Aperture and ISO setting for first time shooting star trails

Hi guys I'll be shooting at Yosemite this weekend and wondering what setting is best to shoot star trails.

I have a Canon 5D2 and Sigma 50mm F1.4

I plan on shooting for 30 minutes with a 30 second exposure for each frame.

My question is does it make a difference if I shoot at F1.4 with a ISO 800 or will I get better results with F2.8 and ISO 3200. Both give the same exposure but wondering if any experienced star trail shooters can advise if a certain setting will give much clearer images.

Thanks guys!

It'll be a trial and error for sure. Now on the 50mm lens, if you want to avoid star trails, try using rule of 500 & 600. 600 divided by the focal length 50mm will give you 12 seconds. If you inspect it and see a trail, try 500 instead.

If you have a wide angle lens you'll have more time for the exposure. 10mm for example will give you whopping 50-60 seconds without the star trailing.

When shooting for star trails you don't really need to use short exposures - because you're obviously not worried if the stars trail in individual images.

I would tray a couple of test shots first. I'd start at f1.4, ISO800 and 20s exposures. Then I'd increase ISO and Exposure times to see how high I could go before noise and/or light pollution got too bad.