giordano Posted January 25, 2011 Share #101 Posted January 25, 2011 Advertisement (gone after registration) I have completed my measurements of the base curves of the front and back lens on the new SX35 FLE. I have chosen to represent the radius of curvature translated to its dioptric power. <snip> Front: -10.50 Back -20.00 Thank you for taking the trouble. But don't you need to tell us the refraction index as well as the dioptric power if we are to be able to work out what the radius is? Link to post Share on other sites More sharing options...
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Xmas Posted January 25, 2011 Share #102 Posted January 25, 2011 Thank you for taking the trouble. But don't you need to tell us the refraction index as well as the dioptric power if we are to be able to work out what the radius is? Not if that is the power is as a mirror... he will have ysed a laser pen? Noel Link to post Share on other sites More sharing options...
Rick Posted January 26, 2011 Share #103 Posted January 26, 2011 Thank you for taking the trouble. But don't you need to tell us the refraction index as well as the dioptric power if we are to be able to work out what the radius is? Not exactly. The radius of curvature of a lens is described in optics often as just the reciprical of the dioptric. The power (in diopters) of the lens is described as; Power(in diopters) = (n − 1)C. Where n=the refractive index and C=the r of curvature. Why, I said not exactly, is for two reasons. The measurement I gave was a physical measurement of the curvature, that I physically measured (as apposed to calculated). The instrument I used to measure the radius of the front surface reads out in diopters and assumes that the inverse of the radius (in meters) is the dioptric measurement of the curvature. We assume this because, light has not passed through the lens so, we can assume the simple inverse law. Had I measured the lens' "power" in diopters, I would have to know the index of the glass. And, I'd have to know at least one of the following; the vergence of light passed through the lens or the back radius. So, I just kept it simple and described the radius of the front curve in diopters. The second reason that I did it this way is because, my name is not Mark. I didn't want to take my lens apart and measure the vergence of light exiting the front lens (which means breaking apart the element) and then, measure the curvature of both surfaces, only to then, calculate the index of refraction of the lens when, all I really want to know is if the front lens is different in it's front curvature (the only metric anybody is going to realistically be able to measure) from the old lens. Link to post Share on other sites More sharing options...
masjah Posted January 26, 2011 Share #104 Posted January 26, 2011 Rick My hazy recollection of my 37 year old A-level Physics tells me (possibly my recollection is very hazy though) that P = 1/f = (n - 1)[1/R1 + 1/R2] = (n - 1)[C1 + C2]. Here f is the focal length, R1 and R2 are the two radii of curvature (but note that the curvature C is the reciprocal of the radius of curvature) and P is the power (in dioptres, if the units of measurement are in metres). I would have thought then that your formula is appropiate for a lens with one plane surface. This formula is based on linearised, thin lens theory, so is not exact for a "real life" lens. Link to post Share on other sites More sharing options...
giordano Posted January 26, 2011 Share #105 Posted January 26, 2011 So: radius of front surface 95.24mm; back surface 50.00mm. Link to post Share on other sites More sharing options...
Xmas Posted January 26, 2011 Share #106 Posted January 26, 2011 So: radius of front surface 95.24mm; back surface 50.00mm. 5cm seems very short for a f1.4 lensis that he aspherical? Link to post Share on other sites More sharing options...
Rick Posted January 26, 2011 Share #107 Posted January 26, 2011 Advertisement (gone after registration) Rick My hazy recollection of my 37 year old A-level Physics tells me (possibly my recollection is very hazy though) that P = 1/f = (n - 1)[1/R1 + 1/R2] = (n - 1)[C1 + C2]. Here f is the focal length, R1 and R2 are the two radii of curvature (but note that the curvature C is the reciprocal of the radius of curvature) and P is the power (in dioptres, if the units of measurement are in metres). I would have thought then that your formula is appropiate for a lens with one plane surface. This formula is based on linearised, thin lens theory, so is not exact for a "real life" lens. You are correct, good memory. I used only one surface because, I wasn't interested in calculating the "power" of the lens, only the dioptric equivalent of the front surface. I did this at work and didn't bother converting it to radius of curvature because my little instrument reads out dioptric equivalents. I figured that anyone else doing the same for the old lens would probably measure the front surface in the same way I did, so why bother converting. And, giordano did it anyway. Xmas, note that the "back surface" that masjay refers to is the back surface of the back lens. Not the back surface of the front lens. Anyway, maybe someone else can measure their old lens. Link to post Share on other sites More sharing options...
