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| p.8 #6 · Metabones Speed Booster |
Looking at the optical traces of the adapter, it follows all conventional rules for non-anomalous dispersion glass. That is, it has the same polarity of errors as any normal photographic lens would have.
This means from the image's point of view that any normal aberration in a lens will be worse, not better. The SIZE in µm of the aberration might be smaller, but the size in part of image width will be larger.
So, even if an aberration shrinks by a factor of 1.3 (13µm displacement >>> 10µm displacement) which seems about right when looking at their published MTF over image height, that aberration then needs to be enlarged by 1.5x to get the same image.
Lets say you have two 10MP cameras, one FF and one APS. That's about 4000 pixels image width, same for both. Their pixel sizes will be 9µm and 6µm respectively, to get 10MP.
If you have an aberration that's 13µm on the FF camera, that's the same as 1.44 pixels in the image.
That same aberration will be 13/1.3 = 10µm on the APS camera (with adapter). 10µm/6µm pixels = 1.67pixels.
So even if the aberration is smaller, the impact on the actual image is larger. 1.67 pixel widths versus 1.44 pixel widths in the original.
Giving it some thought since yesterday, I've slightly changed my mind though. About the value of the adapter...
For people accepting manual focus as something a part of normal photography, this is well spent money. With the improvements in ergonomics with the latest NEX cameras (also µFT) this might actually improve a lot of things.
What you get:
More field of view per focal length (good, shorter focal lengths are often worse for adapted lenses)
Higher aperture value on the adapted lens to get "the same image" - this in itself is the most important part!
Slightly (7mm?) shorter overall camera/lens package than using same lens with normal adapter (though you'll need a longer FL lens to get the same image)
One of my main reasons for using larger format systems is that the image quality per DoF (at shallow DoF's) in a real image increases almost exponentially. My 130€ AFS50/1.8 @ F2.8 ISO400 on my D800 literally walks all over the 700€ Zeiss 35mm @F2.0 ISO200 on a NEX camera. If just a little bit of that disadvantage disappears, priorities might change - considering the size difference of the packages.