The built-in dioptric adjustment (in the form of a dioptric adjustment knob right next to the viewfinder — see page 34 of the Canon 7D Manual) on the Canon 7D offers a diopter strength adjustment range from -3.0 to +1.0 m-1.
If this adjustment range is insufficient for your needs, you will need to purchase the appropriate Canon Dioptric Adjustment Lens Eg (at the time of writing, Adorama has the bigger collection of the Eg range of Canon diopter lens eyepieces.)
“apersson850” has the following comments in a forum discussion on DPReview:
Since I’ve actually bought a correction lens for my 7D, you can now trust that I know exactly how this works.
First, the correction lens is indeed one single piece. Lens, holder and rubber, all in one.
Third, probably due to the fact that everybody knows that the previous designs are easy to loose, these new ones have a design with release buttons and hooks, to keep them on the camera. If you don’t press the buttons, you almost need a crowbar to remove them from the camera.
Fourth, the rubber part is thick and seems well attached. I doubt you’ll wear it out in any short time.
I can use my camera with glasses and the normal viewfinder, but am just outside the adjustment range without glasses. With a correction lens, I move the adjustment range so I can still use it with glasses, just with the internal setting set differently, and then without glasses, just by adjusting the diopter setting in the camera. Thus the correction lens stays on the camera, no matter what I do, so I don’t lose it.
“HowardBerger” shares a response from Chuck Westfall:
It’s true that rubber frames are built into the Eg-series dioptric correction lenses. You can still use the E-series dioptric correction lenses which cost less, but Canon does not offer rubber frames separately for cameras that use Eg-series viewfinder accessories.
Angle Finder C is fully compatible with all EOS bodies including those that use Eg-series viewfinder accessories.
Thanks for the kind words, and Happy Holidays!
Advisor, Technical Information
CIG Professional Prods Mktg Division
Canon U.S.A., Inc.
Canon 7D – Main page.