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10-20-2010, 06:06 AM   #1
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Defocus (bokeh) control lens for Pentax

I was having a dinner and saw this lens with someone sitting on the next table. Though I couldn't get a chance to operate, I found it very interesting - defocus control - let you control the bokeh. Quick google got me this page with details:

Update: Note that, this is not a soft-focus lens, it's a very sharp lens with ability to control bokeh - more details in link below (refer to defocus control section). So it can not be compared with Pentax soft focus lenses.

Nikon 135mm f/2 DC

Does anything similar exist for we Pentax users.

Yusuf


Last edited by yusuf; 10-20-2010 at 07:59 AM.
10-20-2010, 06:55 AM   #2
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Not exactly, but Pentax does have a number of "Soft" lenses, like a few 85's and a 28 as far as I know. It's usually described as lending a "dreamy" look to photos rather than controlling the amount of bokeh.

Here's one of them:
SMC Pentax-FA 85mm F2.8 Soft Lens Reviews - Pentax Lens Review Database

I believe there were F versions and an SMC (K) f/2.2 version as well.

Here's a thread with some pics:
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/64655-pentax-f...s-samples.html

Again, not quite what the DC lens does, but the closest to that type of thing that Pentax has.

Last edited by farfisa; 10-20-2010 at 07:00 AM.
10-20-2010, 07:56 AM   #3
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This is not a soft focus lens, it's a very sharp lens with ability to control bokeh. Read the link in OP.
10-20-2010, 08:10 AM   #4
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The DC lenses are very cool. Very cool indeed.

10-20-2010, 08:33 AM   #5
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That's on my must-have list of Nikkor's, should I ever move to that brand. And Sony has the 135mm f/2.8 [T4.5] STF.

Nothing like these for Pentax, and if there was I think it would be more than $1200, the way prices are going.
10-20-2010, 12:19 PM   #6
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Nikon's (very good) article on the DC-Nikkors:

Nikon | Imaging Products | NIKKOR - The Thousand and One Nights, Tale 32 : Ai AF DC Nikkor 135 mm f/2S
10-20-2010, 12:48 PM   #7
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although I can't prove it, I suspect that this lens modifies the shape of the aperture blades, or the opening, somehow.

My own pet theory of why preset lenses have better bokeh than modern lenses is a combination of round apertures at all openings, (due to any wher from 12 to 18 sculpted blades) as opposed to hexagonal, pentagonal , etc openings as a result of straight (or nearly so) blades. That plus position make presets have better bokeh.

Now, apply that to nikon's lens. what if (Someone please confirm this or refute it) the bokeh control changes the shape of the aperture, (rounder or straight sides), and moves it longitudinally to maintain correct aperture as well. Does that achieve much of the same benefit?

great for speculation over a drink or two. Hell it took almost that to make me think this idea up in the first place
10-20-2010, 01:00 PM   #8
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QuoteOriginally posted by yusuf Quote
This is not a soft focus lens, it's a very sharp lens with ability to control bokeh. Read the link in OP.
Yeah, we got nothing like that. I did read the link, but very disappointed there were no pics (with the lens, of course)!


Last edited by farfisa; 10-20-2010 at 01:12 PM.
10-20-2010, 01:28 PM   #9
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QuoteOriginally posted by Lowell Goudge Quote
if (Someone please confirm this or refute it) the bokeh control changes the shape of the aperture, (rounder or straight sides), and moves it longitudinally to maintain correct aperture as well. Does that achieve much of the same benefit?
The link already provided to Nikon's website describes how their lens works:

"Well then, can we implement such a lens that allows varying the defocusing characteristics by changing the aberrations a little bit? This approach would be able to realize the ideal lens accepted by all of those who demand sharpness or want to utilize the out-of-focus foreground, and for those who call for a soft out-of-focus background.
He carefully examined the data on the Gaussian lenses to find a method for changing the shape of spherical aberration alone without increasing the other aberrations. Finally, he found the solution: the challenge can be solved by changing the distances between the lens elements in the front group of Gaussian lens."

The Sony 135mm f/2.8 [T4.5] STF works differently:

"A special 'apodization element' is situated near the aperture of the lens optical system. This special optical element is a type of ND filter which gradually becomes thicker (darker) towards the perimeter, thereby reducing the amount of light that passes through around the outer perimeter. The aperture of this lens is indicated and controlled by the T No., which compensates for the reduction imposed by the special apodization element. The T No. can be used as the F No. on a normal lens when the exposure is determined."
10-20-2010, 04:47 PM   #10
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Yep, the Sony basically has a ND stuck in the middle of it, which is why light transmission drops to T/4.5 (and worse) at maximum aperture. The photos I have seen with this lens stun and amaze me. For example, this one.
10-21-2010, 02:11 AM   #11
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Here's an explanation of what influences the quality of bokeh:

Bokeh

It describes the effects of spherical aberration correction and actually mentions the Nikon DC lenses.

Presumably the "defocus control" will allow the user to choose a compromise between gross undercorrection (soft focus and great bokeh) and optimal correction (sharpest focus and good bokeh).
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