my eqpt r d70, kit len n sigma 18-125.

tink of getting a nikon 5t close-up filter, but based on the calculation for magnifying,
m = f/(1000/d) and d = 1.5

my sigma len give me 0.187x or 0.28x (nt sure shld use 125 or 187 in the calculation )

1: my calculation/understanding correct?
2: worthwhile to buy the filter, since magnify not much?
3. the sigma min. focusing distance is 0.5m at 125mm. using the cu filter seem dat min focus distance now is 666mm. worst off?

all advice or comments welcome. thanks in advance.