boatman Posted May 29, 2010 Share Posted May 29, 2010 We have a pair of Patt 793 followspots which have given sterling service for nearly 40 years! Unfortunately, when getting them out of storage for next week's musical, we found the front lens on one had split into several parts. I've emailed Jim Laws and RB lighting to see if either has a spare, but thought I would just ask on here if anyone has a suitable lens lying in a back cupboard somewhere and would like to negotiate a deal. Link to comment Share on other sites More sharing options...
topsy100 Posted May 29, 2010 Share Posted May 29, 2010 Try Iain Dennis at usedlighting he often keeps strange bits and pieces Link to comment Share on other sites More sharing options...
boatman Posted May 29, 2010 Author Share Posted May 29, 2010 Thanks, I'll try Iain too. Link to comment Share on other sites More sharing options...
Brian Posted May 29, 2010 Share Posted May 29, 2010 Lens are very generic. You only really need to know the physical diameter and the focal length to find a spare. Link to comment Share on other sites More sharing options...
boatman Posted May 29, 2010 Author Share Posted May 29, 2010 Lens are very generic. You only really need to know the physical diameter and the focal length to find a spare. I can easily measure the diameter, but the focal length might be a bit more tricky. Is there a formula for calculating the focal length knowing the diameter and the thickness at the centre? Link to comment Share on other sites More sharing options...
bruce Posted May 29, 2010 Share Posted May 29, 2010 Since you've got 2 of them, measure the focal length of the surviving one. You'll need a distant source - the big yellow thing in the sky is ideal. hold the lens facing the sun, and move a board or piece of paper to focus the light to the smallest possible spot. You'll know you've found it when smoke appears. The focal length is then the distance from the plane of the lens to the board. It should even be possible to do the same thing with large fragments of the damaged lens. Link to comment Share on other sites More sharing options...
boatman Posted May 29, 2010 Author Share Posted May 29, 2010 Since you've got 2 of them, measure the focal length of the surviving one. You'll need a distant source - the big yellow thing in the sky is ideal. hold the lens facing the sun, and move a board or piece of paper to focus the light to the smallest possible spot. You'll know you've found it when smoke appears. The focal length is then the distance from the plane of the lens to the board. It should even be possible to do the same thing with large fragments of the damaged lens. It looks as though Iain Dennis may have one but he needs to know the focal length as well, so it's time for the gardening gloves and some superglue and see if that works. Link to comment Share on other sites More sharing options...
bruce Posted May 29, 2010 Share Posted May 29, 2010 As long as you can find a largish fragment with the 2 curved faces intact, you should be able to measure the focal length from that. Link to comment Share on other sites More sharing options...
rogers Posted May 29, 2010 Share Posted May 29, 2010 why not take out and measure the unbroken lens from the other one ? Link to comment Share on other sites More sharing options...
bruce Posted May 29, 2010 Share Posted May 29, 2010 Is that not what I said in the 6th post in this thread - "Since you've got 2 of them, measure the focal length of the surviving one. " Link to comment Share on other sites More sharing options...
boatman Posted May 30, 2010 Author Share Posted May 30, 2010 Yes, indeed. The problem being that the surviving follow spot is in use for the next week so it will have to wait until the show is over. Link to comment Share on other sites More sharing options...
RoyJ Posted May 30, 2010 Share Posted May 30, 2010 ;) Hi, two suggestions for you.If the lens is the same diameter as a patt93n, then I have a spare lens.You could also try Bob Morgan of the enlighten iniatiative in Sheffield,we work very closely with Bob,so if you like I can see if he has got a spre lens as he has quite a selection of bits and bobs.Let me know, and I'll try my best to help.As an alternative, I have 2 converted 2k follow spots which I'm looking to swap for 2x patt 818 follows as the others are too heavy to lift since having spinal surgery.Let me know if I can help, keep it illuminated Roy. Link to comment Share on other sites More sharing options...
boatman Posted May 30, 2010 Author Share Posted May 30, 2010 Hi, two suggestions for you.If the lens is the same diameter as a patt93n, then I have a spare lens.You could also try Bob Morgan of the enlighten iniatiative in Sheffield,we work very closely with Bob,so if you like I can see if he has got a spre lens as he has quite a selection of bits and bobs.Let me know, and I'll try my best to help.As an alternative, I have 2 converted 2k follow spots which I'm looking to swap for 2x patt 818 follows as the others are too heavy to lift since having spinal surgery.Let me know if I can help, keep it illuminated Roy. Thanks for the offer Roy. I'll need to measure the lens, but it may be a few days before I can get to it. I'll send you a PM as soon as I have that information. Link to comment Share on other sites More sharing options...
boatman Posted May 31, 2010 Author Share Posted May 31, 2010 ..Let me know if I can help, keep it illuminated Roy. Hi Roy, PM sent with lens details. Thanks. Link to comment Share on other sites More sharing options...
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