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nobody

15 Mai 2014 02:16



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Avantajul unei oglinzi diagonale cu substrat de "fused quartz" ar fi doar la greutate, in sensul ca avand o rezistenta mai mare se poate face oglinda mai subtire si mai usoara pe formatul de 2". Dilatarea termica este nesminificativa.

Cat despre calitatea slefuirii, lucrurile sunt discutabile:

As noted before, the P-V error alone tells little about specific effect of the diagonal on image quality. For the same 1/4 P-V value, the Strehl degradation factor can be anywhere from 0.95 with spherical surface form (or even less with a local surface error), to 0.57 with surface roughness. With an excellent 0.95 Strehl primary, the former would result in a 0.90 optics Strehl, and the latter in decidedly substandard 0.54.

With star diagonals, converging cone uses much smaller portion of the optical surface. Thus, even much larger errors smoothly distributed over most of the surface have no appreciable effect on wavefront quality. However, local surface errors, especially in the mid-area, transmitting the light for the central portion of the field, can have significantly greater effect. Another difference is that star diagonal will scatter light for given small-scale surface roughness to much smaller radius than Newtonian diagonal, due to larger relative diameter of surface irregularities in the reflected wavefront.
http://www.telescope-optics.net/newtonian.htm

Totusi, parca nu as pune o diagonala l/1 pe un Takahashi.
Cat despre specificatiile chinezesti de "1/12 lambda surface quality", nu te astepta la mari minuni, mai ales pe un ED80 (tot chinezesc). Poti sa pui si diagonala de l/100, ca tot nu iese mai mult de l/4.