Manual Focus vs. Auto Focus

[T-Ray]

Hi-
I am trying to expand my lens collection for my Sony a100. I recently purchased a Sigma AF 75-200 f/2.8 for Minolta AF/Sony (older model). This is my first non Sony brand lens as well as shooting in MF mode. Even though is says it is AF, why can I only shoot in MF mode? I can only shoot is MF mode using either Shutter (S) or Manual (M) to adjust the shutter speed. I use the DMF (direct Manual focus) option to be able to turn the aperature ring. I guess I am not use this not showing up in my display screen.

When looking at other non Sony lens that may say AF in the name- if it is a non Sony, do you always have to use the Manual Focus mode even though it is a AF lens?

I am kind of confused. Can someone please explain to me? To get the Auto Focus mode to work, do I have to have a Sony lens? I have never used a non Sony lens until recently and am bit over whelmed with looking at Sigma, Tamron, etc... These brands may be compatible, but am I not able to use the AF mode or the Sports mode?

Sorry if this is a dumb question, but I am just trying to understand going forward when looking for a non Sony brand lens, and what exactly I am getting - since Sony lens's are a bit more pricey.

[bono]

There are some rare old Sigma and Tokina lenses that don't work on the new cameras. Some of them can be made compatible by changing the chip of the lens. I would ask the Sigma-Service if an chip update is possible and what they charge for it.

I bet you mean this lens: Sigma*75-200 F2.8-3.5* lens for Sony Alpha - Minolta camera mount

There is no hope for a chip update for that lens - check first on Dyxum before you buy an old lens. Just sell it on ebay again - there are plenty of folks around with old film cameras.

[DonSchap]

Originally Posted by T-Ray

Hi-
I am trying to expand my lens collection for my Sony a100.

Before you run out and just willy-nilly pick up cheap/old glass for your photography, I invite you to bust-a-glance at the DCRP SONY DSLR Forum.( <- Click on link)

If you SORT on the thread "ratings" and pull up the five-star stuff, you will find yourself with a knowledge base that rivals any on the web. Just read through it and learn to save yourself some time and money. It all started with the a100 and has grown from there, so you should be right in the driver's seat. Then again, why deny yourself the pleasure of "toughing it out" on your own and spending thousands to learn the same thing?

Hey, it is just a suggestion to QUICKLY get you the type of important info you will need to grow your craft. Please, enjoy.

[T-Ray]

Thanks- I returned it to the buyer and got a Tamron lens (70-200 f/2.8) from B and H Photo. It was pricey, but about half the Sony lens.