Method of measuring optical properties of a transparency

Abstract

A method of measuring optical properties of a transparency uses a video camera for focusing and then refocusing an image of a point source of light transmitted through a test region when the transparency is first absent and then later present at the test region. The distance the camera needs to be moved together with the focal length of a focusing lens used in carrying out the method provide sufficient quantitative data to calculate the spherical optical power of the transparency. Also, the camera generates video images of the point source both before and after the transparency is present in the test region. These images are displayed on a screen containing a grid pattern which facilitates measurement of the displacement of the image from the center of the grid or from the optical axis due to the presence of prismatic deviation in the transparency. Given the earlier data and supplemented by the latter displacement quantity, the prismatic deviation of the transpareny can also be calculated.

Having thus described the invention, what is claimed is: 
     
       1. A method of measuring spherical optical power of a transparency, comprising the steps of: (a) providing a substantially point source of light;   (b) collimating light from said source and projecting the light so collimated along an optical axis from said source through a test region defined along said axis;   (c) receiving collimated light at a predetermined first location along said optical axis after the collimated light passes through said test region and focusing said collimated light to produce a first point image of said source at a first distance "f L  " from said first location, and measuring "f L  ";   (d) disposing a video camera at a first position along said optical axis and focusing said camera on said first point image;   (e) placing a transparency within said test region and along said optical axis at a second location between said source and said first location, said second location being displaced from said first location by a predetermined distance "d";   (f) receiving collimated light at said first location along said optical axis after the collimated light passes through said transparency and test region and producing a second point image of said source;   (g) moving said video camera along said optical axis to a second position and focusing said camera on said second point image;   (h) measuring the distance "R" between said first position and said second position of said video camera; and   (i) calculating the spherical optical power of said transparency by solving for φ v  where ##EQU6##   
     
     
       2. The spherical optical power measuring method as recited in claim 1, wherein said second location is selected to define d to be small compared to f L  whereby the ratio d/f L  is substantially negligible, and the spherical optical power of said transparency φ v  is calculated using the relationship, ##EQU7## 
     
     
       3. A method of measuring prismatic deviation of a transparency, comprising the steps of: (a) providing a substantially point source of light;   (b) collimating light from said source and projecting the light so collimated along an optical axis from said source through a test region defined along said axis;   (c) receiving collimated light at a predetermined first location along said optical axis after the collimated light passes through said test region and focusing said collimated light to produce a first point image of said source at a first distance "f L  " from said first location, and measuring "f L  ";   (d) disposing a video camera at a first position along said optical axis and focusing said camera on said first point image and generating a first video image of said first point image;   (e) displaying said first video image on a screen at a preselected position on a grid pattern contained on said screen;   (f) placing a transparency within said test region and along said optical axis at a second location between said source and said first location, said second location being displaced from said first location by a predetermined distance "d";   (g) receiving collimated light at said first location along said optical axis after the collimated light passes through said transparency and test region and producing a second point image of said source;   (h) moving said video camera along said optical axis to a second position and focusing said camera on said second point image and generating a second video image of said second point image;   (i) displaying said second video image on said grid pattern contained on said screen;   (j) measuring the distance "R" between said first position and said second position of said video camera;   (k) measuring the distance "S" between said first and second video images as displayed on said grid pattern on said screen; and   (l) calculating the prismatic deviation of said transparency by solving for O p , where ##EQU8##   
     
     
       4. The prismatic deviation measuring method as recited in claim 3, further comprising the step of: calculating the spherical optical power of said transparency by solving for φ v , where ##EQU9##   
     
     
       5. The prismatic deviation measuring method as recited in claim 3, wherein said second location is selected to define d to be small compared to f L  whereby the ratio d/f L  is substantially negligible, and further comprising the step of: calculating the spherical optical power of said transparency by solving for φ v , where ##EQU10##