I bought a coated flat 8inch made by Diane Lucas plus a bunch of 3 a guy made with the 3 disk method who polished but never finished and a number of elliptical secondaries and some smaller ones I suspect are flats too. Now I have to try to test them to determine what the tolerance of them.
There is a learning curve but I'm sure the reason most ATM have trouble with this test is in getting collimation of the flat with water. I use a laser in my setups and video but it's not perfect and I can be off enough to where the fringes can't be seen, (they are actually there but spaced so close that you can't see them unless you actually get down close and use a magnifier due to too much tilt). So if you really can't get a laser to work you can make an autocollimator using a cheap dime store refractor (there were about a half dozen locally on Craig's list under $25) putting a LED source in a low power eyepiece. The tripod and mount are good for aiming straight down too. Fine pitch leveling screws are very helpful too. As far as the light source a neon lamp has a bunch of emission lines but I've used one as did Texereau but I can't compare it to a mercury lamp. I use a F4T5 BL (black light) which can be found on Ebay but the fixtures are harder to find. I use Kitchen and Bath fluorescent lamps where I need to do contact testing, they seem to be the best fluorescents. LEDs don't work BTW. I would advise learning on a small uncoated flat where finding a small lens for a collimator isn't hard. When that's mastered then try a coated mirror and cerium oxide to cut down the intensity. Measuring the water thickness is important as well, 1 mm is good for large mirrors perhaps less for smaller optics.
I haven't tried glycerine but it's higher viscosity would cause either a thicker level or a very long wait for leveling plus a lower reflectivity due to a higher refractive index closer to glass.
Great Video. Thanks for posting. I was not able to hear where the fresnel lens cam from. Could you give me that information again? Thank you and best regards, Francis J. O'Reilly
No I never tried glycerine but I did find out that the refractive index of pyrex and glycerine are almost identical. Unless you tested an aluminized mirror you wouldn't see any fringes! Ed
You sometimes find Fresnel lenses like this one on Ebay 360 dia. X 900 FL:www.ebay.com/itm/184044724952?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D234205%26meid%3D211a999515454ed9b01fef9224701ee3%26pid%3D101195%26rk%3D1%26rkt%3D12%26sd%3D263133862803%26itm%3D184044724952%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseWithPLXWeb%26brand%3DUnbranded&_trksid=p2047675.c101195.m1851&amdata=cksum%3A184044724952211a999515454ed9b01fef9224701ee3%7Cenc%3AAQAGAAACAMoYPKgvuVfeKcYviaxs%252BPjyVNVrp31VE6oWAL40ib5fKrKwsgEpXt13eTpqf8TglYPvGm3U8x85fAXKlk0DRdSzW4el%252FyzQnMCuHJHBflSHLtc8B6HX%252Bz4JRSJsGRz%252BuHp1k4Db4owFouuaw2ejfpRXnaPqEpeRWDtpFws6Dhu8rZu0h4F8R8OqNSw1etM2aEcLnS8d1P2YQiQj7K%252F5%252BUG9kBVcvkl9Kks2xPRtYbvWSKjJENLX3WIRIl7BJuaizTDJ1IBrh9EBFi8Ev6CPtiOmAucy30BB5uApvGzA%252BWGgHSY%252BX04IuKNa21k074bTE0DeDqg0Hc%252ByMzQfMsiF5Yqujw2yq5ONqCYUaLcIaad12gqMOCT0lWdQRwp1MRahX836yTbpA8wRvkCfaGE8AfmZ70lFY9r97Mu6yTSnn06Qgmi8OmcLtPqF0WG0ZQ7Mk9QEEY5Y92HZEk3hMuBoVHVdzmDsm1fSqBYQRGDzS9LKpwSkjLd8tYaRslR7L4gdTF1qyFbpHHK7yAY2RcsV%252Fq%252FKOkEqBpXay86vRVIMLVmioJY7sh7fecBkGrLGZ7FAXSjWzTjv0UbhiqY2mPHRq1bZIi7jdHVcIuYe2q4yl6cSPnNySHUme0rra95RmYLuaBNvZXt5w4GHYMl%252Bph9szyAYZpVFf8OzEtfD8QfNqHdd%7Campid%3APL_CLK%7Cclp%3A2047675
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I bought a coated flat 8inch made by Diane Lucas plus a bunch of 3 a guy made with the 3 disk method who polished but never finished and a number of elliptical secondaries and some smaller ones I suspect are flats too.
Now I have to try to test them to determine what the tolerance of them.
