Archived posting to the Leica Users Group, 2000/02/14
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Pitak, the simplest testchart for lenses is a double spread of classified ads, mounted flat on a board (white glue is fine) and hang on a shaded wall, not direct sunlight and avoid tungsten light, unless you shoot everything under that condition. Be careful and align the camera/lens and the testchart so that the Leotaxes is at 90 degrees to the chart. I use Post-It notes and write the lens. f-stop and speed on it and stick it on the chart. Shoot with fine grain black/white (APX 25/Pan-F+/tech-pan) and develop in a 'sharp" developer (Rodinal, FX-37 or something like that). Get a good printers loupe with 20x magnification for checking edges and center sharpness. Use the same body for all the lenses as this puts all the lenses on equal footing as to shutterspeed, body tolerances etc. Heavy tripod is a must, even a solid floor is critical — it is surprising how much vibration can be generated by somebody walking by! Of course, all of this is only meaningful if you make your living shooting pages of classified ads, but is can sure while away an afternoon! Always go through the whole gamut of apertures, you might be surprised to find big, visible differences between the extremes of the f-stops. Also do some test by measuring the exact distance between the testchart and the cameras filmplane. Set the lens to the indicated measurement and shot a couple of shots, then focus with the groundglass or rangefinder and see if there is a difference. I used to do this with every new lens and body but now I only do it if I feel there is a problem. Tom A