Some day I hope to invest in the Sony 135 mm f/2.8 STF. Now THERE is a bokeh machine![a href=\"index.php?act=findpost&pid=188852\"][{POST_SNAPBACK}][/a]
That's right. The Minolta/Sony 135 mm STF is the lens with the world's best bokeh ever. It uses a built-in and cleverly designed apodization filter to force the circles of confusion into the shape that naturally leads to perfect bokeh. However it comes at a price: even though the geometric lens speed is 1:2.8, the effective speed is only 1:4.5 due to the transmission loss in the apodization filter. So the lens is f/2.8; T/4.5. And it is manual-focus only even though it's made for Minolta A mount/Sony Alpha mount.
The Nikon DC lenses ('De-focus Control') try another approach to optimize bokeh. They allow the user to adjust spherical aberration through the range from slight under-correction to slight over-correction. So depending on the setting, the DC lenses will get optimized either for background bokeh or for foreground bokeh---but not both, unlike the STF. Also unlike the STF, they don't suffer from transmission losses.
As a side note, if IS has anything to do with the double line effect at all, then doesn't that make the Sony and Pentax sensor shift technology BETTER in this regard? The same effect should NOT happen with sensor shift ...[a href=\"index.php?act=findpost&pid=188852\"][{POST_SNAPBACK}][/a]
No. As I already said in my previous post, the problem is the same no matter whether the image stabilizier is built into the lens (moving lens elements) or into the body (moving sensor).
Update: I just fired a few frames, to test if the image stabilizer really affects bokeh to a perceptable degree. I used a Konica-Minolta Dynax 7D (APS-C format, 6 MP, in-body image stabilizer) and a 560 mm 1:6.3 lens (Minolta AF Apo 400 mm 1:4.5 G with 1.4× TC). The focus distance was approx. 35 m/100 ft; the background had many sharp edges and specular highlights (cars in a parking lot) and was approx. 100 - 120 m/330 - 400 ft away. I tried f/6.3 at 1/500 s and f/16 at 1/80 s. For the hand-held shots, I was wielding the camera up and down vigorously, to give the stabilizer a real work-out. Still nearly all shots are sharp, even those taken at 1/80 s. For the tripod shots, I switched the stabilizer off. Result: ummm. At first sight: no difference. At a closer look: the hand-held shots show a tendency for harsher bokeh and hints of double lines, and the tripod shots don't ... but that's at the borderline of perceptability; it takes a
very close look to notice. So I guess it will take a few more tests to settle this issue, using different combinations of focal lengths, apertures, shutter speeds, focus distances, and background distances.
-- Olaf