This will be the final post on the Sony Alpha full-frame sensor / anti-shake quandary. The first in the series outlined the full frame with anti-shake problem, while the second consisted principally of remarks by Bert Pasquale, a well-respected optical engineer.
Since several readers are sill somewhat confused, I have created some illustrations to help explain the situation.
Figure one shows the relative sizes of various sensors, They are drawn to the exact size, but since monitors and screen resolutions vary, the sizes may not be correct on your screen. The size of each sensor in relation to each other, however, is accurate.
Figure 1: Sensor sizes compared
The red rectangle represents a “full-frame” 24x36mm sensor. The green rectangle is a 17x2mm APSC sensor. The blue rectangle is 90% of a full frame.
Figure 2 shows the APS-C sensor overlaid on a circle that represents the minimum coverage of a 35mm full-frame lens. As you can see, there is plenty of “wasted coverage” as only the area inside the green rectangle will be captured. It is obvious that the sensor can move freely in any direction and still be covered by the lens.
Figure 2: Coverage of a APS-C sensor by a full-frame lens
Figure 3 is a full frame sensor contained inside the exact same coverage circle. There is no established size for the coverage area, as lenses will vary slightly. The designers only have to create a lens that will offer adequate coverage and sharpness of the 24x36mm film area, and still fit within the lens mount. Of course, the greater the lens coverage, the larger and heavier it will need to be. It will probably be more costly as well, so typically lens designers try to keep near the minimum dimension.
As Mr. Pasquale mentioned, the circle of coverage doesn’t immediately fall off to nothing. Rather, the edge of the circle gradually starts to provide lens light and become less sharp.The fall-off increases slowly until the image eventually fades away.
As you can see from Figure 3, there is little room for the sensor to move without clipping at least one of the corners. Again this will vary from lens to lens, as well as with different focal lengths of a zoom lens.
Figure 3: Coverage of a full-frame sensor by a full-frame lens
Figure 4 is an arbitrary 90% sensor. You can see that such a sensor is much larger than the APS-C size, yet still has room to float inside the coverage area. I chose this because several people “in the know” have suggested they believe this will be Sony’s answer to the problem. However, some other authorities have suggested that Sony may opt for a 1.25 crop sensor.
Figure 4: Coverage of a 1.1 crop sensor by a full-frame lens
On the other hand, Mr. Pasquale has suggested that the sensor may not actually move sufficiently enough to require a “crop” lens of any sort. That would be ideal, but until Sony announces the sensor, we really won’t know.
The final figure is one suggested by Alphatracks readers Warren Massey and LEdgars. In their comments, they suggest Sony could simply build an oversize sensor. As you can see by the rectangular outline in figure 5, such a sensor can move some distance in any direction without clipping. The idea is that the big sensor can move around and the camera can crop to a 24X36mm dimension at exposure. it’s a novel idea — but I not sure we will see it in the near future.
Figure 5: Coverage of a oversize sensor by a full-frame lens
First off, it would be expensive. As sensors increase in physical size, the manufacturing yield is less because typically there are more rejects. Even more significant however, is that an oversize sensor would most likely be confined to the Sony flagship. A full-frame sensor would be attractive to many other dSLR makers and in the past, Sony’s sensor division has profited by selling sensors to a wide range of camera makers. Would Nikon have any interest in an oversize sensor? It’s rather doubtful. Nikon uses a lens based image stabilization method, so there wouldn’t be a need for an oversize sensor.
So if Sony does produce an oversize sensor, their principal customer would be Sony — and for the time being only for the top-of-the -line, limited-production flagship. Would that justify designing and manufacturing an oversize sensor? Or would Sony prefer to invest their resources in a sensor they could sell by the truckload to other camera makers as well as their own dSLR division?
Time will tell, but I’m guessing Sony has a plan up their sleeves. It should be quite interesting!
5 Comments
Hmmm… many of the wide angle lenses that sony makes are designed for APS-C sized sensors to begin with – and dont work on my maxum 9 – does that mean they limit the image stabilization because they dont give full coverage to where the CCD could move???
The oversize sensor doesn’t make any sense. The 24×36 crop would always have to be in the place to avoid clipping thus defeating the purpose.
The full frame issue:
In general: With wideangle lenses the image circle is small and the sensor coverage fits this tightly, but only small movements of the sensor are required to compensate. For telephoto lenses, big sensor movements are required but the image circle is also much larger.
I think at worst, a little softening at the extreme corners will occur but nothing to lose sleep over.
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