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From: Truer Info on 18 Dec 2009 15:57 On 17 Dec 2009 16:09:33 GMT, Chris Malcolm <cam(a)holyrood.ed.ac.uk> wrote: >Desmond <otuatail(a)googlemail.com> wrote: >> Hi can anyone help on tech talk. I was looking at a range of fish eye >> lens. for Sony A200. >> I am comming across .18x .42x also HD > >> Can someone explain these please > >My guess is that you're not looking at complete lenses, but at fish >eye lens extenders which screw onto the end of an existing lens. If so >the numbers are the focal length change factors. The effective fish >eye extended focal length is then the base lens focal length >multiplied by that factor. You then look up the focal length fields of >view angles for your camera's sensor size to get the angle of view. >If so it's not the camera you should be trying to match but the lens >you're extending. If so note that some of those extenders are of >pretty dubious image quality. And some are of excellent quality. I have one marketed at 0.25x, but in real-world tests it comes out at 0.33x. Still a strong contender as far as optics go. I have used it on 5 different P&S cameras and in all cases it has provided full-circle fish-eye views that rival and beat those coming from a $2,500 Nikkor fish-eye lens in CA and sharpness performance. When used with the camera's own zoom then it provides exceptional wide-angle views from 9-11mm full-circle fish-eye frames up to 38mm wide-angle views. Seamless zoom range from full fish-eye, to ultra-wide-angle, to wide-angle. Where the camera's own lens then picks up on its own without any adapter. All without impinging on the camera's own available apertures. All this for under $100. Try to buy any f/2.0 fish-eye or ultra-wide-angle lens for any camera at that price and one that works as well. For that performance and price I'll forgive them their .08x difference in marketing ploys. |