There is a learning curve but I'm sure the reason most ATM have trouble with this test is in getting collimation of the flat with water. I use a laser in my setups and video but it's not perfect and I can be off enough to where the fringes can't be seen, (they are actually there but spaced so close that you can't see them unless you actually get down close and use a magnifier due to too much tilt). So if you really can't get a laser to work you can make an autocollimator using a cheap dime store refractor (there were about a half dozen locally on Craig's list under $25) putting a LED source in a low power eyepiece. The tripod and mount are good for aiming straight down too. Fine pitch leveling screws are very helpful too.
As far as the light source a neon lamp has a bunch of emission lines but I've used one as did Texereau but I can't compare it to a mercury lamp. I use a F4T5 BL (black light) which can be found on Ebay but the fixtures are harder to find. I use Kitchen and Bath fluorescent lamps where I need to do contact testing, they seem to be the best fluorescents. LEDs don't work BTW.
I would advise learning on a small uncoated flat where finding a small lens for a collimator isn't hard. When that's mastered then try a coated mirror and cerium oxide to cut down the intensity. Measuring the water thickness is important as well, 1 mm is good for large mirrors perhaps less for smaller optics.
I haven't tried glycerine but it's higher viscosity would cause either a thicker level or a very long wait for leveling plus a lower reflectivity due to a higher refractive index closer to glass.
Great Video. Thanks for posting. I was not able to hear where the fresnel lens cam from. Could you give me that information again? Thank you and best regards, Francis J. O'Reilly
He said it came from a rear-projection TV, and that he cut it down to size.
No I never tried glycerine but I did find out that the refractive index of pyrex and glycerine are almost identical. Unless you tested an aluminized mirror you wouldn't see any fringes!
Ed
I have a 60 mm +1 dioptry (1 m focal lenght ) lens, but the optical center is offset. Does it matter for making the test ???
That's not a very big lens but if it puts out parallel light it will work.
You tried to use glycerine? Vibrate less, am I right?
Can you use a defocused laser diode as your monochromatic light source?
Well all lasers will have annoying speckle, mercury sources work better.
You sometimes find Fresnel lenses like this one on Ebay 360 dia. X 900 FL:www.ebay.com/itm/184044724952?_trkparms=amclksrc%3DITM%26aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D234205%26meid%3D211a999515454ed9b01fef9224701ee3%26pid%3D101195%26rk%3D1%26rkt%3D12%26sd%3D263133862803%26itm%3D184044724952%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv9PairwiseWithPLXWeb%26brand%3DUnbranded&_trksid=p2047675.c101195.m1851&amdata=cksum%3A184044724952211a999515454ed9b01fef9224701ee3%7Cenc%3AAQAGAAACAMoYPKgvuVfeKcYviaxs%252BPjyVNVrp31VE6oWAL40ib5fKrKwsgEpXt13eTpqf8TglYPvGm3U8x85fAXKlk0DRdSzW4el%252FyzQnMCuHJHBflSHLtc8B6HX%252Bz4JRSJsGRz%252BuHp1k4Db4owFouuaw2ejfpRXnaPqEpeRWDtpFws6Dhu8rZu0h4F8R8OqNSw1etM2aEcLnS8d1P2YQiQj7K%252F5%252BUG9kBVcvkl9Kks2xPRtYbvWSKjJENLX3WIRIl7BJuaizTDJ1IBrh9EBFi8Ev6CPtiOmAucy30BB5uApvGzA%252BWGgHSY%252BX04IuKNa21k074bTE0DeDqg0Hc%252ByMzQfMsiF5Yqujw2yq5ONqCYUaLcIaad12gqMOCT0lWdQRwp1MRahX836yTbpA8wRvkCfaGE8AfmZ70lFY9r97Mu6yTSnn06Qgmi8OmcLtPqF0WG0ZQ7Mk9QEEY5Y92HZEk3hMuBoVHVdzmDsm1fSqBYQRGDzS9LKpwSkjLd8tYaRslR7L4gdTF1qyFbpHHK7yAY2RcsV%252Fq%252FKOkEqBpXay86vRVIMLVmioJY7sh7fecBkGrLGZ7FAXSjWzTjv0UbhiqY2mPHRq1bZIi7jdHVcIuYe2q4yl6cSPnNySHUme0rra95RmYLuaBNvZXt5w4GHYMl%252Bph9szyAYZpVFf8OzEtfD8QfNqHdd%7Campid%3APL_CLK%7Cclp%3A2047675
they can be found for free when someone scraps a rear projection tv for the metals inside.
The voice, hipnotically boring.