Catalyzes the dehydrogenation of methylene-H(4)MPT. Can also catalyze the reversible dehydrogenation of methylene-H(4)F with 20-fold lower catalytic efficiency. 5,10-methylenetetrahydromethanopterin + NADP(+) = 5,10-methenyl-5,6,7,8-tetrahydromethanopterin + NADPH (6R)-5,10-methylene-5,6,7,8-tetrahydrofolate + NADP(+) = 5,10-methenyltetrahydrofolate + NADPH Optimum pH is 6.0. Optimum temperature is 45 degrees Celsius. One-carbon metabolism; formaldehyde degradation; formate from formaldehyde (H(4)MPT route): step 2/5. Homotrimer.