Tamron TC: SP or non-SP?

[obi-wan-yj]

<p>I'm in the market for a 1.4x teleconverter. The Canon model isn't an option, because I don't own L lenses. This will be used initially on an XTi/400D crop body, but eventually on either a 50D or 5DmkI. It'll most often be used on a 70-300 IS lens, but occasionally on a cheap 500/8 or in various macro configurations. Until I can shell out the cash for a longer macro lens, my current favorite macro lens is a 55/2.8.</p>

<p>I'm currently only looking at the Tamron TC's, but I'm torn on whether to get the SP model ($180) or the non-SP model ($110). From Tamron's web site (http://www.tamron.com/lenses/tele-guide.asp):</p>

<p>"<strong>Tamron Teleconverters: Standard vs. SP-Which do I need?</strong></p>

<p align="justify">Universal-type teleconverters have certain limitations in performance when used with ultra-telephoto lenses of 200mm or longer as compensation of chromatic aberration alone becomes highly critical in this focal length range. The new PRO-series teleconverters are specifically designed and optimized for use with such ultra-telephoto lenses to deliver maximum resolution, contrast and color rendition without degrading any aspect of the master lens performance.</p>

<p align="justify"><strong>Tamron SP Pro-Series Teleconverters</strong></p>

<p align="justify">The SP AF PRO-series teleconverters, with a newly designed optical construction (4-group/5-element for 1.4X and 4-group/7-element for 2X), are designed to be used with lenses that are F/2.8 and of focal lengths of 90mm or greater. This would make the use of the SP teleconverters ideal for the Tamron SP90mm F/2.8 macro, 70-210mm F/2.8 and 300mm F/2.8. Relative illumination is significantly improved resulting in better overall contrast and resolution across the entire image field. In addition, chromatic aberration and astigmatism are better compensated for by virtue of the use of higher-grade glass materials and more sophisticated design techniques than used in universal-type teleconverters. When used with lenses with smaller maximum apertures (F/4 and F/5.6, for example), there will be little difference in image quality as compared with the standard Tamron teleconverters. When used with lenses wider than 90mm, the SP teleconverters can actually comprise [compromise?] image quality.</p>

<p align="justify"><strong>Tamron Standard Teleconverters</strong></p>

<p align="justify">The standard Tamron teleconverters extend the focal length by a factor of 1.4 or 2 respectfully and sustain the same light loss factors as the Pro-series. 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's."</p>

<p align="justify"> </p>

<p align="justify">OK, so my current primary macro configuration may see reduced IQ with an SP teleconverter, but CA will be reduced on longer telephoto lenses. Does anybody have any first hand experience or examples you can share that compare the two? What does an SP TC really do to a 55/2.8 lens? Is there a difference in quality at the corners (in case I switch to a full frame 5D)?</p>

[jcolwell]

<p>The Tamron SP AF 1.4x teleconverter that I have is almost as good as my Canon EF 1.4x Extender, and it's a lot smaller. I've heard many people say good things about the Kenko Teleplus Pro 300 teleconverter series.</p>