Tamron 1.4X F AF
(From company literature) The 1.4X teleconverter will increase the focal length of the master lens by 1.4X and make the lens one f-stop slower. The 2X doubles the focal length of the master lens and makes the lens two f-stops slower. In addition to increasing focal length, both teleconverters allow greater magnification in macro since the Minimum Object Distance (MOD) of the master lens does not change when used with the teleconverters.
The 1.4X teleconverter can be used with both AF and MF lenses. AF will be retained if the master lens is f/4.5 or faster. AF will be retained with the 2X teleconverter if the master lens is f/4.0 or faster.
Though using a teleconverter on wide-angle lenses is never really recommended, these converters can be used with lenses that are wider than 90mm and are ideal for all lenses that are not f/2.8 or faster.
Tamron 1.4X F AF
Tamron 1.4X F AF User Reviews
4 out of 10 points and not recommended by crmorse (11 reviews)CheapBad optics
I have used this TC with both a Tamron 70-300 and the Canon EF 28-135 on the Canon 300D Digital Rebel.reviewed January 4th, 2007 (purchased for $50)
Pictures taken from a stable tripod stopped down f/8 and low ISO are still somewhat blurred and have a noticable loss of contrast. In every instance where I have used this TC I later wished I did not when reviewing pictures
The last time I used it I setup a test where I used the 300mm with and without the TC and then compared uprezzing the non-TC shot to the same FofV as the TC shot and found that Photoshop does a much better job than this TC. Both sharpness and particularly contrast, suffer with the use of this TC.
The one pro for this TC is that it is cheap and built relatively solid. Additionally, it will give you the extra compression of the depth in a shot that a longer focal length provides. But that small benefit comes at a high cost.
My advice: don't use this TC. If you need a tighter shot just uprez in PS or buy a longer lens.
9 out of 10 points and recommended by Ross_Alford (36 reviews)Works well with most AF lenses, small, light, and high image qualitydoes not work with AF-S lenses
I bought this mostly to use with a Sigma 70-300mm zoom I used to own. I also ended up using it with a Tamron 28-300 I used for a while with my D70, and with a Sigma 18-200 I still use. It worked admirably well with all three lenses, though I haven't experimented with it at the wider end of the wide-to-tele zooms. It does not degrade image quality appreciably, and gives a nice boost to the reach of telephoto lenses.reviewed January 1st, 2007 (purchased for $79)
Combine the effect of this converter with the multiplier effect of an APS-C sized sensor as on Nikon DSLRs, and you can get amazing telephoto effects; for example a 300 becomes a 420, which is multiplied to a 630.
I don't use it much anymore because it doesn't allow AF with AF-S lenses. Still carry it occasionally when I take the D70 out with an 18-200 Sigma zoom; having this available increases the tele end of the zoom and makes the macro ability stunningly good.
Photo taken using this converter with the 28-300 Tamron:
Photo taken using this converter with the 70-300 Sigma