image is displayed at full size. The "zoom factor" is 1.6x the normal focal length of the lens, so a 100mm lens will give you an image that appears to be 160mm, a 200mm lens will give a field of view like a 320 lens, etc...  Crop cameras include the entry level cameras like Rebel T5, and the next step up like Rebel T5i, T6i, etc., and then the next step up, the 70D, and finally the high-end 7DII.

L lenses.  EF lenses are further divided into regular lenses and "L" lenses. The "L" lenses are higher quality both in optics and in construction, and some of them are to some degree weather resistant (not waterproof!). And they are much more expensive.  They have red rings on the ends.

Scott

Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites

Why do so many people say "FER-tographer"? Do they take "fertographs"?
Esteemed Contributor
Posts: 3,443
Registered: ‎06-11-2013

Re: What is the difference between EF and EF-S lenses and what is STM?

It may help to understand "why" there are both EF vs. EF-S lenses and it has to do with making cameras economically more affordable so that more consumers can buy them.

 

EF lenses are the original EOS lenses designed for 35mm film cameras and full-frame digital cameras (a "full frame" digital camera has a sensor which is the same size as a single frame of 35mm film.)  It's about 36mm wide by 24mm tall.  Incidentally, it's called "35mm" because that's the width of the film spool... including the perforated edges that ride on the film sprockets in the camera.  In other words the exposed area may be only 24mm tall... but there's 12 more millimeters for the perforated edges.

 

All lenses are, of course, round... not rectangular.  But you get a rectangular image out of the camera.  This is because the lens is projecting an image of your scene into the camera and that projects a round "spot" or image circle.  The sensor is in the middle of that circle, but since the sensor is rectangular, it only detects the light which happens to land directly on the sensor surface.  Anything that spills off the sides of the sensor isn't captured.  What's important is that the image circle being projected into the camera has to be at least as large as the diagonal measure of the sensor itself... that's 43.3mm from corner to corner.  The image circle is actually a little larger than that.

 

But full-frame digital sensors are expensive.  Canon realized that they could use a slightly smaller sensor and produce cameras that are more affordable.  These smaller sensor measure about 23mm wide by about 15mm tall (these are not exact dimensions... but close.)   BTW, this happens to be the size of a single frame of APS-C film.  APS-C stands for "Advanced Photo System - Classic" size.  These were handy little "drop in" film cartridges designed to be very convenient for consumer use.  When digital cameras use sensors in that same size, they are referred to as "APS-C" size sensors (even though we aren't actually using APS-C film.)

 

Effectively this means even more image spills off the sides and less image lands on the sensor.  It has the effect of taking an image with a full-frame sensor, but then "cropping" the image so you only save the area in the middle.  For this reason they call it a "crop frame" sensor and the crop factor happens to be about 1.6x.  There are other crop-factor size cameras as well, but for the DSLR, the APS-C size is the most popular by far.  You can get APS-C size sensor DSLR cameras from Canon... and just about every other brand of DSLR on the market.

 

What does this have to do with your question on lenses?  Everything!

 

Canon realized that since quite a bit of image is simply spilling off the sides of the sensor and isn't captured, they could produce lenses that project smaller image circles.  Doing this would require lenses that have smaller "glass" elements.  Some optical problems are reduced because the glass elements are smaller and don't need to be as thick. That also means they don't need as many corrective elements in the lens.  The lens gets smaller, lighter and substantially less expensive to manufactur and yet... you get (here's the best part) the SAME quality images (you don't sacrifice quality to do this.)  This was yet another way to make DSLR cameras more affordable to the consumer market.

 

This smaller, lighter, and more affordable lenses are called... EF-S lenses.

 

There is a trade off... remember that these lenses project a smaller image circle and are desgined specifically for use on DSLR camera bodies that have APS-C sensors.  That means you cannot use them on DSLR bodies that have "full frame" sensors.

 

Also... since a primary motivation of producin these lenses is cost reduction (so they can be sold at prices that more consumers can afford) there are some other areas where they reduce costs as well.  For example... high end lenses may have more aperture blades for a more rounded aperture opening.  They may have a better "build" quality.  They may be "weather sealed".   There's a market where this is exactly what the consumer wants (and it's a big market.)  Pros and advanced amateurs may be more demanding in these areas and refuse to sacrifice to save money.  You can still mount an EF lens on an APS-C camera.  Canon's very best quality lenses get the "L" designation.  The "L" is always appended to the foacl ratio value. (e.g. EF 70-200mm f/2.8L IS USM II".  Canon colors the "L" red and they paint a red stripe around the end of the lens.  But in order for a lens to qualify as an "L" grade lens it has to be usable on any EOS camera... not just the APS-C cameras.  For this reason you can't find an EF-S "L" lens.

 

Every EOS camera can use EF lenses.  No exceptions.

