I recently purchased a Canon 6D....

[PhotosByNeva]

I wanted to upgrade from my Rebel. I have several lenses already and noticed that when I use them on my 6D there is a round black ring around the outside edges. Upon reading it seems that the Rebel has a "cropped frame" and the 6D has a "full frame". Does this mean that I have to get all new lenses to use with my 6D, and make sure they are EF?

[ScottyP]

Yes. I am surprized you were able to even mount an EF -s lens. Do not do that anymore as they are not meant to go together and in some cases you can damage the camera or the lens by doing so.  

You need lenses for full frame Canon cameras. Either Canon EF lenses or 3rd party lenses made for Canon full frame mounts.   The different manufacturers (Sigma, Tamron, etc) use different letters to designate FF vs. crop lenses.  

[Waddizzle]

I have found a way to cheat and mount an EF-S lens on a full frame body.  I used to use an extender and close-up filters on my Rebel as an inexpensive way to explore macro photos.  After I purchased a 6D, I noticed that the extender was EF mount, but the bayonet to mount a lens had both a red dot and a white one, just like my Rebel. 

Sure enough, with the extender attached, I could mount an EF-S lens without issue.  Of course, I could see the entire image circle.  But, I thought I was pretty clever just the same.

[PhotosByNeva]

I do have extenders that I bought to experiment with macro. I LOVE them! I have had so much fun exploring the tiny world in BIG pictures. Have you photographed an ants eyes before? lol
Maybe I could try that.
One thing, what is the significance of the red or white dot, because I did notice that one of my lenses has a white dot.

[ebiggs1]

"I have several lenses already ..."

Are any of these Canon brand lenses?  It is possible for the rear of the lens to strike the mirror.  It can be cracked if EF-S lenses are "modified" to fit on a 6D.  Sigma and Tamron lenses will bolt right up and will cause the black corners.

The "S" in EF-S stands for short focus.  That is why they have pin to make mounting impossible.

[PhotosByNeva]

I do have some Canon lenses. I just took the 35-50mm Canon lens that was on my original Rebel (actual 35mm film camera) and put it on my 6D. I took a couple pictures with it and it seems to be doing fine, no black edges.
Sigma DC 18-250 mm Macro HSM
Bower 35-500mm Fixed Focus Lens with Canon Adapter (I haven't tried this lens out yet on either camera)
Zeikos AF Macro Extension Tube Set (3 pc): I have used this but not with AF as they seem to work best with manual focus.

[RobertTheFat]

---

@PhotosByNeva wrote:
I do have some Canon lenses. I just took the 35-50mm Canon lens that was on my original Rebel (actual 35mm film camera) and put it on my 6D. I took a couple pictures with it and it seems to be doing fine, no black edges.

---

That's because a 35mm film camera incorporates the very definition of the term "full-frame". A full-frame digital camera is one whose sensor size is 36 x 24 mm, the frame size of almost all 35mm film cameras.

APS-C "cropped frame" lenses are an entirely different matter. Very few of them will fill the sensor of your 6D, and any that do will fall off in image quality near the edges. And all of them are potentially able to damage your camera. The APS-C spec allows the lens to extend farther into the camera, where it can interfere with the mirror or other parts of the mechanism. And even if a given lens appears to have enough clearance, it may extend farther back when it's zoomed or focused.

Buying the 6D may have been an expensive mistake, but you can make the best of it. The 6D is a very good camera that can serve you well for many years. Don't place it at risk by trying to use inappropriate lenses just because you happen to have them lying around.

[TCampbell]

Do these lenses screw on to the front of existing lenses?   Or do they mount directly to the camera body?

The 6D is indeed a full-frame sensor body and it requires Canon EOS "EF" lenses (without the "-S" suffix)   It can also use the EOS TS-E and MP-E specialty lenses.   You can use third party lenses if they are designed for use for Canon EOS full-frame bodies.

[PhotosByNeva]

They screw on to the camera body. I didn't do enough research before my upgrade because I have several lenses that fit my older DSLR Rebel and I guess I have to buy all new lenses for my 6D. I just paid over $600 for a new Tamron Piiezo Drive 16-300 mm lens that won't work on my Rebel. I get two shots and it shuts down my camera, same problem with the 20D I had. It works on my 6D just fine except it isn't a full frame lens apparently. 

[ebiggs1]

The specs clearly state, 

"Tamron Di-II lenses are engineered expressly for digital SLR cameras with image sensors commonly referred to as APS-C, measuring approximately 24mm x 16mm. Rendering an ideal image circle for APS-C sensors, Di-II lenses also include properties to optimize digital imaging performance."

So that is the problem with that lens.  Not all third party lenses are compatibile with all Canon cameras.  Even the ones that are designed to work on a FF and/or APS-C, may not work correctly.  Most newer versions do, however.  Sometimes, try before you buy is a good rule.  Plus third party lenses do not have the altered mount to prevent you from mounting the wrong lens as you have found out.  Without modification of the mount, you can not mount a Canon brand ef-s lens on a 6D.