Lens Recommendations Please

[Kit]

O.K, I've been good and saving up my $$$ to purchase a new camera and lens. I know I want the Pentax K-5 and I was also thinking of investing in a 70-200 f2.8 lens, but just wondering what all you knowledgable people would recommend?

My main subjects are children. I have a sigma 18-55 kit lens but mostly use my 50 f1.4 for my work. Also have a few other lens but none worth mentioning.

I'm happy to invest in good lens and would eventually like to have a few more prime lens in my kit, but for now, looking for a nice zoom lens.

[i speak in math]

Originally Posted by Kit

O.K, I've been good and saving up my $$$ to purchase a new camera and lens. I know I want the Pentax K-5 and I was also thinking of investing in a 70-200 f2.8 lens, but just wondering what all you knowledgable people would recommend?

My main subjects are children. I have a sigma 18-55 kit lens but mostly use my 50 f1.4 for my work. Also have a few other lens but none worth mentioning.

I'm happy to invest in good lens and would eventually like to have a few more prime lens in my kit, but for now, looking for a nice zoom lens.

The sigma 70-200 f/2.8 is pretty well regarded. The Pentax 50-135 f/2.8 is better optically and gives you the weather sealing. But it comes at a price, and you have to worry about the SDM. I'd probably stick with the Sigma HSM

[Kit]

Thanks for the reply. I was just wondering if I should invest in the Sigma Pentax APO 70-200mm F2.8 EX DG HSM Telephoto Lens or the Sigma Pentax 70-200mm F2.8 EX DG OS HSM Telephoto Lens. There's a huge price difference but I was wondering if the OS function is worth the extra $$$ considering the pentax has an inbody stabalization system.

[i speak in math]

I wouldn't recommend the OS version over the non-OS. The pentax body already has a reliable SR system. I have no problem getting 4 stops of SR over the focal length rule of thumb using it. I don't believe the effects of the two stabilization systems work together. So, its hard to justify swapping SR for OS when they do the same thing.

Non-OS should be just fine.

[Kit]

Thanks for that i speak in math. I'm glad that you made that suggestion because the price difference is huge. Now to go shopping