Rastra? Raster is what you're looking for. If you're looking for printing information, I'd suggest browsing over to the forums at gigposters.com and reading through their forum articles on screen printing.

Split all the color and add a black color overlay if you're feeling nice. I don't know what you're really talking about with a halftone that has a 50% opacity, but when sending a file to the printer everything needs to come out a flat black (no grays). If you want a lighter color, change your halftone or spot color, don't mess with opacity. Have the file ready in the size you want to print it. And when printing, I prefer to trap the files myself instead of having the customer doing it. Also, always send a mock.

http://www.mintees.com has some great resources about apparel printing and there's always http://www.t-shirtforums.com/ There's not one solution, it really depends on your artwork and what you want to achieve. Good luck.

You have to be designing at full opacity, but you can adjust the transparency of the image prior to creating your halftone, which will affect the spacing of the dots. Halftones are great because you can extend your color range by layering, but remember to change your axis with each layer. You can also do this with cross-hatching, which, if applied judiciously, can generate some really nice variety in your design.

Worthey IFC said: Split all the color and add a black color overlay if you're feeling nice. I don't know what you're really talking about with a halftone that has a 50% opacity, but when sending a file to the printer everything needs to come out a flat black (no grays). If you want a lighter color, change your halftone or spot color, don't mess with opacity. Have the file ready in the size you want to print it. And when printing, I prefer to trap the files myself instead of having the customer doing it. Also, always send a mock.

This is why you should also get yourself a Pantone guide so you can label your layers with the color ink you want them printed at. Generally you'll have the option of designing with between 4 and 10 colors. Depending on what kind of software you use you might have to buy a guide. I use Corel, so my Pantone guide is built in.

As far as whether vector or raster is better, that really depends on you and your hardware. Raster can give you some really nice effects, but if you want something printed all over, your system has to be able to handle a pretty large file since scaling up with a raster will destroy your quality. I like to work in vector because it's scalable. My computer's a piece, so I like the ability to work small and resize my designs to whatever is needed.