增距鏡 = Teleconverter ? If you wanna use the teleconverter for your kts lens 17-85mm f3.5-5.6, I think you would not get what you want !
2x teleconverter will double up your lens focal ( 2x 85 = 170 then multiply with crop sensor 1.6x = 272mm ) this look good for you, you will get 272mm but this 2x teleconverter also will double up your aperture ( 2x 5.6 = 11.2 ), the problem come now, your 400D body AF ( auto focus ) will not work !!! ( for Canon enry level DSLR only support up f/8 only ).
It not not a proper way to buy a teleconverter for short range lens.
please visit to http://www.photomalaysia.com - insides this forum got a canon user sub forum 作者: usnameless 時間: 2008-5-15 01:45
What is your budget?
55-250
70-300
are both good. Also you may want to consider IS unless you plan on taking the tripod with you all the time. 作者: dumpdump 時間: 2008-5-15 21:14
after searching info, final decide sEF 70-200mm f/2.8L IS USm + Canon Extender EF 2X II is it good choice? 作者: mmr.ren 時間: 2008-5-16 12:48
A very good combination.