Just got a Sigma APO 500mm f7.2 for my Maxxum 7000i. It is an AF lens but for many subjects it cannot lock on them, unless the subjects are really contrasty. Is this normal for that class of lenses? Any one has experience ?

Will autofocus improve with a Sigma APO 400mm 5.6 or Tokina AT-X 400mm 5.6 ? Any one has used them ? Which on is better ? A comparison between the older non-macro (72mm filter) and the newer macro (77mm filter) will be also very helpful. Thanks in advance.

Please don't recommend any 300mm 2.8 + 1.4x. It will break my bank account.

-- Bo (chen9622@uidaho.edu), January 11, 1999

Answers

Hi Bo, I am Minolta user myself. You have 3 major problems.

1) You have a fairly "old" AF-body with only 1 AF sensor, The new Si body-serie will be much faster and more accurate.

2) AF is normally usable with lenses of f 5.6 maximum aperture or larger (4.5, 3.5, 2.8 etc.). If light conditions do permit it (plenty of light) it'll work with smaller apertures as well as you already have noticed it.

3) I am affraid you didn't pick a very good tele lens for AF, evenso f 7.2 is not too bad, it will be more likely a f8 or more in real life. Try it manually if you want to keep the lens.

If you can afford it, take a lok at Tokina's ATX 840 f 4.5-5.6, I use it myself and like it a lot. It cost $ 550 at B&H and gives you more possibilities than a fix focal.

Here is their link: http://www.bhphotovideo.com/photo/35mm/tokina/afall.html

-- Marcus Erne (mcerne@evansville.net), January 11, 1999.

Actually, the 7000i is second generation AF from Minolta and it came out in 1988. It has 3 AF sensors. An f7.2 lens is really too slow to get good AF performance with even the newer bodies. The Tokina AT- X 400mm f5.6 is a good lens and will AF on your 7000i.

-- Henry Richardson (henry_richardson@hotmail.com), January 12, 1999.