What size lens do i need for this camera?
You just need any Minolta AF mount lens. Sony Alpha lenses also physically fit as Sony inherited the Minolta lens mount when they bought the company, but as they are a later development not all will be electronically compatible.
The size of the lens depends upon the focal length of the lens and you choose that according to how wide a field of view you desire. Typical lenses are 28 and 35mm wide angles, 50mm "standard" (approximately the same perspective of how the human eyeball sees images), 70 to 90mm short telephoto lenses (a narrower perspective and very good for portraits) and higher numbers are narrower perspective telephoto lenses for viewing increasingly distant objects. In practice, the available lenses will be incorporated into zoom lenses which incorporate a seamless range of focal lengths within one single model. The word "zoom" reflects the fact that you can seamlessly change from say 28mm wide angle through to 80mm short telephoto and every single setting between them
Any zoom which starts at less than 50mm and finishes in the short telephoto range is called a standard zoom and is the lens that most autofocus cameras were supplied with. The next most common size will be something like a 70-200mm which is a telephoto zoom (or tele zoom) and takes you from a portrait lens to a genuine 5x magnification telephoto. You may also find so-called "super zooms" which do the whole job on one, for example 28-200mm. but the more jobs a single lens tries to do, the bigger and bulkier it becomes and the image quality deteriorates due to poorer contrast and greater image distortion at each end of the zoom range.
This is not an exhaustive answer, as there are entire books on the subject, but hopefully it's been of help to you.
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