Problem with Tamron Macro

Just noticed a problem with my Tamron 90mm Macro, i'm getting a bright spot in the centre of the frame. This is not really noticable until I stop down further than f8, its barely visible at f9-10 but becomes more pronounced the smaller I go, and at f32 theres a definate "spot".

This is obvious aperture related as the circle gets smaller as the aperture decreases, looking through the lens at the aperture blades they dont seem to be closing down evenly but not really having another to compare it to I dont know what they should look like, I do know its not as even as my Pentax lenses and they have less blades?.

Any suggestions?

I don't have that lens but I'd suggest any lens where the blades don't close down evenly has developed a fault - if it's still under warranty then I'd send it back to Tamron for repair/replacement.

Just took a few shots the other day at f32 with no noticeable spots.
I'll try to photograph the blades later today and let ya see what mine look like for comparison. Assuming someone doesn't beat me to it.

Other than that, I agree with hefty1.

If I recall you have an older 90mm f2.5 model, the same as mine :
I hope you haven't killed it

Not sure if it will be a viable candidate for repair though. But i hope so

is there a UV filter on the lens?

My Tamron 90mm F2.5 dislikes UV filters and produced a similar fault to this when i was using one with it.

Hope it turns out to be something nice and simple.

Is this the adaptall-2 version? I had a similar problem with mine in bright sunlight. Funnily enough it seemed to go away when I got a new AD2 mount, but that might just have been my imagination!

Are you using a lens hood?

Thanks for the input chaps.

The lens still seems to perform well in all other respects so I may just learn to live with it.

Mongoose:
Yes I tried it without a filter.

Clarky:
Yes it is the same, do me a favour and try yours for me. just point it at a plain wall or piece of card the same as you would if checking the sensor for dust (which is how I found the problem with mine) Reading the other replys it might just be something peculier to Tamron macros.