Lenses for full frame vs aps-c cameras.

[filmalaska]

101 question here- how does one differentiate the lenses between the full frame sensor cameras and the others? I come from the cinematography side, picked up a 6D for starters and am trying to figure out what the lens options are. Thanks

[RobertTheFat]

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@mdougc wrote:

But why, in my described test of the EF and EFS lenses with a APS-C sensor, did I get the identical picture???

There was NO CROPPING to be seen.

Something is missing in this stream of logic.

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Because on an APS-C camera, there's no effective difference between an EF lens and an EF-S lens. The only difference between the two lens types is that an EF lens is capable of filling the sensor of a full-frame camera and an EF-S lens isn't. If you used your EF lens on a FF camera, you'd see more of the scene because the sensor is larger. The APS-C camera wastes (i.e., "crops out") that extra area of the projected image because its sensor isn't large enough to accommodate it. With an EF-S lens, that extra area just isn't there. (And on an APS-C camera, you couldn't use it if it were.)

One reason people get confused like you are is that they try to interpret the charts that give "full-frame equivalent" focal lengths for the focal lengths of APS-C lenses. Ignore those. All you need to do is get used to the idea that a lens of a given focal range is more of a telephoto, and less of a wide-angle, on an APS-C camera than it would be on a FF camera. The fact that a given lens may or may not actually be usable on a FF camera is irrelevant to that understanding.

[Waddizzle]

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@mdougc wrote:

But why, in my described test of the EF and EFS lenses with a APS-C sensor, did I get the identical picture???

There was NO CROPPING to be seen.

Something is missing in this stream of logic.

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Actually, if you used the same camera body for all of your "tests", then you did see cropping, or a smaller angle of view.  Optically, the difference between an EF and EF-S lens is the size of the image circle that the lens projects on the sensor.

What your test may have proved is that the lens mounting doesn't make any difference, neither does the focal length.

[mdougc]

Accoding to this diagram, the EF 50mm lens with the APS-C sensor, should produce a photo that looks like a EFS 80mm lens was used,  It implies that the crop sensor causes an 1.6X optical zoom effect on the image projected by the "full circle" lens.

In face, when I read reviews of the Canon EF 24-105mm f/4 L IS USM Lens, it expliciely says that this lens, if mounted on a APS-C camera, will produce photos as if the lens was a 38-168mm lens.  And that is not true. It will act like a 24-105mm lens.

Optically, the explanation must be that the APS-C sensor must be designed to be closer to the lens - in fact, closer by a factor of 0.625 (the reciprocal of 1.6).  Otherwise, I would see an optical zoom effect.

As my test showed, a EF 50mm lens and a EFS 50mm lens produce the same image on a APS-C sensor.  There is a big difference is quality, sure, but it is the same image.

[MichaelGClark]

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@mdougc wrote:

Accoding (sic) to this diagram, the EF 50mm lens with the APS-C sensor, should produce a photo that looks like a (sic) EFS 80mm lens was used (no) it will look like an EF 80mm lens was used on a full frame 35mm camera,  It implies that the crop sensor causes an (sic) 1.6X optical zoom effect on the image projected by the "full circle" lens. The crop sensor does not cause any zoom effect from a FF or APS-C lens. Magnifying the image projected onto a 22.5x15mm sensor to the same disaply size as the image projected onto a 36x24mm sensor is what causes the additional enlargement. That is why you get the exact same enlargment from an EF-S lens set to 50mm as you do from an EF 50mm lens. It is also enlarged by the same factor to make the 22.5x15mm image projected onto your APS-C sensor a specific display size.

You're wishfully misreading it to say that a FF lens on an APS-C camera somehow causes the same lens to bend light differently as it passes through the lens. The full frame sized 44mm wide image circle of a 50mm lens includes the exact same part of the scene inside the 27mm wide center portion of the image circle that is the size of the image circle projectred by an APS-C lens as the APS-C lens does. It just includes a wider view of the scene outside that smaller 27mm image circle.

