I've never been a big fan of teleconverters. I've always worried about distortion, blurry corners and, of course, loss of light through them. That says nothing about adding more glass and the flare that can be generated that way. But this wide angle shooter doesn't like to spend a lot of money for long lenses because I don't use them very often. My shooting style is usually up close and personal. I thought I might try a teleconverter to see if that might add some useful focal length to the long end of my lens arsenal. Who knows, it might work out well. I chose the Tamron 1.4X for a number of reasons. In the first place, it is a modest, simple 4 element unit that is small, light, and not likely to have as many optical nasties as one of the higher magnification units. It would only lose a single f stop of light. Tamron has a well deserved reputation for producing good optics. Also, it was affordable at a little over $100 from B&H. My longest lens is a beauty. It is the 300mm AF Nikkor F4 ED. It is crisp and sharp and has virtually no aberrations that are visible in photographs. So the teleconverter would turn it into a 420mm f 5.6 - certainly a nice addition to the lens collection at a very affordable price. New lenses go through a lot of tests at my place before I put them to use. I'm not going to bore you with the details of what I do to test lenses but I will at least deal with the issue of sharpness here. The image below is a newspaper page shot at near minimum focus - around 5' for this 300mm lens - with the Tamron teleconverter in place. Here's the full frame image: As you can see the setup produces crisp, sharp images with good detail. Remember you're looking at a 72 ppi jpeg. Note that the straight ruler lines on the edges of the newsprint remain straight. That means that this well corrected lens stays well corrected even with the teleconverter in place. No pincushion distortion is visible at all. The second image is a blowup of the lower right hand corner of the frame to test for corner sharpness. This is more than I expected, to tell you the truth. I know the 300 Nikkor is tack sharp in the corners but I didn't think that could be preserved with an inexpensive teleconverter. I was impressed with this result. In a nutshell, I consider the Tamron 1.4x teleconverter to be a truly outstanding optical accessory for your long lenses. Yes, you will loose a very slight amount of contrast which you can restore in post processing. Yes you will lose an f stop of light. But the overall ability of this product to produce sharp images is certainly there. It is a keeper.