Bounced to me. ------- Start of forwarded message ------- Sender: [EMAIL PROTECTED] Subject: re: 105mm macro On Wed, 24 Feb 1999 18:48:41 -0500 [EMAIL PROTECTED] (Thom Hogan) wrote: >> the 105 micro Nikkor loses 2 stops of light at 1:1, becoming a 105/5.6. > >We need to put an end to the assumption that Micro-Nikkors maintain their >focal length when extended to 1:1. From my upcoming Nikon Lens Guide (Field >Guide, Flash Guide, Lens Guide, when will he stop?): Yes, I guess that if I wanted to be perfectly accurate I would have said it becomes a 74/5.0 lens, and it does not quite lose 2 stops at 1:1 because some focal length has been lost. And I should say that the f/stop is F/2.5 but the t/stop is T/5.0. (actually, if the focal length at 1:1 is 74mm, the lens is really F/2.35 and T/4.7). >At 1:1 focal length is approximately 74mm > >For the 60mm, at 1:1, the true focal length is about 49mm. >For the 200mm, at 1:1, the true focal length is about 102mm. > >> The 200/4, however does not lose any light, due to its IF construction, >and remains an f/4 lens at 1:1 > >Sorry, but due to the extension involved, it loses slightly over a stop of >light at 1:1 (Moose says 1 1/3 stops). This deosn't make much sense to me. At 1:1 the 200/4 is anly 102mm. But the diaphragm still has a size of 200/4, or 50mm. 102/50 gives you a f/stop of F/2. But you are focussed at 1:1, so you lose 2 stops of light, so you have a t/stop of T/4. Thus you should have a 104/4 at 1:1. Can anyone explain this to me? Maybe Moose was referring to the MF version? ------- End of forwarded message -------
