D700 - 105mm micro aperture problem

[goldenstar]

Hi,

Got my 105mm f2.8 micro lens through today. Problem is I cant select f2.8, it will only go to f3.5 in aperture mode.

Am I missing a setting, or is it possible the lens is goosed.

 

[goldenstar]

ignore me I'm being a ****!

 

[HoppyUK]

I think the way Nikon report f/numbers is different to Canon.

Canon sticks with the f/number, which is theoretical and doesn't change with a macro/micro lens, but the 'effective aperture' does as you focus very close and at 1:1 while the f/number is still technically f/2.8, the effective aperture is two stops less than that, ie f/5.6 due to the magnification (inverse square law).

In this situation, I think I'm right in saying a Nikon lens will report f/5.6 and the Canon f/2.8, even though they are both correct in different ways and the light coming through the lens is identical.

 

[puddleduck]

Nikon macros lens report f/2.8 at infinity, and as you focus closer you lose light.

The 105mm VR doesn't go right up to f/5.6 from memory but not far off.

Tamron (in Nikon fit at least) does the same.

Doesn't really make any difference - in both cases the aperture blades are at the f/2.8 position, but effective aperture is reported differently. So you still get f/2.8 bokeh, even if effective aperture is say.. f/4.5.

 

[HoppyUK]

Nikon macros lens report f/2.8 at infinity, and as you focus closer you lose light.

The 105mm VR doesn't go right up to f/5.6 from memory but not far off.

Tamron (in Nikon fit at least) does the same.

Doesn't really make any difference - in both cases the aperture blades are at the f/2.8 position, but effective aperture is reported differently. So you still get f/2.8 bokeh, even if effective aperture is say.. f/4.5.

I think that's right Andy. From memory of another debate, I think what happens is that the actual focal length reduces with internal focusing so at 1:1 the lens is not f/2.8 but theoretically a bit lower than that, hence not quite f/5.6 in effective aperture terms.

I'm guessing that this is what explains the different minimum working distances with lenses of apparently the same focal length at macro range, ie at 1:1 they are not always the marked focal length.

Edit: on the MWD comparisons thing, see post #12 here http://www.talkphotography.co.uk/forums/showthread.php?t=251746