I am having trouble figuring out my telephoto lens.

[topazsol]

I have a Sony DSLR- A500/ A550. The lens I use the most is a Sigma 28-80mm, with Macro at 80mm. I hooked up the Minolta teleconverter lens (Phoenix C/D7 DG 2x) to the other Sigma lens and it takes good photos until I try to zoom up to something, like a bird in tree branches or flowers across the street and then it refuses to focus and I can hear it trying to like crazy but it makes me wonder what good is a lens that allows you to zoom twice the distance but won't let you take the photo? What can I do to actually get the object in focus and to take the picture? How should I adjust my settings? Any help would be appreciated, thanks.

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[tirediron]

IIRC, this lens is an f5.6 at 80; with a 2x TC on it, it becomes something more than f11 which makes it dim enough that the auto-focus mechanism simply doesn't get enough light to do it's job. You'll be a lot better off getting rid of the cheap TC and putting some money into a higher-end tele-zoom.

[Hobbytog]

As the max aperture is about f11 the light is too low (not enough contrast) for the AF to work properly and therefore the lens will hunt and peck trying (in vain) to find something to lock onto. Just go on to manual focus and you should find you'll be able to take the shot.

[DiskoJoe]

most teleconverters wont work for focal lengths less than 50mm. So your lens is probably too short to use this in the first place.