2X teleconverter

does using a teleconverter distort images at full zoom with a 70-300 MM lens

than it would if just using a 600MM lens.

The way I understand it is that anytime you add more glass infront of your camera the quality is going to deteriorate. That being said, the higher quality the added glass, the less the deterioration. So if you were using a high quality 70-300 and a high quality telecoverter, it would be better than using an average 600mm. Thats just my take on things, I'm an amateur with little experence in teleconverters.

Absolutely right. Teleconverter is just an optic, and does what every other optic does.

I think AF vs. manual focus is more of an issue with a teleconverter.

I have a Sigma 28mm-200mm lens f3.5 to 5.6. I tried it with a 1.4 and a 2x Tamron teleconverter. With the 2x I needed allot of available light for it to AF. With the 1.4x I had no trouble even in low light. I really had no issues with the picture quality at the 1.4x. The 2x things did not seem as sharp. That could also be due to the fact that I had to use manual focus at 2x. Hope this helps.

Once upon a time I tested several teleconvertors shooting from a tripod of newsprint. I tested at the time (my best long lenses back in the late 1980s) a Sigma 400mm f5.6 APO, a 300mm Accura f5.5 (a cheap T-mount lens) and a Pentax 200mm f4 A lens. the teleconvertors I used included a Sigma Macro 2X, Pentax 2X-S, Pentax 1.4X-S, and Sigma autofocus 1.4X. The Sigma 2X Macro is a cheap teleconvertor that is interesting because you can screw out the elements and make it into an extension tube.

 

The results were pretty interesting. First of all the TC degraded the image a tad. The Pentax 1.4X-S was by FAR the best TC on all the lenses although the Accura really didn't perform well with any TC. The Pentax 2X-S was WORLDS better than the cheap-O Sigma 2X and the Autofocus Sigma 1.4X was ok but certainly less sharp than the Pentax 1.4X-S. It proved the old saying "You get what you paid for".

 

At the time I had just read an article by Lepp saying something about the Sigma 400mm f5.6 APO being able to return professional photos with a 1.4 X TC so I wanted to see for myself. In his tests the Tamron TC (now Kenko, I believe) was the best 3rd part TC (he didn't test any Pentax equipment)

 

The other issue of course is that with a TC lenses become slower so an f4 is effectively an f8 min aperture.

 

TC and zooms are another story. Problem number one is MOST zooms are not the optical match of primes. That isn't entirely true of course. The other problem is in metering is that you may not really have an idea what effective f-stop you were using if you had a TC and a zoom as the f stop is constantly changing as you zoom. Few people worry about that now-adays.

Also bear in mind that a 70-300mm zoom is typically not at its best at full extension; in addition to getting slower, most also get a little soft. As other posters have mentioned the teleconverter is not likely to improve the situation, if anything, it will make it worse.

 

-Andrew