1 is good, 2 and 3 arent bad, pose wise, but you shouldnt shoot studio at 1.5, I keep all my studio shots between 8-11. I would not invest in a ring-light. A good ring light start around $800, for that amount of money you could purchase a 2 studio strobes with softboxes. We typically use ring-lights for high-fashion where the focus is more the clothes than the person. Not a good option if youre going to begin doing portraits because you arent able to sculpt with ring-lights. They produce an even lighting, which is fine for fashion and beauty but very limiting in portraits. And if youre shooting older folks you will see every single blemish and wrinkle
shooting chubby folks and theyll look twice as fat. With a soft-box set up you can create shadows and specular highlights which is the base for good portrait photography. You can also use what we call feminine lighting to thin out your subjects face. When I started out I was all about buying a ringlight until I had the opportunity to use one. They are great for the perfect complected, Kate Moss body types
very limiting to say the least.
So
the major question is how much do you want to spend? I know a lot of pros that just shoot with a single studio strobe and reflector with awesome results. Interfit sells a great set of strobes for beginners under $500. 2 heads, 2 softboxes and 2 umbrellas.
http://www.amazon.com/Interfit-EXD400-Softbox-Umbrella-Heads/dp/B002X75H60/ref=sr_1_19?ie=UTF8&qid=1323872855&sr=8-19I see you have the 70/200 2.8, I assume thats the L-series lens? Youre off to a great start with that lens, its the go-to lens for most pro Canon-Shooters. Stick with that lens, even in studio.
Your 580 ex is an awesome flash, and you could actually use that to shoot in-studio portraits, but youll have to get it off camera, on a stand, with at least an umbrella and with a remote. Pocket wizard sells the Flex remote system which in my opinion is the best remote for speedlite shooting off camera, because you can control the flash output from your camera. But its pricy - $428, for $100 bucks more you could get the basic Interfit strobe set-up.
http://www.amazon.com/Pocket-Wizard-MiniTT1-Transmitter-Transceiver/dp/B004FPYKIY/ref=sr_1_9?s=electronics&ie=UTF8&qid=1323873555&sr=1-9I would not go with constants because you have too much spill light and on black backgrounds, thats gonna light up the black. And youll have to shoot at 400-600 ISO which will result in grainy pics. It can certainly be done, and I have some examples in a post titled Glamour, but it is NOT the ideal set up, Constants are good for certain effect, excellent for still life and product but not ideal as the portrait go-to lighting set up. With strobes, you always shoot at 100 ISO for tack-sharp images.
The problem with your two studio shots was softfocus or motion blur, depth of field and hotspots. Be sure to use your focusing ring and focus right on the eye. Keep your f-stop between 8 and 11 for a broader depth of field and whatever lighting you choose, it needs to be diffused to prevent hot-spots. If you decide to go strobe, shutter speed is pretty insignificant in-studio. It needs to be kept between 1/60 and 1/250 and really only controls ambient light. I drop mine to 1/60 if shooting fashion on a white background to blow-out the white, 1/250 on a black back ground to make it deep black and control spill light.
If you have any other detailed questions, feel free to PM me. You are really off to a great start, keep it up!