Update: The MP-20 was tested against 10 other lenses at 5x on Closeuphotography.com: https://www.closeuphotography.com/5x-lens-test
Over the years I’ve owned 5 or 6 of these lenses and they have always been one of my favorites, good sharpness across a big field and good chromatic aberration control. The compact barrel and rounded nose makes this lens very easy to use compared to a big bulky lens like the Canon MP-E 65. This is an easy lens to recommend for the 3-5x range and its hard to wrong with one.
Its hard to beat the MP-20 and its brother the MP-35 in fact the sharpness and CA correction is actually better than the MP-E 65 for about 1/3 to a 1/4. Other lenses in the same category are the Minolta Micro-Rokkor minolta 12.5mm and 25mm lenses, for example, have unbelievably bad chromatic aberrations compared the Canon MP-20 and cost a lot more on the used market. The Olympus Zuiko 20mm and 38mm are expensive on the used market and have no image quality advantage and come with a lens mount that’s difficult to adapt.
These lenses were sold starting in the the late 1970s so almost every copy will have dust inside the lens but it seems to have zero effect on image quality so its not something to worry about. Its hard to believe but these lenses sold for about $85 in the 80s which is equivalent to $200 in todays dollars, thats still an excellent deal.
RATING
What I Like:
Sharpness
Big image circle
Low cost
CA correction
RMS mount
Compact profile
What I Don’t Like:
5 blade iris aperture shape
TECHNICAL DETAILS
Canon 20mm f/3.5 Macrophoto Lens
Lens Type: Bellows lens
Filter threads: None
Mount: RMS. This lens is very easy to mount with adapters.
Current Retail Price: Discontinued
Typical used price: $100-300, sometimes prices can spike higher.
Iris: 5 blades
Recommended Magnification range: 3-5x
Coverage: Full frame
Forward or Reverse Mount: forward
Lens Construction (group)3Lens Construction (element)4No. of Diaphragm Blades6
LINKS FOR MORE INFORMATION
Macrophoto 20mm lens on the Canon global site:
https://global.canon/en/c-museum/product/sp8.html
Canon Canon FD Resources site:
http://www.mir.com.my/rb/photography/companies/canon/fdresources/fdlenses/fdmacro/2035macro.htm