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From: Desmond on 17 Dec 2009 07:11 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 Desmond.
From: Chris Malcolm on 17 Dec 2009 11:09 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. But you don't supply any detail, so I'm just guessing. -- Chris Malcolm
From: David Ruether on 17 Dec 2009 11:20 "Desmond" <otuatail(a)googlemail.com> wrote in message news:2564fad2-2794-4816-9b7d-2c34b2e2c24e(a)m26g2000yqb.googlegroups.com... > 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 > > Desmond. Anything marked ".**x" is telling you the "multiplier", as in, a ".42x" multiplies the focal length of the lens by .42 (.42xFL=new-FL with the attachment on). Anything below "1x" indicates a wide-angle attachment, and the lower the number, the wider (and anything below .42x is very unlikely to cover the full frame). These generally introduce considerable "barrel" distortion, even if only moderately wide (the .66x Raynox [their best one] is the only near-exception I know of), which increases as the ".**x" number gets smaller. These attachments vary widely not only in inherent quality but in how well they match the particular lenses they are installed on, making selection without trying before buying difficult. "HD" indicates that (if true!) that the wide-angle lens converter is a high quality one, intended for HD video cameras - BUT, camcorder WA converters are rarely very good on high resolution still cameras unless the ".**x" number is small (and will produce a round fisheye image). --DR
From: Rich on 17 Dec 2009 16:03 On Dec 17, 11:20 am, "David Ruether" <d_ruet...(a)thotmail.com> wrote: > "Desmond" <otuat...(a)googlemail.com> wrote in messagenews:2564fad2-2794-4816-9b7d-2c34b2e2c24e(a)m26g2000yqb.googlegroups.com... > > 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 > > > Desmond. > > Anything marked ".**x" is telling you the "multiplier", as in, > a ".42x" multiplies the focal length of the lens by .42 > (.42xFL=new-FL with the attachment on). Anything below > "1x" indicates a wide-angle attachment, and the lower the > number, the wider (and anything below .42x is very unlikely > to cover the full frame). These generally introduce considerable > "barrel" distortion, even if only moderately wide (the .66x > Raynox [their best one] is the only near-exception I know > of), which increases as the ".**x" number gets smaller. These > attachments vary widely not only in inherent quality but in how > well they match the particular lenses they are installed on, > making selection without trying before buying difficult. "HD" > indicates that (if true!) that the wide-angle lens converter is > a high quality one, intended for HD video cameras - BUT, > camcorder WA converters are rarely very good on high > resolution still cameras unless the ".**x" number is small > (and will produce a round fisheye image). > --DR And they likely will never properly accommodate an APS sensor size. But fisheye lenses are almost all naturally aberrated at the edge so the image might be acceptable. Rule of thumb, the bigger the lenses in the reducer, the more likely it will work reasonably.
From: Neil Harrington on 17 Dec 2009 16:12
"Desmond" <otuatail(a)googlemail.com> wrote in message news:2564fad2-2794-4816-9b7d-2c34b2e2c24e(a)m26g2000yqb.googlegroups.com... > 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 I've never seen anything like that in ".18x" but there are a number of .42x lens converters on the market (there are usually a lot of them being sold on eBay), which have enormous barrel distortion and therefore produce somewhat of a fisheye effect. You should be aware that these are not true fisheye lenses (which are quite expensive), but devices which attach to the front of your camera lens, and are not likely to produce very sharp results. Technically the .42x would mean that your kit lens at the 18mm (wide angle) setting would effectively become about a 7.56mm lens. That is actually much shorter than the focal length of a true fisheye lens for the format of your camera (for example, my Nikon fisheye for the same size format is 10.5mm), and therefore would not cover the whole sensor in your camera -- it would produce a circular image covering only part of the frame. But that's assuming the ".42x" really is .42x, which might or might not be the case. That sort of gadget might be fun to play with for a while, and they are usually fairly cheap -- far, far cheaper than a real fisheye lens. Just don't expect very good quality results from one. |