Category Archives: technology

Lens design

As someone who has had a metric tonne load of problems in seeing clearly, I’ve become quite interested in lens design.

There’s a great course on Opticampus that explains the rationale behind and mathematics of spectacles lens design.  Lens design is a trade-off between the minimisation of different forms of aberrations brought about by practical considerations such as the shape of the lens, the quality of the material and the prescription that must be glazed.

Lens designers measure differences in refraction across tangential and sagittal meridians (orthogonal meridians describing refraction of light at different degrees from the optical centre of the lens).  They must minimise the oblique astigmatism which is the difference in refractive power between the 2. A good way to describe this is that light may be bent more vertically than horizontal leading to a squatter image or vice versa.

They must also compensate for power error which arises from the focal point of a perfect lens as light hits it from its range of lateral and vertical points of incidence   (theoretical and ignoring oblique astigmatism) being different from the Focal Point Sphere which represents the back surface of the eye.  The FPS is generally more curved and hence the lens may focus behind the eye away from the optical centre.

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Predicting a rotten Apple

Business Insider writes

“Apple is set to release iPhone 6, its latest update to the iPhone juggernaut, in the fall. While iPhone 6 sales are expected to be huge for various reasons, there is a broader question facing Apple: Is it boxed in as a brand and a platform that merely serves the richest 15% of the world, while everyone else uses Android?”

Madness. Nobody questions the sense in marketing a premium product to the same people who buy BMW’s , Mercedes & Audi but that’s a smaller % of the near $90Bn unit global car market than the iPhone is of the global phone market.  Nothing wrong with marketing to the richest 15% in the world, in a purely commercial sense anyway.

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Pulse Width Modulation & Eyestrain

In my last post I mentioned problems with PWM-dimmed monitors as an aside but that’s not an accurate reflection of the negative effects I think PWM can have on some people.

Pulse Width Modulation dimming involves varying the frequency of the LED backlight pulse to give the impression that the monitor is less bright. TFT central explain the technique here

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