Optical colors don't just include RGB. In optics yellow and purple are also primary colors. The visible band of 400-700nm is divided into more than 3 color bands because optically they have to be treated differently. Kent Gittings
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Martin Trucco Sent: Wednesday, November 21, 2001 8:01 PM To: [EMAIL PROTECTED] Subject: Re: APO Lenses. >Now this I'd like to hear more about. Can you elaborate on this point, specifically, how do manufacturers get away with labeling a lens as Apochromatic when it isn't? Is the term "APO" used to imply that a lens is apochromatic, when, in fact, it's just a model name given to the lens? Which lenses that are designated as "APO" lenses are not, in fact, apochromatic? Which are? Just a few examples would be appreciated. > >Would a lens have to be designated as "apochromatic" to be apochromatic, as opposed to being labeled as "APO", which may not be apochromatic? Apochromatic lenses (as microscopes, for example) are supposed to focus the three main light rays (blue, green and red) at the same point; opposed to achromatic lenses that focus two of them and the third very near. I don't remember where I've read this (maybe from Bob Atkins) but APO doesn't always mean "apochromatic" (the same as a car named 1125 TDX doesn't need to be turbo diesel, it is just the name and the company is deciding to "mislead" your attention by labeling it that way), and some lenses are "more" apochromatic than others. Maybe a 70-210 brand A is always apochromatic and a 70-210 brand B is apochromatic at 135 and focused at 3m. Unfortunately I don't have a list of true apochromatic lenses, this is something I've read. BTW: At least theoretically you can design a bad quality apochromatic lens (that focuses the three ... but quite softly) and a very good achromatic one (that focuses very sharply two of the three main colors and the other very near). HTH Martin www.martintrucco.com.ar - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ********************************************************************** - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
