Path: ccsf.homeunix.org!CALA-MUZIK!newsfeed.media.kyoto-u.ac.jp!news1.optus.net.au!optus!news.optus.net.au!53ab2750!not-for-mail From: Steve Irwin User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.6) Gecko/20040510 X-Accept-Language: en-us, en MIME-Version: 1.0 Newsgroups: fj.comp.dev.digital-camera Subject: Increasing optical zoom Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Lines: 30 Message-ID: <41vpe.1982$Zn.92885@news.optus.net.au> Date: Wed, 08 Jun 2005 05:06:08 GMT NNTP-Posting-Host: 129.127.14.157 X-Trace: news.optus.net.au 1118207168 129.127.14.157 (Wed, 08 Jun 2005 15:06:08 EST) NNTP-Posting-Date: Wed, 08 Jun 2005 15:06:08 EST Xref: ccsf.homeunix.org fj.comp.dev.digital-camera:2111 Hi all, I'm looking at increasing the optical zoom of my Powershot A70 and wondering if anyone has had any experience/comments. At the moment I've made up a mounting plate so that I can attach a 8 times magnification monocular to the front of the camera. It works quite well, but the biggest problem is that sometimes 8 times magnification is too much. What I was thinking is to use some of my old SLR lenses as the objective lens of my own telescope. If I could get a -25mm lens (or something similar) and mount that between the SLR lens and the camera then that should form a telescope, with magnification F/25 (where F is the focal length of the SLR lens). Since I've got SLR lenses ranging from 28-400mm then that should give a nice range of magnifications. Obviously it would require some mounting brackets and a little bit of playing around, but that should all be fairly easy. I've had a go at the basic idea by using a 50mm and 28mm SLR lens back-to-back and it seems to work okay, giving about double magnification, but obviously the image is inverted because that is with 2 positive lens. If I can get a negative focal length as the "eyepiece" lens then that should avoid the image inversion. So...anyone know where to get a strong (~25mm) negative lens cheaply, or has anyone else got any ideas? Cheers, Steve