, 7mm wide angle, for Canon EOS lenses, white, angled eyepiece

It does what it's supposed to do: serving as a viewfinder of an EF lens without a camera. I noticed some imperfections though. The internals of the assembly is not clean. This is usually undetectable until a small aperture lens is attached. Here I was using super-telephoto lenses (400mm+) with stacked teleconverters. The F number can be F/16 or lower. Then, I could see dust spots. Another issues is that the angled finder probably uses some angled mirrors inside. When used with a small aperture lens (again), a vertical line becomes visible through the center of the image. These are some annoyances hampering the observation a little. In general, it is a capable device.I found the longest focal length I could get was using an EF 400mm F/4 DO IS USM II. Longer lenses use the focus-by-wire mechanism and hence become unusable. I stacked two 2X extenders (Canon v3 and Tamron SP) resulting a 1600mm F/16 lens. Basically, the magnification (1600mm/7mm~=230X) allowed me to see the craters on the Moon.