I read that in a 90 degrees prism diagonal. Chromatic aberrations
are almost cancelled. I'd like to know to what extend it is true
and what is the rule. For the entering light cone, it encounters
flat surface via the air-glass interface, and since there is an angle
of the incident light, chromatic deviation occurs from the splitting
of the white light into the different wavelength inside the glass, But
when the light cone exits on the other flat surface of the prism diagonal,
the chromatic aberrations are cancelled from the opposite
glass-to-air interface and the light cone returns to its original
unchromatic aberrated form (this is assuming of course that the
objective lens of the telescope is an apo or sct where chromatic
aberrations are a nil compared to an achromat).

Now what is the rule, like does shorter focal ratio or steeper
light cone make the prism diagonal ineffective in cancelling
the chromatic aberrations inside the prism diagonal? In long focal
ratio scope or light cone entering and exiting a prism diagonal with
parallel entry and exit surface (remembering that there is no chromatic
aberrations from the internal reflections). How many percentage
approximately of the light cone returns to its original unchromatic
aberrated form after it exits the prism diagonal.

If anyone has any site or articles about this in details. Let me
know. Thanks. (Note: Some may say that a prism diagonal is
obsolete and just buy a mirror diagonal. Well, the above inquiry is
to understand better the behavior of chromatic aberrations in
parallel entering and exiting surfaces such as a prism diagonal
and novelty item like binoviewer (which has almost zero
chromatic aberration when I observe thru one) and also to
get some idea like how some products such as the chromacorr
(which removes spherical aberrations) work.

optidud