Stacking Teleconverters.

[RbrtPtikLeoSeny]

As far as I know, you can put more than one tele converter on a single lens. Like, you can put a 1.4 and a 2.0 on at the same time right? It would just reduce the image sharpness and slow down the AF right?

Well, if you can stack two, can you stack more than two? Like, throw on 3 of the 2.0's? Or 2 of the 2.0's and a 1.4 or something like that? And that many Tele-cons would pretty much destroy image quality wouldn't it?

[Rokkorfan]

Refer the sticky "teleconverters" thread.

[Jon]

Let's see. You start with (for argument) a 300 f/2.8. Add a 2x TC, you're at f/5.6 and 600 mm. Add a 1.4, you're at f/8 on an 840. Add another 2x and you're at f/16 on a 1680. Now at f/8 your 1D series can still autofocus, but your Double Digit D line can't any more. At f/16, even your 1D series can't, and you're looking at a really dark screen that you're going to try to focus on. And you'll need a rock-steady tripod for all that, too. Plus the image degradation for a teleconverter. Let's take George Lepp's numbers - 10% for a 1.4x, 20% for a 2x. So with the first 2x, you're at 80% image quality. Add the 1.4x, and you've lost 10% of that, so you're at 72%. Add the second 2x and lose another 20% on that for about 58% of the original lens' quality. If you've got it focussed on your subject (see aperture in play) and if you've held it steady enough. Time to hitch a ride a few miles closer to the subject, I think.

[condyk]

For fun I just tried it with my 50mm II 1.8, Kenko Pro 2.0x and 1.4x together. It sucks :-)

Normally, they are both very sharp used individually and deliver good results. Together, AF hunts around, though does lock eventually, and images degraded, as Jon outlined! Not that much fun after all ... why bother?

[Buttkicker]

This shot of the moon was taken on a 300mm f4 Lens with stacked converters

http://www.chrisprocter.plus.com/Stars/moon.jpg

[jyrgen]

This one with three TC-s:

http://www.hot.ee/jyrgen/050416_1302.jpg

[RbrtPtikLeoSeny]

Looks to me like 3+ tc's are great for astrophotography! :-) Great shot! Very defined craters.