#225. Why Sony’s Curved-Sensor RX2 is Excellent News for the Travel Photographer

By pascaljappy | Opinion

May 13

It’s been over 18 months since the website Egami discussed Sony’s curved-sensor patent. More recently, Andrea, of Sony Alpha Rumours added to the intrigue by mentioning a second patent for a dedicated 35mm f/1.8 lens, implanting into our fragile minds that the 2 would combine into a neat RX2 replacement for the already brilliant RX1, possibly as early as this summer!

Tastier and tastier.

Usually, technological advances leave me cold. Higher ISO capabilities won’t change my life. Nor will a faster autofocus or 20% more pixels on my waffle. But I think this potential RX-2 is a big deal for travel photographers.

Here’s a diagram of the sensor. Only the bottom image is interesting. As you can see it’s curved inwards.

(c) Sony Corporation

(c) Sony Corporation

This topology has led to many comments on forums, some asking why go to such lengths when the lenses would obviously have to be that much more complex. Ironic, as while the curved sensor claims many advantages, simpler lens design is the most important to me.

So here are some of the features we can expect from the potential RX2 and how they translate into real life advantages for us users.

Below is a statement made by Sony during a tech symposium:

We realized an ultimately advanced imaging system that comprises a curved, back-illuminated CMOS image sensor (BIS) and integrated lens, which doubles the sensitivity at the edge of the image circle and increases the sensitivity at the center of the image circle by a factor of 1.4 with one-fifth lower dark current than that of a planar BIS.

Because the lens field curvature aberration was overcome in principle by the curved sensor itself, the curved BIS enables higher system sensitivity through design of a brighter lens with a smaller F number than is possible with a planar BIS. At the same time, we controlled the tensile stress of the BIS chip to produce a curved shape that widens the energy band-gap to obtain a lower dark current. The curved CIS can be applied to an ultimately advanced imaging system that is validated by the evolution of the animal eye in Nature.

Advantage 1: higher sensitivity. We can expect half a stop of added sensitivity with lower vignetting.
Advantage 2: lower dark current. This should translate into a (slightly) higher dynamic range, always important outdoors.

Impact on lens design

Here’s where I think the RX2 should particularly shine. The RX1’s Sonnar 35mm f/2 is one the all time great 35mm lenses. There simply isn’t an area of performance you can fault. It’s an absolutely superb lens.

It’s also a complex design (see below. Although this is NOT the Sonnar’s diagram, it’s an equally complex lens, shown here purely for visual comparison to what the RX2 may be using). The RX1’s Sonnar uses the following formula: 8 elements in 7 groups, 3 elements using aspherical surfaces, one of which being an “Advanced Aspherical”, whatever tha means. Such a lens is complex to design, expensive to build and tolerances are very tight.

(c) Sony Corporation

(c) Sony Corporation

And that’s where the curved-sensor works its magic!

Old-timers, particularly those interested in astronomy, know that a single spherical lens naturally focuses on a curves surface rather than a plane. In this diagram by Starizona, you see how that can be a problem for digital cameras.

(c) Starizona, click to access interesting article.

(c) Starizona, click to access interesting article.

This is not limited to telescopes, and many famous lenses (including the superb Leica Summiluxes) have curved focal surfaces. So does your eye (the retina).

In fact, a large part of the complexity of the design of telescopes and camera lenses is due to trying to make the focal surface … plane. A field flattener for an amateur telescope already consists of 3 or 4 lenses. Wide-field telescopes of the film era employed curved film holders on which photographers had to place their cut film, frame by frame. Modern giant scopes use curved arrays of sensors to avoid the design and build of extremely complex correctors.

And the beauty of Sony’s curved sensor is evident when you consider the patent diagram for what could be the RX2’s lens, below.

(c) Sony Corporation

(c) Sony Corporation

Compare this to the first diagram, which serves as realistic proxy for the RX1 lens. A lot simpler, right ?

Benefit 3: Cheaper. Much cheaper, in fact. No specifics are available regarding the number of aspheric surfaces in this design, but I’ll bet it’s lower than in the RX1 lens. Less work, looser tolreances (aspherics need extremely tight mounting tolerances) and fewer lenses all translate to a cheaper lens. Cheap enough to include an EVF for the same retail price?

