I currently have a set of close-up filters. They work pretty well for isolated subjects with distant backgrounds where the distortion is unnoticeable (eg.: flowers, insects on plants, etc.), but the distortion and severely shallow DOF make any of these shots difficult and clear shots of things on straight surfaces impossible. I can get a really cheap (as in, less than $30) set of extension tubes on eBay without any CPU contacts and only use my 50mm manual lens. Should I spend more and get extension tubes with CPU contacts for metering or spend a bit more yet for a used proper macro lens?