Hi, Boris.
Images of point-light sources thru an optical system *with any kind of
obstruction* will degrade due to diffraction. When the obstruction comes
from an iris diaphragm (or the secondary mirror support on Newtonian
'scopes), you can see a number of rays related to the number of elements on
the diaphragm, but more often than not, the number of rays is *twice* the
number of elements -- IIRC, this happens with odd numbers (e.g. 5 blades
make 10 rays, 7 blades make 14 rays, etc).
But yes, there are (older) lenses with *a lot* of diaphragm blades -- I
have now in my hands a Jupiter-11 (Russian copy of the pre-war Z*iss Sonnar
135mm F4, in L*ica thread mount) and it seems to have 12 blades...
Diffraction may have a stunning effect. A 30 0iameter obstruction (like
those on mirror lenses) can reduce resolution by 50%!!!
All the best,
...
Carlos J. Santisteban
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