Inside Look at Canon’s EF Extenders (Canon DLC)

The Canon Digital Learning Center published part 2 of their article series about Canon EF and tele extenders (part 1 is here). Some extender basics from part 1:

• Tele extenders cause an unavoidable loss in light transmission to the imaging sensor or film. There’s a constant, steady 1-stop light loss with 1.4x Extenders and a 2-stop loss with a 2x. This is consistent, regardless of camera or lens brand.
• A 1.4x Extender multiplies the effective lens focal length by 1.4x. Thus, a 300mm lens would have the power and field of view of a 420mm lens. And a 2x Extender doubles the effective lens focal length.
• When using a digital SLR with an image sensor smaller than a full-frame, it’s “crop factor” is added to whatever an extender is to calculate effective lens coverage relative to a full-frame camera. In other words: an EOS Rebel has a 1.6x crop factor. If using a 200mm lens with a 2x Extender (400mm equivalent), putting it on an EOS Rebel would result in a lens that effectively “acts” like a 640mm lens (400mm x 1.6 = 640mm) would on a full-frame or 35mm film camera.
• Tele extenders do not impact or change a lens’ minimum focus distance. Because extenders do impact effective focal length, at minimum focus distance, a lens with extender provides a noticeably tighter composition of small objects than the lens alone would.
• Canon EF 1.4x and 2x Extenders are exclusively designed to work with specific, compatible Canon EF lenses. Part of the reason for this is the front element design of Canon extenders, which literally projects forward and into the rear of any lens they’re attached to. This enhances optical performance with those lenses, but prevents their attachment to many lenses that have a rear element flush with the rear lens mount.
• Canon EF lenses that are extender-compatible:
  • All fixed focal length EF L-series telephoto lenses, 135mm and above (thru 800mm)
  • All white-colored EF 70-200mm f/2.8 and f/4 L-series zoom lenses (all versions)
  • EF 100–400mm f/4.5–5.6L IS USM zoom
  • EF 200–400mm f/4L IS USM Extender 1.4x zoom (can be used in addition to lens’ built-in 1.4x)