Benefit 4: Smaller and lighter. Those who objected to the RX1’s relatively large lens should have less to rant about, with the (potential) RX2. And although there is a minimum size to cover the whole field, a smaller front element is probably required than in a flat sensor design to avoid severe vignetting.

The Thames barrier

Thames Barrier – sharp meets soft (c) Pascal Jappy

Benefit 5: Vintage look, modern performance. This is speculation on my part, but the drawing qualities a designer injects into his lens are a matter of compromise. If you read Naoki Miyagawa’s interview by LesNumeriques, you’ll see he is a fan of the C-Sonnar and venerable Jupiter 8. Who knows what a brilliant mind coupled to fewer design constraints can produce ? Can he serve up FE 55 performance with Jupiter 8 (or Noctilux) cream? Yummy!

Curved sensor limitations

Every coin has its flip side. And the sensor’s curvature should only match a very limited range of focal lengths. If the first, fixed lens is indeed the 35mm f/1.8, I don’t see it working with an 18mm (it would need to be much more concave) or a 400mm (it would need to be much flatter).

And, of course, none of the lenses in our precious collections will work.

But that’s a small price to pay, for 2 reasons:

    1. As I have already written, we enter an age of in camera correction of lens aberrations and our precious Leica-M will soon look like dinosaurs. Even with no curved sensor, this is no time for lens collecting.
    2. Stitch 2 frames from the (potential) RX2 and you have yourself a neat 20mm image. I wouldn’t be surprised to see the feature embedded in Sony RX cameras (it’s just an improvement on the existing panoramic feature). Crop to the center 9Mpix (plenty enough for an A3+ print) and you have a very good 70mm lens (and that too is built-in our cameras, it’s called a digital zoom). So there you have it, a 20-70mm zoom. Perfect for travel photography and all someone like Galen Rowell would have required for his fantastic work.

Sony, please don’t make me lie 😉

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  • Philip Partridge says:

    I think Sony have something special just around the corner for us. This curved sensor camera is one possibility, and it could use a higher Mp sensor count to provide flexibility for cropping options – cropping is another huge benefit of very flat field, high performance lenses with low aberrations and even illumination – both issues with traditional M class lenses. Advanced aspherical refers to both sides of an element being fabricated as asph surfaces – the RX1 has 5 such surfaces.

    The other possibility to consider is an RX1-style camera built around the new 44×33 50Mp MF sensor which has very reasonable size pixels for excellent low light work – lens coverage needs are well-constrained by the 4:3 aspect ratio – you need only cover a diameter of 55mm compared with 645 film’s needs of 69mm and 35mm requirements of 43mm. Sony could use a lightly scaled-up CZ Sonnar in a 45mm f2 design (Zeiss has huge experience of MF optical design) with an additional 8mm of body width and 10mm of body height with a small increase in lens-body depth, built-in EVF and total weight of around 650 grams – less than the body alone of a Leica M…such a file would provide 20Mp+ files for most needs – even pano sizes and of course a 24x36mm crop for a 30Mp file – a sweet spot.

    They would sell thousands of these, priced at say $4500, with a large profit margin. The special technology in the RX1 has already been developed as has lens design. Mirrorless cameras with fixed lenses are an exciting development path for Sony for these and other reasons – notably they are at a massive disadvantage against Canon and Nikon regarding established lens lineups. They are being asked by the user base to do for FE in 1-2 years what C/N did over 20-30 years.

    Zeiss is a company that sees innovation and the progression to market of innovative products both as a challenge and as advanced R&D which they can flow down to lower level consumer product. They might relish these design initiatives.

    • pascaljappy says:

      Philip, I certainly hope you are correct. I too would be very interested in a leaf-shutter 4:3 45mm f/2 (even f/2.5) with the current sensor at the price point you mention. I can’t see than happening any time soon, as other manufacturers will probably want to use the sensor without competition from Sony for 18 months. But after that, who knows what can happen.

      Maybe Sony can make the 2 lines converge at some point. A curved sensor MF RX3 in 2016 ? I’m not sure Sony have the long term vision to think in those terms, the positive side of that innovative restlessness being that they might have something even more imaginative on the charts by then 😉

      Thanks for the precision on Advanced Aspherics.

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