 

Every EOS camera that has an APS-C sensor (with the exception of the 10D) can use EF-S lenses.  They can also use EF lenses.

 

As for motor types, there are three major motor types..

 

1)  Conventional motors (which are the slowest and also the noisiest)

2)  USM motors (UltraSonic motors -- which tend to be very snappy and also very quiet)

3)  STM motors (Stepper Motors -- which are much faster than conventional motors, but not quite as fast as USM motors.  They were, however, designed to be particularly quiet so that the noise of the focusing motor would be very difficult to detect when recording video.)

 

See:  http://www.usa.canon.com/cusa/consumer/standard_display/Lens_Advantage_Perf

 

 

Tim Campbell
5D III, 5D IV, 60Da
Respected Contributor
Posts: 1,915
Registered: ‎02-26-2015

Re: What is the difference between EF and EF-S lenses and what is STM?

While STM is a focus motor it also indicates the newest consumer grade lenses from Canon. In addition to adding the new focus motor Canon updated the optics in STM lenses. Modern design and manufacturing gives STM lenses image quality that rivals first generation pro level L lenses from just a few years ago. So when you purchase a Canon camera with an STM kit lens there is no reason to immeadiately go out and spend more money on a new lens. That is a big advantage for Canon users now.

Esteemed Contributor
Posts: 4,289
Registered: ‎06-25-2014

Re: What is the difference between EF and EF-S lenses and what is STM?


TCampbell wrote:

 

But full-frame digital sensors are expensive.  Canon realized that they could use a slightly smaller sensor and produce cameras that are more affordable.  These smaller sensor measure about 23mm wide by about 15mm tall (these are not exact dimensions... but close.)   BTW, this happens to be the size of a single frame of APS-C film.  APS-C stands for "Advanced Photo System - Classic" size.  ...


So Ken Rockwell's contradictory etymology is bogus?

Bob
Boston, Massachusetts USA
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Esteemed Contributor
Posts: 3,443
Registered: ‎06-11-2013

Re: What is the difference between EF and EF-S lenses and what is STM?

Though Ken Rockwell is often entertaining (and often designed to provoke reactions), he's talking about APS "film".  The "APS-C"-sized digital sensor (which isn't film) has nothing to do with film and the only thing in common is the dimensions of the "frame".

 

 

Tim Campbell
5D III, 5D IV, 60Da
New Contributor
Posts: 2
Registered: ‎04-24-2015

Re: What is the difference between EF and EF-S lenses and what is STM?

[ Edited ]

Thank you Scott, Tim and others that have posted a response to my question. The responses are very helpful and will help me make a decision as to what my next lens purchase is. I printed yours, Tim and Scott, thank you.

 

I used to shoot film back in the 80's & 90's and put my camera (a Canon 10S w/a Canon 28-105 lens) down and have not shot anything, on a regular basis, in over 15-20 years. If you remember the10S is an EOS body, I believe after the 600 series and had a bar code reader to set up the camera, according to a book of sample photos, displaying barcode   Well I have been bit by the bug, once again, and am starting to put together a digital kit. My first purchase was a lens I have been wanting for a really long time, a Canon EF, 70-200, f2.8, IS II, of which Canon is very proud of. I have shot with the first in the series and have wanted one ever since. Now for the body, I am looking at the Canon 7D Mark II and the 70 D, but leaning towards the 7D Mark II. 

 

Tim, what do you think of the, Canon 60Da?  Do you use it to shoot Astrology?

VIP
Posts: 9,051
Registered: ‎12-07-2012

Re: What is the difference between EF and EF-S lenses and what is STM?

[ Edited ]

" Do you use it to shoot Astrology?"

I doubt it but maybe.  No, just kidding, he uses it for astronomy.

Anyway another point since you said you bought a fantasticly wonderfull, my very favorite, lens the EF 70-200mm f2.8 L II.

EF-S lens are not in the same class as this lens.  There are no "L" lenses in the EF-S line. I maintain it is best to keep you outfit equal in quality.  It just works better that way.

 

You can't be thinking 70D and 7D Mk II in the same sentence?  Go for the 7D Mk II.  IMHO, of course.

A lot less stuff for 2018 but still a lot of Canon stuff. Along with, a lot of other stuff.
Respected Contributor
Posts: 1,838
Registered: ‎12-02-2012

Re: What is the difference between EF and EF-S lenses and what is STM?

The 70-200 f2.8 L Mk.2 is a truly lovely lens. I am still blown away every time I look at a batch I shot with it. It was love of this lens that made me go full frame. (Well, that and the better IQ in low light at hih ISO). The 70-200 range was often a little too long for everyday shooting when mounted on my old crop camera, being cropped in by 1.6x on every shot. It worked great on sports, etc., but for much other shooting, 70mm x 1.6 = 112mm was just too long., and there were many occasions when it simply meant I could not use it. Now on full frame, 70-200 really is 70-200 and I use the lens a lot more.

