From you OP is suggests that you want static stars rather than star trails so you need to consider the below to ensure that you avoid trails..
Based on the fact that you are using a full frame camera there is something called the "600 rule" for getting an image without the stars starting to trail, this is quite basic but works well, taking the 600 and dividing that by your focal length in 35mm format that will give the number of seconds that you can expose for without star trails showing 600/50 this gives you a 12 second exposure to avoid trails
So let's say you need a 12 second exposure

you then need to think about letting in enough light to pick everything up, now this is a balance of aperture and ISO, personally I never shoot wide open on the aperture when using a fast lens, most of my star images have been shot between f/3.5 and f/5.6 but for your instance if we stick to the f/2.8 aperture then you need to set the ISO to a high enough level to expose the scene without noise taking over the scene. It's all about striking up the right balance

personally I'd use a shorter focal length to increase the time you can expose
It's difficult without being totally aware of the subject and and lighting that is on it to say exactly what settings will be best but going with the below should be of some assistance
now how to do it, if you need a time that is available in your cameras programmed shutter speeds then you can set up the exposure values in manual, and then set a shutter delay and press the shutter to then take a exposure 2-10 seconds after you've pressed the shutter giving the camera/tripod to avoid camera shake
Ideally the best solution however would be to use a wired or wireless trigger to fire the camera, there will be a counter on the camera to show how long your exposure has been if your using bulb

but I don't think that you'd ever really need to use bulb as I cannot think of a time when you'd use a expousre longer than 30 seconds unless we start down the telescope and motor mount but that's a whole different ball game
Matt
MWHCVT