Sony's new curved sensor - this is a big deal

Started Jun 16, 2014 | Discussions thread
alanr0 Senior Member • Posts: 2,094
Re: How curved?

stevo23 wrote:

alanr0 wrote:

Alternatively, if the figure above is to scale (which it may not be), the sensor height at the edge of the field is about 2.6 mm.

I thought you might be doing this. Probably not worth making this assumption.

With a conventional flat field f/1.8 lens focused at the centre of the field, the diameter of the circle of confusion at the edge of the sensor will be (2.6 mm / 1.8) = 1.4 mm.

Even with this lower curvature estimate, it would be completely impractical to use a conventional lens with such a strongly curved sensor. For an 'acceptable' circle of confusion of 0.036 mm, only a small central area of less than 3 mm radius will be in focus.

You're making a lot of assumptions here that probably can't be made just yet.

How about starting with some facts.

At f/1.8, the centre of the sensor is illuminated by a cone of half-angle 15 degrees.  For the curvature of the sensor to make even a small difference to the sensor efficiency, the tilt at the edge must be at least 5 degrees.  For uniform spherical curvature, that would lift the sensor edge is 0.8 mm above the centre.

If the curvature is much less than this, then the "improved efficiency at the edge" claim fails.

If the curvature is as large as this, the sensor will be useless with existing lenses.  For example the Pentax FA 50 mm f1.4 is rather soft wide open, but still resolves 800 line widths/picture height across the frame at f/2.  For a generous circle of confusion of 16/800 = 0.02 mm the focus error at the sensor must be less than 0.04 mm at f/2.

A reasonable conclusion is that existing large aperture lenses of moderate quality or better have a field which is flat to much better than 0.1 mm, and probably less than 0.05 mm.

If the curvature is low enough to be useful with existing lenses, there is no advantage in terms of vignetting, and minimal advantage in terms of lens design.

Joseph Wisniewski knows something about lens design, and has an entirely plausible explanation.


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Alan Robinson

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