compare
Tamron was built in Schmidt-Cassegrain designs differrence from most Russian lens which area Maksutov design
They are both in the same market share. 3M-5CA stand for latest russian Msksutov mirroe and Tamron stand for latest series of 500mm mirror too. Tamron seem to be brighter than 3M-5CA at the same speed. and got lil bit feature that can take close up at 1.70 m while 3M-5CA at 4.00 m. but The price are higher too Tamron ~ 250-300$ 3M-5CA ~ 150-200$ ( with out shipping)
weigh Tamron [0.595 kg] 3M-5CA [0.620 kg]
SIZE Tamron [87 x 91.5 mm] 3M-5CA [ 83 x 139 mm]
FILTER Tamron[ 82 mm] 3M-5CA [ 72mm]
Min focusing range : Tamron[1.70 m ] 3M-5CA [4.00m ]
for futher detail on each lens
http://photoprop.blogspot.com/2009/06/tamron-sp-500-f8.html
http://photoprop.blogspot.com/2009/06/zm-5sa-3m-5ca-mirror-lens.html
compare size
compare photo at infinity
.compare sharp ness
(Schmidt -Cassegrain) was invented by Bernhard Schmide in 1930 by using Primary mirror in Spherical type and using lens called "Corrector Plate" in aspheric element for Primary Mir ror
(Maksutov Cassegrain) was invented by Dmitri Maksutov in 1941.there aren't much different from Schmidt-Cassegrain, just a Corrector Plate was in deeply curved spherical meniscus lens which made the Maksutov limitation ,hard to make in big size. and that make msksutov limit size at 7" or perhaps hard to build bigger than this.
picture from http://www.darasart.com/telescope/catadioptric.htm
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