Xmas Posted January 26, 2011 Share #108 Posted January 26, 2011 You are correct, good memory. I used only one surface because, I wasn't interested in calculating the "power" of the lens, only the dioptric equivalent of the front surface. I did this at work and didn't bother converting it to radius of curvature because my little instrument reads out dioptric equivalents. I figured that anyone else doing the same for the old lens would probably measure the front surface in the same way I did, so why bother converting. And, giordano did it anyway. Xmas, note that the "back surface" that masjay refers to is the back surface of the back lens. Not the back surface of the front lens. Anyway, maybe someone else can measure their old lens. Hi RickLeica I understood that I was panicing cause subjectively it seemed like a lot of power given high refractive index glass, but Ive camed down now. I looked at the technical information and both surfaces are concave, dont need my slide rule to be happy. Did anyone make a copy of the technical information for the older version? Noel Link to post Share on other sites More sharing options...
masjah Posted January 26, 2011 Share #109 Posted January 26, 2011 You are correct, good memory. I used only one surface because, I wasn't interested in calculating the "power" of the lens, only the dioptric equivalent of the front surface. I did this at work and didn't bother converting it to radius of curvature because my little instrument reads out dioptric equivalents. I figured that anyone else doing the same for the old lens would probably measure the front surface in the same way I did, so why bother converting. And, giordano did it anyway. Xmas, note that the "back surface" that masjay refers to is the back surface of the back lens. Not the back surface of the front lens. Anyway, maybe someone else can measure their old lens. Thanks Rick. I wouldn't care to use that formula on a compound lens, simply taking the radius of the front surface and the radius of the back surface, since, as I mentioned earlier, it is derived on the basis that we are talking about a single element (meniscus). Link to post Share on other sites More sharing options...
GlobeRiders Posted February 4, 2011 Share #110 Posted February 4, 2011 Hi I had the previous version for many years and enjoyed that lens except the focus shift issue. Lost confidence in it and "upgraded" to the latest version. Not cheep upgrade, but very happy with the results. Unfortunately this lens fell apart on a journey to Africa last fall. Front lens element came loose and the diaphragm blades were floating loose inside the lens. Very sad when this happens in middle of a 2 1/2 months journey in Africa. M9 and my new 50mm Lux and 21mm Elmarit did just fine. No problems with my Canon Eos system either. Sent lens to Leica end of 2010 and first estimate for repair was 1/17/11, never came so I called and are now told new date to be around 2/18/11. Anyone else had mechanical problems with this lens? Thanks. Helge Pedersen Link to post Share on other sites More sharing options...
kkochheiser Posted February 5, 2011 Share #111 Posted February 5, 2011 Hi Helge, Out of curiosity, was the lens on the camera when it came apart? And was it on the BMW with you at the time? I haven't had a chance to take my M9 rig with me on my GS yet and now I'm a little worried since I know from the Globe Riders videos how well you pack your gear. Thanks, Kent Link to post Share on other sites More sharing options...
GlobeRiders Posted February 5, 2011 Share #112 Posted February 5, 2011 Kent and All All of my photography equipment is always on my motorcycle or in a waterproof fanny bag hanging around my waist. Without to much details to how this works, my point is that I have used the same system for years and the only serious problems I have had have been with my Leica equipment. Leica M8 died in the middle of a tour, 28mm new Elmarit came apart and now lately the 35 Lux fell appart. Non of this due to any accident or abuse different from the rest of the equipment. Again, all I can say is that I carry a lot of equipment and it is all treated the same way with the best care I can give it. The 35mm Lux on the M9 is my favorite lens to work with. After having problems with the focus shift on the previous version of the 35 Lux I noticed that I lost my excitement of using the M9. Getting the new 35 Lux got me back on track again and I carry the M9 w/35 Lux everywhere. I always bring along the new 50 Lux and 21 Elmarit, but the new 35 Lux is my new baby. Can't wait to get her back. Thanks. Helge Pedersen Link to post Share on other sites More sharing options...
Xmas Posted February 5, 2011 Share #113 Posted February 5, 2011 Hi People say that if you don't handle the 28mm Elmarit Asph by mounting and unmounting it using the correct ring (i.e. the inner most) it will dismantle... Noel Link to post Share on other sites More sharing options...
lct Posted February 5, 2011 Share #114 Posted February 5, 2011 What do you mean by dismantle? Is the lenshead unscrewing when you hold it by the square hood like the 35/2 IV? Link to post Share on other sites More sharing options...
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