Leica's Universal Wide Finder works great and adds a bubble level visible in any light through the finder.
The Leica Universal Wide FInder is the world's most precise 21mm finder, as well as the world's most precise 16mm, 18mm, 24mm and 28mm finder.
It is fixed-focal-length
It has frame lines for 16, 18, 21, 24 and 28mm lenses. Only one appears at a time...
Its magnification is fixed at 0.28x. Different finder lines appear as you change the settings.
The view is moderately polarized so that the bright lines work. Caution when viewing through polarizers or polarized subjects: For example: skies. They will look different through the finder compared to the true/final film result.
Viewing is optimum with your eye 1/2" (15mm) away. Get too close and the view is a little softer.
There is a glow-in-the-dark bubble level visible under the frame lines.
Dimensions: 2.0 x 2.8 x 1.5" (52x 70mm x 38mm) DWH, including the foot.