What imakes a scope an APO?

opticsplanet.com · Posted: Mon Jun 20, 2005 8:09 am Post subject:

Not necessarily, since there are different grades of ED/fluorite. Some
manufacturers use crystals of fluorite embedded in the glass, other full
fluorite crystal, still others use various grades of ED.

Focal length is another consideration. The longer the focal length, the less
the chromatic abberation you will likely have. Conversely, the shorter the
focal length, the more difficult true APO performance is to achieve. ED and
APO are the hot "buzz" words today, but it takes more than just slapping an ED element or adding a third element to get true APO performance. Nor is a clam of ED or APO any guarantee of other optical parameters. A poorly ground lens is a poor performer no matter what it is made of. The degree to which a scope eliminates chromatic abberation is the only true test of APO performance.

Haven't had a chance to test the RA-88-SA. but if they are claiming "semi"
APO, at least they are being honest. It tells me to expect a reasonable
degree of color correction, but not to expect it to compare to a Televue or
Astrophysics in this regard. Believe me, I have seen many inexpensive scopes that claimed "ED" with as much chromatic abberation as a standard achromat.

All in all, we have recieved excellent feedback on the Apogee binoscopes.
Good products at a reasonable price.
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