What lens are needed for a canon 50d to get the equivalent of 12x optical zoom on a p&s digital camera?

Choosing the right digital camera is just like choosing anything else. You have to figure out what your needs are and what you are going to want to have as far as the specifications and options are concerned.
By doing a bit of research, you can see that there are a lot of good quality digital cameras on the market and most of these will do a pretty good job.
But if you want the best for the money you should ask yourself some important questions ahead of time. Make a list of some of the following features:

- Megapixels (at least 5 or 6)

- Image Sensor Size (In this case, bigger is better . . . not megapixels, that's different . . . make sure that the sales person you are talking with knows the difference)

- Zoom Lens (anything more than 12x or 70mm and you'll probably need a SLR) For most people 12x zoom is enough.

- LCD screen (at least 2.5 inches and 230,000 pixels)

- Image Stabilization (this feature is great for shaking hands and slow ISO settings)

- face detection / auto focus ( not essential, but could save a few bad pictures)

- Battery Performance (most cameras give a rating based on number of pictures you can take with a single set of batteries)

- Flash Recharge time (a slow recharge time can cause you to lose a few pictures)

- Camera Size (choose from ultra compact, compact, or extra case need just for lenses)

- SLR or point and shoot ( pros vs amateurs)

- ISO settings (if your into manual settings)

- Built In Camera Editing (things like removing red eye and custom flash settings)

- Macro Lens Function ( for photographers that like to take pictures of really really tiny things)

- Memory Cards (some take CF, some take SD, some take both . . . if you already own one or the other, that may help you decide)

If digital camera sales were any indication of what the best brand was, then according to Amazon.com, Canon would be a top choice for sure. As I write this, Canon manufactures 18 of the top 25 bestselling cameras on their best seller list. In addition, Canon holds 9 of the top 10 spots, with the top 3 being the PowerShot A570 IS, the PowerShot SD1000 Digital Elph, and the PowerShot SD850.
These three camera models have nearly out-sold the rest of the entire market.

Then there are the ultra compact digital cameras which are the smallest ones made. Many are quite good and sometimes a little more expensive than most and the quality can sometimes suffer due to their smaller size.