The larger image circle of the 50mm FF lens does not "stretch" the same angle of view as the smaller APS-C lens projects onto a larger image circle. To do that it would need to be an actual 80mm lens. The larger image circle contains a wider view of the scene, which your smaller sensor crops to the same angle of view as the angle of view APS-C lens provides.

In face (sic) , when I read reviews of the Canon EF 24-105mm f/4 L IS USM Lens, it expliciely (sic) says that this lens, if mounted on a APS-C camera, will produce photos as if the lens was (sic) a 38-168mm lens mounted on a FF 35mm camera.  And that is not true. It is true if you understand that the comparison is to a 38-168mm lens mounted on a FF 36mm camera. It will act like a 24-105mm lens. Yes! The lens projects the same image circle regardless of what is behind it. But your smaller sensor only captures a smaller portion of the image projected by the lens. To display that smaller 22.5x15mm image at the same size as an image captured by a 36x24mm FF sensor the smaller image must be enlarged by a factor of 1.6X more compared to the image from the FF sensor. If you enlarged both images by the same factor then the image from a FF sensor would be viewed 1.6X larger than the image from the APS-C camera. If you then trimmed the middle of the larger FF image to be the same size as the smaller APS-C image they would both show the same angle of view at the same display size.

Optically, the explanation must be that the APS-C sensor must be designed to be closer to the lens - in fact, closer by a factor of 0.625 (the reciprocal of 1.6).  Otherwise, I would see an optical zoom effect. What you are totally missing is that your APS-C sensor is smaller than a FF sensor. It sits the exact same 44mm from the lens flange as the FF sesnors in EOS cameras do. But it only records the middle 0.625 (linear measurement) of the view recorded by the 1.6X larger FF camera.

As my test showed, a (sic) EF 50mm lens and a (sic) EFS 50mm lens produce the same image on a (sic) APS-C sensor.  There is a big difference is (sic) quality, sure, but it is the same image. Of course they do. They're the same focal length!

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[isidroco]

Because you're not doing the test right. You should put the same lens in two different cameras, one FF and the other APS-C. You'll see that the picture in FF is wider. "1.6 equivalent" means that image produced in APS-C sensor will look like a 80mm lens (in your example) on an old film camera or a FF camera.
People used to film cameras find useful the equivalence, a regular lens there was a 50mm and now you have to put a 30mm instead to achieve the same framing as before.

[mdougc]

My test is wrong?

I wanted to see the diffence in images that an EF 50mm lens and an EFS 50mm lens would pruduce using an APS-C sensor.

I found that they are the same.

Using your suggested test procedure would be like I want to see how a large pair of pants fits me, so I ask my obese friend to try them on.

[RobertTheFat]

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@mdougc wrote:

My test is wrong?

I wanted to see the diffence in images that an EF 50mm lens and an EFS 50mm lens would pruduce using an APS-C sensor.

I found that they are the same.

Using your suggested test procedure would be like I want to see how a large pair of pants fits me, so I ask my obese friend to try them on.

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Let's review. We've given you three or four accurate explanations of what you're seeing, and you still don't get it. Go back and read them a few more times, and let go of your preconceived notions. There is no - repeat, NO - difference between what an EF 50mm lens and an EF-S 50mm lens will produce on an APS-C camera. The difference is entirely in what a 50mm lens will produce on a FF camera vs what it will produce on an APS-C camera. The only difference between an EF lens and an EF-S lens is that the former is designed to work on a FF camera and the latter isn't. If this explanation doesn't work for you, and you're not willing to accept that it's correct and move on, you need to find some books on optics and on how cameras work and delve in more deeply. Let me be clear: it's a GOOD thing that you want to understand the underlying physics. But this is not quantum chromodynamics or some other esoteric theory for which the jury is still out. If you read the relevant literature with an open mind, you will eventually see that what you're being told - and, let's face it, what you're telling us you're seeing - is correct.

[MichaelGClark]

"I get the same picture - same FOV, identical crop."

That's becasue they are BOTH 50mm lenses.

Compared to a 50mm lens used on a FF camera BOTH are cropped by your APS-C 70D.

The angle of view you get with BOTH 50mm lenses on your APS-C 70D is the same angle of view you would get with an 80mm lens on a FULL FRAME camera with a 36x24mm sensor.

