Crop Sensor Shows no Difference between Full Frame and EP-S Lens

[paulsiegenthal]

Hi,

I made two photos on a Canon 80D using a

a. Canon EP 100 Macro lens and

b. Canon EP-S 55-250 lens

Both times I focused on 100mm. I don´t see any difference. One should be cropped?

Any explanation? 
Thanks

[Waddizzle · Accepted solution]

Your results are correct. Focal length describes a physical characteristic of the lens. When you use a EF. 100mm prime, or an EF-S 55-250nn set at 100mm, the image circle projected onto the image sensor will be almost identical. 

The primary diffference between EF and EF-S lenses is the size of the image circle projected by the lens. An EF lens projects an image that is wide enough to cover a full frame sensor, and more than cover an APS-C sensor.

An EF-S lens projects and image circle that is just large enough to cover an APS-C sensor, but not fully cover a full frame sensor.

[ScottyP · Accepted solution]

The camera crops the lenses. Not the other way around. A 100mm lens on an 80d is a 100mm lens on an 80d no matter what mount the lens has. 

A 100 mm lens on a FF body will have a wider field of view than a 100mm lens on a crop body. 

A FF lens on a crop sensor projects an image circle bigger than a crop sensor, so some of the image laps over the edges of the sensor and that excess outside edge of the image is therefore lost. The small sensor basically cropped it off by not being large enough to take it all.   An EF-s lens is made for crop cameras and it projects a smaller image circle that is matched to the smaller sensor so less of that cropping occurs. 

Full frame EF lenses can mount on either add Or crop bodies. EF-s lenses are made so they physically won’t mount on FF bodies because their rear elements may protrude back into a FF body too far and would perhaps hit the mirror in a FF body.  In any event if you do manage to jam an EF-s lens onto a FF body the image circle the lens projects onto the sensor will be too small and your picture will be a circle in the middle of a black rectangle. 

[Waddizzle · Accepted solution]

Here is another image that might help clear it up.

The image projected by an EF-S lens is a subset of the image projected of an EF lens.  Your EF lens projects an image the size of the full frame image above.  Similarly, the EF-S projects and image the size of the APS-C image above.  Its’ image would not include the much wider view projected by the EF lens.

An APS-C sensor would not see any difference between the image circles projected by the two lenses

[Waddizzle · Accepted solution]

Your results are correct. Focal length describes a physical characteristic of the lens. When you use a EF. 100mm prime, or an EF-S 55-250nn set at 100mm, the image circle projected onto the image sensor will be almost identical. 

The primary diffference between EF and EF-S lenses is the size of the image circle projected by the lens. An EF lens projects an image that is wide enough to cover a full frame sensor, and more than cover an APS-C sensor.

An EF-S lens projects and image circle that is just large enough to cover an APS-C sensor, but not fully cover a full frame sensor.

[ScottyP · Accepted solution]

The camera crops the lenses. Not the other way around. A 100mm lens on an 80d is a 100mm lens on an 80d no matter what mount the lens has. 

A 100 mm lens on a FF body will have a wider field of view than a 100mm lens on a crop body. 

A FF lens on a crop sensor projects an image circle bigger than a crop sensor, so some of the image laps over the edges of the sensor and that excess outside edge of the image is therefore lost. The small sensor basically cropped it off by not being large enough to take it all.   An EF-s lens is made for crop cameras and it projects a smaller image circle that is matched to the smaller sensor so less of that cropping occurs. 

Full frame EF lenses can mount on either add Or crop bodies. EF-s lenses are made so they physically won’t mount on FF bodies because their rear elements may protrude back into a FF body too far and would perhaps hit the mirror in a FF body.  In any event if you do manage to jam an EF-s lens onto a FF body the image circle the lens projects onto the sensor will be too small and your picture will be a circle in the middle of a black rectangle. 

[Waddizzle · Accepted solution]

Here is another image that might help clear it up.

The image projected by an EF-S lens is a subset of the image projected of an EF lens.  Your EF lens projects an image the size of the full frame image above.  Similarly, the EF-S projects and image the size of the APS-C image above.  Its’ image would not include the much wider view projected by the EF lens.

An APS-C sensor would not see any difference between the image circles projected by the two lenses

[ebiggs1 · Accepted solution]

The simple answer is a 100mm is a 100mm and will always be a 100mm.  That is all you really need to know.  No matter what camera a lens is made for or intended to be used on it will remain a 100mm lens.  A crop sensor camera crops nothing. It is a misleading term.

[kvbarkley]

Yes, a 100mm is a 100 mm, but you also need to know the field of view for your camera so you know what to expect when you put it on the camera. Since an APS-C camera shows a portion of the Full-Frame FOV. Which is why we talk about "FF equivalent", 1.6X factors and crop-frames in the first place. In fact, that is exactly the problem the OP had.

