Fixtureless lensmeter and methods of operating same

1. A method for determining characteristics of a lens, the method comprising:

capturing a first captured image of a pattern through a corrective lens while the corrective lens is at a first distance from the pattern;

capturing a second captured image of the pattern through the corrective lens while the corrective lens is at a second distance from the pattern;

processing the first captured image to determine a first spherical power measurement;

processing the second captured image to determine a second spherical power measurement;

selecting, from among a plurality of spherical power measurements comprising the first spherical power measurement and the second spherical power measurement, either the first spherical power measurement or the second spherical power measurement as an extreme spherical power measurement; and

determining, with reference to the extreme spherical power measurement, a lens power of the corrective lens.

2. The method of claim 1 , wherein the extreme spherical power measurement is the largest absolute value among the plurality of spherical power measurements where the corrective lens is a converging lens, and wherein the extreme spherical power measurement is the smallest absolute value among the plurality of spherical power measurements where the corrective lens is a diverging lens.

3. The method of claim 1 ,

wherein processing the first captured image to determine the first spherical power measurement comprises transforming the first captured image to an ideal coordinate system, and

wherein processing the second captured image to determine the second spherical power measurement comprises transforming the second captured image to the ideal coordinate system.

4. The method of claim 3 , wherein transforming the first captured image to the ideal coordinate system comprises:

detecting a plurality of captured reference landmarks in a second region of the first captured image;

determining a transformation from a plurality of ideal reference landmarks to the plurality of captured reference landmarks; and

applying the transformation to the first captured image.

5. The method of claim 1 , wherein processing the first captured image to determine the first spherical power measurement comprises:

determining an overall distortion from a reference pattern to the pattern of the first captured image; and

determining a distortion of the pattern of the first capture image attributable to the corrective lens.

6. The method of claim 5 ,

wherein the first captured image is captured by a camera having a camera lens, and

wherein determining the distortion of the pattern of the first captured image attributable to the corrective lens comprises:

determining a distance between the camera lens and the pattern; and

determining at least one focal length of the corrective lens with reference to the distance and the spherical power measurement.

7. The method of claim 1 , wherein processing the first captured image to determine the first spherical power measurement comprises:

detecting, in the first captured image, a plurality of captured pattern landmarks;

determining a transformation from a plurality of ideal pattern landmarks to the plurality of captured pattern landmarks; and

determining for the corrective lens, from the transformation, the first spherical power measurement.

8. The method of claim 7 , further comprising determining for the corrective lens, from the transformation, a cylinder power measurement and an astigmatism angle measurement.

9. The method of claim 7 , wherein the transformation is a dioptric power matrix.

10. The method of claim 1 ,

wherein each of the first captured image and the second captured image includes a first region containing the pattern and created by light passing through the corrective lens, and a second region created by light not passing through the corrective lens, and wherein determining a distortion of the pattern of the first captured image attributable to the corrective lens is performed at least in part with reference to the second region.

11. The method of claim 10 , wherein the pattern comprises a checkerboard pattern, and wherein the second region contains a border.

12. The method of claim 1 ,

wherein the first captured image and the second captured image are captured by a camera having a camera lens, and

wherein the camera lens is positioned at a fixed distance from the pattern during capture of the first captured image and the second captured image.

13. The method of claim 1 , further comprising determining a prescription of the corrective lens, the prescription including at least a sphere value, a cylinder value, and an axis value.

14. The method of claim 1 , further comprising:

determining, from the first captured image, a first distance from a camera lens of a lensmeter with which the first captured image was captured to the pattern;

identifying a direction to a second location relative to a first location;

guiding a user of the lensmeter to the second location; and

capturing the second captured image of the pattern through the corrective lens at the second location.

15. The method of claim 14 , further comprising:

guiding the user of the lensmeter from the first location to a third location to the second location; and

capturing a third captured image of the pattern through the corrective lens at the third location, wherein the third location is substantially halfway between the lensmeter and the pattern.

16. The method of claim 1 ,

wherein the pattern is a first pattern and the corrective lens is a first corrective lens, and

wherein capturing the first captured image further comprises capturing, in the first captured image, a second pattern through a second corrective lens,

wherein the first pattern and the second pattern are spaced from each other such that the first pattern and the second pattern are able to be captured in the first captured image when the first corrective lens and the second corrective lens are positioned at a known location relative to the first pattern and second pattern.

17. A lensmeter comprising:

a camera having a camera lens;

a visual display; and

a processor coupled to the camera, the processor configured to:

capture a first captured image of a pattern through a corrective lens while the corrective lens is at a first distance from the pattern;

capture a second captured image of the pattern through the corrective lens while the corrective lens is at a second distance from the pattern;

process the first captured image to determine a first spherical power measurement;

process the second captured image to determine a second spherical power measurement;

select, from among a plurality of spherical power measurements comprising the first spherical power measurement and the second spherical power measurement, either the first spherical power measurement or the second spherical power measurement as an extreme spherical power measurement; and

determine, with reference to the extreme spherical power measurement, a lens power of the corrective lens.

18. The lensmeter of claim 17 ,

wherein the extreme spherical power measurement is the largest absolute value among the plurality of spherical power measurements where the corrective lens is a converging lens, and

wherein the extreme spherical power measurement is the smallest absolute value among the plurality of spherical power measurements where the corrective lens is a diverging lens.

19. The lensmeter of claim 17 , wherein each of the first captured image and the second captured image includes a first region containing the pattern and created by light passing through the corrective lens, and a second region created by light not passing through the corrective lens.

20. A method for determining characteristics of a lens, the method comprising:

obtaining a plurality of captured images of a pattern through a corrective lens while the corrective lens is moved relative to the pattern;

processing each captured image of the plurality of captured images to determine a plurality of spherical power measurements, each of the plurality of spherical power measurements determined from one of the plurality of captured images;

selecting an extreme spherical power measurement from among the plurality of spherical power measurements; and

determining, with reference to the extreme spherical power measurement, a lens power of the corrective lens; displaying, storing, or transmitting the determined lens power of the corrective lens.