Nothing to do with coatings. You can make an Aspherical plastic coating to control non-chromatic aberrations but the only thing that can control chromatic aberrations or color fringing is the dispersion value of the glass. No coating you can put on a lens can affect the dispersion only the transmission and reflectance. Plastic lenses that are used in cheap little consumer applications have very little dispersion control. Currently only elements made of either glass or naturally/artificially grown crystals of calcium fluorite or quartz can affect the chromatism of an optical system. Kent Gittings
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]On Behalf Of Rob Brigham Sent: Thursday, November 22, 2001 6:39 AM To: [EMAIL PROTECTED] Subject: RE: APO Lenses (was Re: Layers, Sharp Focus, and New-FangledColor Film) I think you are confusing this with 'Aspherical' - shape of lenses to correct aberrations. The Sigma APO refers to a lens coating rather than lens design. > -----Original Message----- > From: Lon Williamson [mailto:[EMAIL PROTECTED]] > Sent: 22 November 2001 11:30 > To: [EMAIL PROTECTED] > Subject: Re: APO Lenses (was Re: Layers, Sharp Focus, and > New-FangledColor Film) > > > Bob Walkden wrote: > > > > Hi, > > > > it's my understanding that there is no (inter)national standard (eg > > ISO, ANSI, BSi, DIN etc.) definition of the word > 'apochromatic', therefore > > the lens manufacturers can do some humpty-dumptying and > make the word mean > > whatever they want it to mean. > > Maybe not. As I understand it, APO elements, like any other element, > may be a) plastic, b) molded glass, or c) ground glass, with cost > escalating from a (cheapest) to c (pricey). > > So, I'd bet that my 70-300 Sigma APO Macro, for example, uses solution > A. > > -Lon > - > 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 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 .
