Maximum aperture at 1:1 macro

Started 5 months ago | Questions thread
OP WFulton Senior Member • Posts: 2,697
Re: Maximum aperture at 1:1 macro

rubank wrote:

Here you can get all the info you want:
http://www.pierretoscani.com/focale.html

Scroll to almost bottom of the page to see the 105/2,8 VR, but don´t forget to view all the rest

Wow! Thank you.  It's going to require some study, but it certainly all seems to be there. One spot even says:

Note 1:

At reduced focusing distances, the front elements of this lens tend to limit the diameter of the incident beam, causing it to lose contact with the aperture diaphragm. When g = -1, the opening number imposed by these front elements is N = 4.5 (see Fig. 36-2). In order for the diaphragm to retain its functions, a mechanism slightly tightens its opening until the effective opening number Neff = 4.80.

I know short lenses can do 1:1 with less extension, but I'm still struggling with the focal length decreasing.  

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