Tamron 90mm aperture at close focus

[WilsonvilleUSA]

I just picked up the Tamron 90mm f2.8 DI macro lens. First impression is that it will take some awesome pictures on the D70.
One thing I have noticed though is that at close focus (less than 8 feet or so) the aperture won't stay at 2.8, it creeps up to 3 or 3.2.

Is this normal? Can't find anything about it in the documentation or a search of Nikonians.

Can't understand the mechanics of why it would be happening either, any help or info?

Wayne Wilson
Bothell WA

[KerryPierce]

 AFAIK, this is normal, with any true macro lens. My 90Di breaks to f/3 at about 10ft. The closer you focus, the smaller the minimum aperture becomes.

[gooseberry]

What you're seeing is normal and is the correct behaviour. Most modern Nikon AF bodies will report the effective aperture. There is a relationship between the aperture on the lens and the effective aperture when focusing less than infinity. For most lenses this is neglible, but at macro focusing distances and magnification, the difference becomes large enough to not ignore.

For an explanation... see this link

http://www.nikonians.org/cgi-bin/dcforu ... e=threaded

[MHD]

yep... its normal... the micr-nikkor 105/2.8 does it too...

goes from 2.8 -> ~3.5 as you focus closer...

[birddog114]

I have the Tamron 90Di and it's the same. No surprise here.

[the foto fanatic]

When I first put my Nikkor 105mm micro on my camera, I noticed the same thing.
In fact I was a tad concerned until I read the instruction sheet that came with the lens (normally I just strap a new lens to my camera & shoot) and realised that the camera was going to show me the effective aperture.
Quite a good feature, once you realise what's going on.

[MHD]

yes a macro lens is the one lens where I had quite a detailed read too...

In the nikkor the lens is quite complex mechanically and many odd things happen!

[WilsonvilleUSA]

Thanks for all the info. I didn't see anything about it in the instruction sheet, I did look for it.

Feel all better now...just need to find some bugs!