Newtonian obstruction

[N3ptune]

Hello, I have this question today.. my telescope is BKP 200 DS 200x1000 and I am not sure about the obstruction % of it. I saw 25% obstruction on a spec sheet but my rudimentary area calculations tells me the secondary is about 8% obstruction for the primary mirror. Secondary is about 57mm wide @ 45 degrees. So I figure a 57mm diameter circle obstruction over a 200mm primary mirror plus a few mm² for the spiders (not included in the+- 8%)

Secondary at 45d: 57mm wide: 2551.75 mm²

Primary : 200mm wide: 31415.92 mm² (25% of that is 7853 mm²)

Does anyone know what is the right % obstruction for that telescope?

Thanks.

[Ricochet]

The obstruction is given as a comparison of diameters not the percentage area that is blocked so just 57/200. 

[N3ptune]

@Ricochet

Ah ok ok then that settles it at +- 28.5% obstructed. Thanks Ricochet.

[Louis D]

The reason it's calculated by diameter is that obstruction diameter determines the contrast of the telescope.  As the central obstruction gets larger, more and more light gets thrown into the out rings of the airy disk decreasing contrast.  The percentage of light lost is calculated by area of obstruction.