Tamron 90mm macro f2.8 - variable aperture at close range??

[Melee]

Hi all you macro gurus out there,

I just bought a 2nd-hand Tamron 90mm Di f2.8 macro lens from a fellow CSer. I've found that I can only get the maximum f2.8 aperture when working at 3m distance or greater. Any closer and the maximum aperture progressively reduces. At its minimum focusing distance (about 30cm), the maximum aperture is only f3.8.

I was told by the seller that this is 'normal'. Just wanna check with other CSers: is this your experience with this lens/other macro lenses? Or did I just buy a defective lens?

Thanks for your input!

NB: I'm using the lens on a Nikon D80.

[catchlights]

yes, it's the way it works.

at 1:1, you lost one stop of light, so it is f3.8 (f4)

[Melee]

Thanks for the quick reply! Feel much better now....

[Goldenstars08]

Originally Posted by catchlights yes, it's the way it works. at 1:1, you lost one stop of light, so it is f3.8 (f4)

Thanks...Learn something new...
I own this lens before for my canon system, how close even 1:1, my F-stop is still F/2.8 if i set it atF/2.8...

[Scaglietti]

Nikon bodies display the effective aperture for macro lenses, Canon's doesn't. But it shouldn't affect anything.

I think at minimum focusing distance the max effective aperture of Tamron 90mm is f/5.6.

BC