Craig Shearman , Feb 01, 2010; 01:31 p.m.
Gregory, I'm not familiar with the Rokinon but aren't you at least using the auto function on your Vivitar? If you look at the color-coded settings on the dial, you can set it for a choice of four f-stops. Set the matching f-stop on your camera and you've got automatic operation. People who like TTL say the exposure is more accurate than standard auto exposure like on the Vivitar, so it might make things a little easier, especially compared with full manual. But a properly exposed photo with the Rokinon isn't likely to look any difference than a properly exposed photo with the Vivitar.