I forgot to do a review of the Tamron-F 1.4x Teleconverter so I figured I'd remedy that now. Not a very detailed review, but honestly you don't really need one for a teleconverter. It either does its job, or it doesn't, and in this case, the Tamron-F 1.4x does its job well for the price.
I originally bought the Tamron-F to help me out with baseball photography because I needed a little more reach on my Canon EF 70-200mm F/4 USM. I won't go into details now because my brief overview of teleconverters covers a lot of that. I ended up purchasing a used teleconverter from KEH Camera for about $66 shipped.
Other purchase options are on Amazon ($115) (sorry, I only found a Canon version) and eBay (see widget below):
Generally, used Tamron-F teleconverters have been going for $70-$80 on eBay. With no moving parts, I see no reason to not buy used.
My teleconverter came with two end caps and a leather (well, probably synthetic) carrying bag. The glass was pristine and it looked completely new and unused.
Oh, and as usual, all images in this posting can be clicked to see them larger.
In terms of functionality, the TC does what it's supposed to. It firmly snaps on between the camera and lens, provides all autofocus function on my 70-200 f/4, and feels very secure and natural. Obviously, a stop of light is lost (which isn't indicated on my 20D, meaning it'll still say f/4 when in fact I'm shooting at f/5.6). On the other hand, it magnifies the image by 1.4x, which is the whole point.
I briefly tried it on my Tamron 17-50mm f/2.8 (and it worked) but I recommend checking before you mount it on wide angle lenses because sometimes the tolerances aren't correct and you could damage internal lens elements.
Of course, for me, the real question was image quality. Will a low-end 1.4x teleconverter really improve magnification without damaging image quality too much? Will my Canon 70-200mm with the 1.4x TC out perform my Sigma 600mm? I've done a few quick experiments to determine the answer to both of these questions.
For both tests, I shot a portion of a magazine page outside in the sun on a clear day. Honestly, I probably should have picked a subject with more fine detail, but these images allowed me to answer the questions I was concerned with.
For the first question, I've compared the Canon 70-200mm @ 200 mm both with and without the teleconverter, upsampling the pure version to allow a side by side comparison:
Definitely, the teleconvert provides an image with better resolution and definition. Both images would benefit from sharpening and post processing, but these are pretty much straight JPEG conversions from RAW. This put my mind at ease, because I was quite concerned that the glass in the teleconverter would hurt image quality more than the benefit from increased magnification, but that isn't the case. Both these images were shot wide open and I found sharpness improves slightly if you stop down.
My general feeling after shooting over a thousand baseball images is that you don't get quite as much sharpness with the TC, but the added magnification is worth it. Also, I've found the larger viewfinder image is a huge benefit when shooting action!
Finally, note that there isn't a huge amount of chromatic aberration added by the teleconverter, a frequent problem with adding extra glass, especially discount glass. Definitely, a little is added, but not enough to cause problems (and easily removed in post-processing).
My next concern was whether the teleconverter added to my 70-200mm f/4 renders my Sigma 600mm f/8 unneeded. On one hand, I'd love to replace the big, bulky 600mm, but on the other hand, I have a special place in my heart for the all-manual Sigma, and it'd be pretty lame if my $100+ 600mm lens was beat by a simple teleconverter. To simplify comparison, I shot with the TC at f/8 (it read f/5.6 on the camera).
This one definitely goes to the Sigma.
Sure, the Sigma's contrast isn't as good and it's a heck of a lot harder to use, but it has the potential for a lot better image quality. In particular, look at the detail on the '$' on the middle-right edge. The 280mm equiv TC pretty much makes the vertical line disappear, while the Sigma catches it nicely.
So, overall, I'd say the TC is well-worth the $70 price for a used model. If you are going to buy new, I would probably recommend a Pro version, although I'm not completely sure how much of an improvement you can expect. But, since you can get a Kenko 1.4x Pro 300 DG new on eBay for about $130 (see widget below) -- if you are willing to buy from Hong Kong -- you'd probably be better off with that.
Personally, I think the Tamron-F 1.4x is one of the best deals out there since there's so many floating around on the used market. It's a very cheap way to get a little extra reach and there's only a slight difference in image quality (which is not what I hear about other cheap teleconverters).
Note this assessment DOES NOT apply to the 2x model; general consensus is that the Tamron-F 2x model has poor optical performance. If you need a 2x teleconverter, you should probably go after a Pro model.