[Fenwoodian]

.
Well, that settles it then....

I just bought a used 67 105/2.4 lens. I don't have a 645D yet, but I do have a 67 to K adapter and I'll try out the new lens on my K-1. I'll be sure to let you all know what I think of it on the K-1.

[texandrews]

I'll jump in. My experience has me favoring the FA150 2.8 and 67 105/2.5 for smooth bokeh.

Mike SF would know!

[Fenwoodian]

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I received my used 67 105/2.4 lens in the mail today. Below are a few quick test photos (all at f/2.4) I took with it on an adapter on my Pentax K-1 camera.

My overall impression - MEH. Some C.A. Low contrast. To my eye, just average sharpness, 3-D pop and bokeh.

Maybe this lens performs better on medium format bodies; but for my K-1, I'm going to stick with my Zeiss and Leica full frame lenses.
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[rdenney]

I cannot disagree on the 105. I think its reputation stems from its speed at that focal length, which allows selective focus with a lot of blur in the background. But it’s a long normal for the 67, and a double-gauss designed for sharpness like most Japanese normal lenses.

I would love a lens with a vintage Sonnar design in that focal length for the 645. I fear it would not fit in front of the mirror, but it might. Sonnars were originally intended as fast normals for rangefinders (example: the original early-1930’s Sonnar was a 50/1.5 for the Contax—that was even before the Olympia Sonnar 180 of 1936).

But there aren’t a lot of choices for 645 in the 100-120mm focal range intended as short portrait lenses. A 110/2 with a vintage Sonnar design would be spectacular.

Rick “lenses designed for extreme sharpness wide open—successfully by modern standards or not—may compromise bokeh to get it” Denney

[Sandy Hancock]

I have the FA645 75/2.8, FA645 120/4.0 macro, FA645 150/2.8 and FA*645 300/4.0. All produce very nice out of focus rendering.

But when all is said and done, my Schneider-Kreuznach Cinelux-Ultra 125/2.0 is the bokeh king.









I would certainly like a 67 105/2.4 though....

[Sandy Hancock]

Mind you, there's not much wrong with the FA645 80-160/4.5 zoom either....

[Sandy Hancock]

FA645 75/2.8 wide open



And stopped down a bit

[Sandy Hancock]

Unfortunately, my DFA645 90/2.8 macro has been out for repair since I realised it did not focus beyond about 5 metres, so I can offer no examples.

[Thorrulz]

Pentax 645D with Pentax 645 FA 200 f4 @ f4


Nikon D800 with Nikon 200 f2 @ f4


Pentax 645D with PENTAX-FA645 45-85mm F4.5 @ 85mm and f5

[texandrews]

Pentax 645D with Pentax 645 FA 200 f4 @ f4


Nikon D800 with Nikon 200 f2 @ f4


Pentax 645D with PENTAX-FA645 45-85mm F4.5 @ 85mm and f5

Looks to me like the dof is shallower in shot # 1 than # 2, which may be giving the illusion that the Nikon is crisper. The Nikon lens' bokeh seems better, but it's hard to say since the backgrounds are different (for whatever reason). Nice comparison.

Nothing wrong with the resolution of the 45-85 in image # 3 !, although the bokeh's not great imo (but that background is a bit of a torture test...)

[Alex645]

Pentax 645D with Pentax 645 FA 200 f4 @ f4

Nikon D800 with Nikon 200 f2 @ f4

This helps to illustrate how DOF (and bokeh) are affected by format size. A 105mm on a 645 will have less DOF and more bokeh than the same lens on a full frame K1.

[rdenney]

This helps to illustrate how DOF (and bokeh) are affected by format size. A 105mm on a 645 will have less DOF and more bokeh than the same lens on a full frame K1.

Only because the camera had to be backed up for the Nikon shot to get the same subject size, resulting in a smaller piece of the background being enlarged to the size of the frame. If the camera and subject position stayed the same, and the larger format was cropped to show the same scene and then enlarged to the same print size, the depth of field would be identical.

But it’s not “more” bokeh. Bokeh is a quality assessment. More blur often seems like better bokeh, but correct comparisons need the same blur size to make judgments of bokeh.

Rick “who made some photos with the 150 today, but hasn’t studied them yet” Denney

[Alex645]

Only because the camera had to be backed up for the Nikon shot to get the same subject size, resulting in a smaller piece of the background being enlarged to the size of the frame. If the camera and subject position stayed the same, and the larger format was cropped to show the same scene and then enlarged to the same print size, the depth of field would be identical.

But it’s not “more” bokeh. Bokeh is a quality assessment. More blur often seems like better bokeh, but correct comparisons need the same blur size to make judgments of bokeh.

Further into the linked article is a good explanation of the relationship between DOF and format size:
Depth of Field, Part III: The Myths | B&H Explora

...and yes, bokeh ≠ dof, but the less dof, the more apparent the bokeh, regardless if the bokeh has good, bad, or ugly qualities.

[672]

its the P67 75mm f2.8 AL wide open.

[TDvN57]

I'll jump in. My experience has me favoring the FA150 2.8 and 67 105/2.5 for smooth bokeh.

I agree on these two lenses as bokeh kings.