What will you be shooting?
Outdoor daylight shots or indoors/nighttime?
Fast action or slow/stationary things?
Smashing the camera against rocks in the rain and abusing it or mostly average use?

It is possible you may want to go full frame depending on some of the answers above. And even if crop is right for you, you may not get much benefit from the 7d2, all depending on what /where and when you shoot.

Scott

Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites

Why do so many people say "FER-tographer"? Do they take "fertographs"?
Esteemed Contributor
Posts: 3,443
Registered: ‎06-11-2013

Re: What is the difference between EF and EF-S lenses and what is STM?


TitanSword wrote:

 

Tim, what do you think of the, Canon 60Da?  Do you use it to shoot Astrology?


There's a joke that says if you want to make an astronomer angry... just call him an astrologer.

 

I tell people at the planetarium shows that if they call me an astrologer, I'll respond by giving them bad relationship advice, bad career advice, bad financial advice, etc. etc.  ;-)

 

On the serious side... I love the 60Da, but it helps to understand what sets it apart.

 

Prior to my 60Da and even my 5D III, I had a a 5D II (actually I still have that camera).  I was at a friends house using his observatory and he had shown me an image that another club member had taken only the previous evening using the same telescope -- but with a 60Da.   Since I had all the info and access to the same scope in identical conditions, I thought why not take some exposures of the same image and see what we get using a 5D II (KNOWING that a 5D II body's ISO sensitivity is significantly better than a 60D.)

 

We took the same image at the same ISO for the same duration and I got... practically NOTHING showing up.  Surprised by this, I doubled the exposure and tried  again.  This time... still very little.  I could see the object, but it was very weak compared to what the 60Da captured (in half the time).  So... I doubled the exposure again (now I'm running an exposure which is 4x as long).  Now I'm finally starting to see the object, but have to confess that the image out of the 60Da looks better.  

 

The following day I did research on the 60Da and within a week I ordered one of my own.

 

Here's what's going on...

 

When people talk about how great the colors look on various cameras, you have to remember that there's no such thing as "color" in the Universe.  This is an imagination of the human brain.  The visible portion of the eletromagnetic spectrum runs from roughly 400nm on the short end (blue) to 700nm on the long end (red) with green being half-way in between (about 450nm).  But it turns out your eyes are not actually equally sensitive to the colors of the visible spectrum.  Human eyes are highly sensitive to green... but not particularly sensitive to blues or reds.   

 

A camera sensor (without engineers doing anything special) would normally have somewhat equal response to all these wavelengths.  This creates a problem because the job of the camera isn't to image what's REALLY there... it's supposed to image what a HUMAN eye would see.  To compensate, the sensor has twice as many photo-sites on the sensor which are sensitive to "green" as compared to the number sensitive to red or blue.  And as if that isn't enough... it also using an IR block filter which gently ramps the amount of red light being blocked started at only 500nm... and increasing steadily until it reaches 700nm (at which point it pretty much cuts off all light.)

 

Here's where this ties into astrophotography:  The most common element in the universe is hydrogen -- being about 70% of all normal matter in the universe.  Hydrogen atoms emit energy photons following something called the "Balmer" series where they pump out phons that have wavelengths in a fire-engine red color (656nm), followed by a sky-blue color, followed by a deeper blue, and so on.  You can see it here:   http://en.wikipedia.org/wiki/Balmer_series

 

When we capture images of deep-space objects (particularly emission nebula) they are PROBABLY most strongly glowing in the Hydrogen alpha wavelength... that fire-engine red color that has a wavelength of 656nm.  

 

But the human eye isn't supposed to be very sensitive to that wavelength, so normal cameras are blocking about 80% of the light at that particular frequency.  This means when you take a photograph of a nebula rich in Hydrogen alpha (which is most of them) you end up having to take a MUCH longer exposure to compensate for the fact that the camera is deliberately working to block the very wavelength of light that you want to collect.

 

The 60Da still has an IR cut filter... but rather than starting to gently block reds at 500nm and increasing the block until it finally reaches full cut-off at 700nm, the filter is designed to block almost nothing until it reaches 700nm and then do a very agressive hard-cutoff (rather than gently sloping increase of a normal filter.)

 

That's why my friend's 60Da could capture a better looking image in less than 1/4 of the time it took my 5D II.

 

If you use the 60Da to take "normal" terrestrial photos, you'll notice everything looks quite "warm".  You can back this off via white balance (of course you'd do this for every shot you take).  As such, the 60Da isn't well-suited for normal terrestrial photography, but it's fantastic for astro-imaging.

 

 

Tim Campbell
5D III, 5D IV, 60Da
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