the mystery of the unsharp lens!

There's nothing that defeats the joy of a new lens like lack of sharpness. I just bought a copy of the Tamron 17-50mm 2.8 second, and, like anyone else, immediately started playing with it. Now, I had heard quite a few things about how sharp this lens is supposed to be, and I know with 3rd party lenses, the quality can tend to vary, but I was still VERY disappointed with the photos kept turning up at soft at 2.8.

Then, a small epiphany! The lens had come with a Tifffen UV filter (a cheap brand). So I did a little experiment to test the sharpness (aside from cropping, all the photos are straight out of the camera).

Here we have the original, uncropped shot.

100% Crop @ 2.8 WITH filter

100% Crop @ 2.8 WITHOUT filter

Yikes! Look at the difference! That's the equivalent of wearing and not wearing glasses for me. 

Now to get comparable sharpness WITH the filter, I had to stop down to 3.5.

As you can see, even now, it's not quite as clean looking. What's more, the colour appears a bit washed out too, with the black looking more grey-ish. Plus, at 3.5, it pretty much defeats the purpose of a fast lens. 

Moral of the story? Don't stick a cheapo filter in front of an expensive lens. Invest some money to protect your glass and not compromise on quality. 

I'm just glad this comes with a hood :)