[ebiggs1]

"...you also need to know the field of view for your camera so you know what to expect when you put it on the camera"

Of course this is true and important to know.  The term crop factor is not.  It is a misleading concept.  Just look at all the confusion it causes especially notable on the ole inner web. All cameras are full frame in the sense you get exactly what you see in your view finder. Full frame. That is all anyone really needs to understand.  People that didn't grow up with 35mm film couldn't care less. The term is ubiquitous in identifying the altered field of view caused by using smaller sensors in cameras compared to  35mm cameras.  Nobody generally uses the term on any other camera except for Rebels and certain other so-called crop cameras.  For instance the "crop factor" for a 645 is .62 but you rarely or ever hear it.  6 x 7 medium format cameras have a crop factor of .5 but have you ever heard it used? No, of course not. Hasselblad 500 series cameras have a .55 crop factor.  So what, they still give you exactly what you see in the view finder.

[TCampbell]

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@ebiggs1wrote:

The simple answer is a 100mm is a 100mm and will always be a 100mm.  That is all you really need to know.  No matter what camera a lens is made for or intended to be used on it will remain a 100mm lens.  A crop sensor camera crops nothing. It is a misleading term.

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A crop sensor camera does crop ... the sensor (hence the name "crop sensor").  See Wadizzle's image.  The OP has an APS-C crop-sensor camera... not a full-frame camera.  Using an EF vs. EF-S lens at the same focal length changes nothing for the OP.  But if the OP were to also own a full-frame sensor camera such as a 6D, 5D, or 1D X series and used an "EF 100mm" lens on the full frame camera and then used it on the crop-frame camera, there'd be a very noticeable difference caused by the crop.

The analogy I use is to imagine a movie "projector" and a movie "screen".  

Suppose you position a movie projector so that it projects your movie onto an 8' x 12' screen -- and it perfectly fills the screen.  (that would have a diagonal size of about 14.4 feet).  

Now suppose you don't touch the projector... but you remove the 8 x 12' screen and put a 5 x 7.5' screen in PRECISELY the same spot.  (that would have a diagonal size of about 9')

That screen is smaller than the 8 x 12' screen by a "crop factor" of 1.6.  

Since we did not touch the projector ... only the screen ... the projector is still projecting the same size image... but much of it is missing the screen and spilling onto the walls behind the screen.

This is exactly what happens with a crop-frame sensor camera.  An "EF" lens is designed to project an image circle (it's a circle because the lens is round... not rectangular ... and there's nothing in the lens to mask the size to a rectangular shape) which is large enough to completely fill a "full frame" camera sensor (a full frame sensor is about 24mm tall by 36mm wide).  When you use that same "full frame" (Canon EF series lens) on a camera that has an APS-C size "crop frame" sensor, the lens is projecting the identical image (just like the movie projector) but much of the image is spilling onto the walls of the camera ... and a smaller area is landing on the sensor.

A Canon EF-S lens is designed for use on APS-C "crop-frame" cameras and the only difference is that the image circle it projects is designed to be only large enough to fill the crop-frame sensor (if you tried to use the same lens on a full frame camera -- besides the fact that it wont fit -- what you'd find is that the corners of the image are completely black because the lens does not proejct a large enough image circle to completely fill the sensor.

It is a "crop sensor" because it is "as if" someone took a full frame sensor and physical cropped it down to a smaller size ... dividing it's dimensions by 1.6x.

Things get confusing when we print the images... If you want to print an image... let's say you want a nice big print to hang on the wall and you pick an 18 x 24" size.  When you print this with the full frame sensor you get an 18 x 24" image.  When you take the image from the crop-sensor camera, you STILL enlarge it to fill the 18 x 24" image (you just have to enlarge it more) but the crop frame camera only has the part of the image that would have been near the center of the full-frame version of the image.

The original point to the crop-factor sensor size was that physically large digital sensors were ludicrously expensive... but the smaller size was affordable so that's the format that became popular.  And since most DSLR cameras are crop-sensors... Canon realized they could further reduce the price by designing lenses specifically for the crop-sensor size.  Since these lenses only have to produce an image circle about 28mm across (vs. a full-frame lens which has to project an image circle at least 44mm across), the lens elements could all be smaller.   The lens would physically be smaller.  The lens would weigh less.    It would cost less to produce.  And the best part... it does not actually sacrifice image quality.

This allowed Canon to introduce DSLR cameras where the camera body + lens was at a price point that the masses could afford.

[kvbarkley]

I think ebiggs point is that why should 35mm film be considered the standard frame of reference? Why not make APS-C the standard and FF "extended frame"?

[TCampbell]

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@kvbarkleywrote:

I think ebiggs point is that why should 35mm film be considered the standard frame of reference? Why not make APS-C the standard and FF "extended frame"?

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I've wondering the same thing... there are some odd terms.  For example... a 6cm x 6cm film negative (or sensor size) is referred to as "medium format" even though that's quite a bit larger than "full frame".  

I can only imagine this came from the overwhelming popularity of the 35mm format.