"But why, in my described test of the EF and EFS lenses with a APS-C sensor, did I get the identical picture???

There was NO CROPPING to be seen."

Yes there was. BOTH images projected by both 50mm lenses were cropped equally by the same amount because the size of your camera's sensor was the same for both images.

[mdougc]

The reason I started this post:

I have a Canon EFS 18-55mm lens, and I really like the zoom range.  Of 4 lenses, it is my always-attached lens.

But I want a lens for higher quality, with zoom capability in that range.  90% of my photos are in the 20-40mm range.

So, I have looked at two lenses -

Canon EF 24-105mm f/4 L

Canon EF 17-40mm f/4 L

However, if these make images on my 70D as if they are 38-168mm and 27-64mm, respectively, then they are not good for my needs.  My test shows that these will perform in the specified range om my APS-C camera.  And that seems to contradict explanations that I see here and other places.

Regardless, does anybody out there suggest a high quality lens that zooms somewhere around 18-55mm???

By the way, Wikipedia says that Canon does, in fact, place the APS-C sensor closer to the lens than it does with the FF sensor.

It is the reason that they design the EFS mount so that it will not fit on a FF camera - it might damage the mirror.

[MichaelGClark]

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@mdougc wrote:

The reason I started this post:

I have a Canon EFS 18-55mm lens, and I really like the zoom range.  Of 4 lenses, it is my always-attached lens.

But I want a lens for higher quality, with zoom capability in that range.  90% of my photos are in the 20-40mm range.

So, I have looked at two lenses -

Canon EF 24-105mm f/4 L

Canon EF 17-40mm f/4 L

However, if these make images on my 70D as if they are 38-168mm and 27-64mm (they won't), respectively, then they are not good for my needs.  My test shows that these will perform in the specified range om my APS-C camera.  And that seems to contradict explanations that I see here and other places.

Regardless, does anybody out there suggest a high quality lens that zooms somewhere around 18-55mm???

EF-S 17-55mm f/2.8 USM or Tamron SP 17-50mm f/2.8 Di II.

I own both the Tamron SP 17-50mm and the EF 17-40mm f/4 L. On my crop bodies the Tamron is just as sharp and one stop faster than the EF 17-40mm is. The "L" lens does have better buiild quality and weather resistance. On my FF bodies the 17-40mm gives a much wider angle of view than either lens does on a crop body. The Tamron will actually mount on my FF bodies but the image circle does not cover all of the sensor. Even though it is an APS-C only lens (that's what Di II means in Tamron model names), none of the lens' elements protrude out the rear of the lens at any focal length or focus distance setting so there are no mirror clearance issues with that lens.

This is an image created by using the APS-C "only" Tamron SP 17-50mm f/2.8 Di II set at 17mm when mounted on a full frame Canon 5D mark II. The white rectangle is the part of the image that would have been captured by an APS-C camera.

The APS-C sized area enlarged by (roughly) the same magnification:

The APS-C area magnified to the same display size as the FF image:

The size difference of the objects in the scene is not due to the properties of the lens - it is the same exact picture (thus taken with the same lens at the same focal length).  The difference is because of how much more (1.6X) we enlarged it to view it at the same display size as the first image from above. 
 

By the way, Wikipedia says that Canon does, in fact, place the APS-C sensor closer to the lens than it does with the FF sensor. No it doesn't. Lens elements on the rear of an EF-S lens *may* protrude further into the mirror box (but it doesn't have to) at certain focal length and focus settings than rear elements of EF lenses. The registration distance (flange focal distance) is the same. But lenses such as the EF-S 10-22mm allow lens elements to protrude past the mounting flange and further into the front of the mirror box inside the camera than wide angle EF lenses are allowed to protrude.

It is the reason that they design the EFS mount so that it will not fit on a FF camera - it might damage the mirror. If the registration distance was shorter for an EF-S lens than for an EF lens, then mounting an EF-S lens on a FF camera would put the lens further away from the sensor than that same lens would be on an APS-C camera, not closer. You wouldn't have any issue with mirror clearance, but you would lose the ability to focus at longer distances, just like with an extension tube.

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