Archived posting to the Leica Users Group, 1997/01/12
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]At 10:33 AM 1/12/97 -0400, Fred Ward wrote: >2. We have truth in advertising laws here, and Questar was then >advertising f/stops. What was advertised and what was printed was not >so. Fred, this is an issue with ALL mirror-lenses and with a lot of conventional designs, as well. The f/stop is a mathematical calculation -- Questar did nothing dishonest by advertising the scope as an f/14. It's just that the useful number for a photographer is the t-ratio. Those of us who use a lot of mirror lenses generally are experienced enough to ask the right questions and to evaluate the answers appropriately. Incidentally, this same issue arises with every manufacturer of cat lenses, from Asahi to Zeiss -- yet ALL list their wares by f/stop, even though the lenses are a bit slower. Test a Canon or Nikon mirror-lens and you'll find the same situation exists. The only exception to this was Kilfitt/Zoomar, and they were forced by market pressures to revert to using f/stops in their literature, as pro photographers at the time accused THEM of 'fraud' by not using the same standard others used. Nonetheless, Kilfitt continued to list the T-stops in their spec tables. Marc msmall@roanoke.infi.net FAX: +540/343-7315 Cha robh bas fir gun ghras fir!