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A 40mm secondary used with a 200mm primary gives a secondary obstruction of 20%.
This is by no means excessive and I wouldnt bother reducing it unless the primary mirror is super sharp and you want to specialise in planetary observing with it. Advice I have had suggests you need perfect conditions and great optics to see any improvement by reducing the obstruction from 20%.
In my 10 inch f5, the secondary obstruction is 26% !
By having a smaller secondary you are throwing away fully illuminated field size, which matters for wide field observing, but not for planetary where the object is small.
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