Teleconverter, 18-200VR and D80

[hemohemo]

Recently I had a chance to try a 3rd party teleconverter with the lens. Somehow, the combo couldn't really work beyond 70mm. I don't remember the brand and X factor, only remembered it as white.

A few questions though:

1. Why does it work only on the lower range? I had VR turned off during test. The cam kept hunting to focus, i.e. you see the focus cycling through blur-sharp-blur. And I managed to snap two pics at around 50 to 70. Anyone with similar experience?

2. Is it advisable to get a teleconverter to extend the fl ? Pros and Cons?

Thanks.

[Randius]

It is not advisable to use a teleconverter on this lens as you may damage it. As stated on Thom Hogan's review on the lens, "TCs also pose multiple problems, including loss of autofocus and potential damage to the rear element of the lens."

[psychobiologist]

Originally Posted by hemohemo Recently I had a chance to try a 3rd party teleconverter with the lens. Somehow, the combo couldn't really work beyond 70mm. I don't remember the brand and X factor, only remembered it as white. A few questions though: 1. Why does it work only on the lower range? I had VR turned off during test. The cam kept hunting to focus, i.e. you see the focus cycling through blur-sharp-blur. And I managed to snap two pics at around 50 to 70. Anyone with similar experience? 2. Is it advisable to get a teleconverter to extend the fl ? Pros and Cons? Thanks.

your AF works only when there is enough light, so on the TC, at 70mm and below, on the teleconverter, there is still enough light for AF.

but when it goes further than that, there will be too little light.

no you shouldnt use a TC on this lense, degrades image quality, and this lense its output is acceptable straight, will be worse if teleconverted.

TC should be used on lenses that can be sacrificed on a couple of stops, i.e F2.8 Glasses, F4 glasses etc

[psychobiologist]

forgot to add, AF is fine at F5.6, and F6.3 perhaps.

but on a TC, you lose a stop plus of light.. depending on the TC design

[hemohemo]

Thanks Randius and psychobiologist.

Obviously I must have missed the "limitation section" of this review http://www.bythom.com/18200lens.htm.

You guys are really great.

cs.