No, not the omnipotent "Q" from Star Trek... please read on...
Ok, no one seems to like the terms "semi-APO", "neoachromat". I realize that we've discussed the use of these terms. But I'd like to present a hypothetical scenario and perhaps define "quasi-APO". And please, no semi-pregnant argument ;-) that I think have not been
discussed (or had been discussed before my time ;-). This discussion is limited to visual use.
Let's start from some dim and mystic past discussions and let's use my favorite 4-inch aperture as example. I recall someone said that chromatic aberrations (CA) is:
CA(4-inch f/20 achromat doublet) = CA(4-inch f/8 APO doublet)
If f/20 is incorrect, please supply a correct number. But it doesn't matter in this discussion. First everyone would agree that an 4" f/5 achromat is quite colorful compared to the 4" f/10 achromat (eg. Synta). And I would assume that the 4" f/10 achromat would be more "colorful" than an f/20 achromat. If you agree with this, then I assert that there exists a zone of **perceived** color correction that "looks" better than f/5 but not good enough like an f/20. Why then can't "quasi-APO" (Q-APO ;-) be used to describe a refractor that falls in-between the equation above? Also, Ed Ting, Todd Gross and other experienced reviewers have mentioned this "property" (of semi-APO) in more than one of their reviews.
I don't know if optical theory allow for this "twilight zone".
Thanks,
Ron B[ee]
Ok, no one seems to like the terms "semi-APO", "neoachromat". I realize that we've discussed the use of these terms. But I'd like to present a hypothetical scenario and perhaps define "quasi-APO". And please, no semi-pregnant argument ;-) that I think have not been
discussed (or had been discussed before my time ;-). This discussion is limited to visual use.
Let's start from some dim and mystic past discussions and let's use my favorite 4-inch aperture as example. I recall someone said that chromatic aberrations (CA) is:
CA(4-inch f/20 achromat doublet) = CA(4-inch f/8 APO doublet)
If f/20 is incorrect, please supply a correct number. But it doesn't matter in this discussion. First everyone would agree that an 4" f/5 achromat is quite colorful compared to the 4" f/10 achromat (eg. Synta). And I would assume that the 4" f/10 achromat would be more "colorful" than an f/20 achromat. If you agree with this, then I assert that there exists a zone of **perceived** color correction that "looks" better than f/5 but not good enough like an f/20. Why then can't "quasi-APO" (Q-APO ;-) be used to describe a refractor that falls in-between the equation above? Also, Ed Ting, Todd Gross and other experienced reviewers have mentioned this "property" (of semi-APO) in more than one of their reviews.
I don't know if optical theory allow for this "twilight zone".
Thanks,
Ron B[ee]
