105mm AFS VR, but doesn't go down to F2.8 at macro

[thomson_chan]

Hello all,

 

I've been wishing to buy a macro lens, especially the 105mm, as the old AF-D version is no longer available, I've

had a try on the new one in a shop.

 

But the shop assistance pointed out to me that when the lens is at close focus, the min F number goes up, it

couldn't do F2.8 all the way to 1:1 macro.

 

Is this the same case with the older version?

Or does anyone know why? or any experience to share?

 

Cheers,

Thomson

[michael_bradtke]

<p>Yes the old one does that and yes it is normal.<br>

The camera is giving you the effective aperture. It changes as the lens focuses closer. It is f/2.8 at infinity not at its closest focus</p>

[raymond_ocampo]

<p><a href="../bboard/q-and-a-fetch-msg?msg_id=000FIP">Effective f-stop</a> is your friend.</p>

[Michael R Freeman]

<p>ANY lens will do that when focused to very close distances. It's know as the <a href="http://www-unix.oit.umass.edu/~rbhome/bellows15.pdf">bellows factor</a> . Simplistically, as you focus closer, the image circle produced by the lens gets larger. Because the same amount of light is still coming through the lens, but is now spread out over a larger area, the light intensity decreases. So the "effective aperture" gets smaller (the size of the actual physical aperture opening doesn't change).</p>

<p>No lens that is f/2.8 at infinity will be an effective f/2.8 at 1:1, although there are "optical design tricks" that can be employed, and in fact are used in both autofocus 105mm Micro-Nikkors, to reduce the effect. The advantage of the AF 105/2.8D and AF-S VR 105/2.8G Micro-Nikkors is that you get to see this change in effective aperture displayed numerically in the viewfinder. But the effect is present with all lenses, whether the camera display shows it or not (for lenses that appear to show a constant aperture, you will see the shutter speed slow as you focus closer).</p>

[paul_garland]

<p>The 105 mm AF-S VR is still one really fine lens!</p>

[Wouter Willemse]

<p>On all recent Nikon cameras you will see the effective aperture, also with 3rd party lenses (at least with the Tokina 100mm f/2.8).<br>

And since it's hard to find a non-sharp macrolens, consider the 3rd party lenses too. Lovely as the 105mm VR is, the tamron 90mm and tokina 100mm are both quite well regarded too and a lot more affordable. Just a consideration in case the budget has a limit :-)</p>

[chris_brandstrom]

<p>Indeed, my Tamron 90 does the same. And as the poster above mentioned, many third party macros are very nice. My Tamron is very sharp. It does not focus internally, nor does it have VR, but it is very light weight. I get f/2.8 if I'm focused at about 12 feet and further out.</p>

[oskar_ojala]

<p>You can buy the Zeiss 100/2; it will really be f2.8 up close ;-)</p>

[walterh]

<p>Lol Oskar I am still waiting for funds for the Zeiss.<br>

Now that I know it is 2.8 close up I need it even more .-)</p>

 

[jwallphoto]

<p>What do you shoot wide open at 1:1?!</p>

[thomson_chan]

Thanks all for the answer

 

There's more for me to learn.

 

I had thought about buying 3rd party lens, but as I'm still gathering the silvers for it, I'm doing the research of which one to buy.

 

I was just curious as to why it didn't seem to do what it says on the tin, but now I know.

 

Cheers

T.C.

[bjørn rørslett]

<p><em>"What do you shoot wide open at 1:1?!"</em><br>

<br>

Lots of stuff. Even useful with larger apertures such as f/1 (effectively f/2 at 1:1) or bigger. As with any other field of photography, close-up has no rules set in stone.<br>

<br>

</p>