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

Started Jun 16, 2014 | Discussions thread
stevo23 Forum Pro • Posts: 17,844
Re: How curved?

alanr0 wrote:

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.

You have no idea what the curvature is yet. I don't believe the sensor will have a simple curve.

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

I'm not sure why. You have no idea what the exit angle of the light "rays" are and you have no idea what the curvature of the lens element or the sensor are.

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 lot of assumptions, no facts yet to back it up.

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.

Facts - that's what we need. What is the curvature of existing lenses? For sure they vary quite a bit. You have no idea, you're only speculating. You could be right, but this is only speculation.

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.

I don't really see any plausible science to back that up. We would need to know what the curvature of existing lenses is and then the change in angle of incidence at various places on the sensor to know how this differs from today in terms of performance.

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