[rollsman4]

I am looking to see if the IQ can be improved over the Pentax 645 lenses. Any suggestions and if adaptor is available. I would like an 80mm lens to start. Thanks
Or 60mm in that area and portrait lens. Thank you

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Last edited by rollsman4; 11-01-2018 at 09:52 AM.

[IgorZ]

Don't know about the IQ comparison, but the lens that produces the biggest number of keepers is Carl zeiss jena Sonnar 180 f2.8. Honestly, if I nail the focus it's a keeper. Comes in a pentacon six mount which is easy to adapt to the 645.

[rollsman4]

Where do I get the adaptor for it? Thank you

[IgorZ]

Hartblei produces adapters for it. I bought mine on ebay.

[Digitalis]

I am looking to see if the IQ can be improved over the Pentax 645 lenses.

The older Contax 645 lenses perform optically about on par and only in certain specific instances and situations slightly above current pentax 645 offerings. The biggest handicap being exclusively manual focus, manual aperture only (meaning limited AE control). The older coatings used by Zeiss cannot keep up with current pentax SMC, contrast really suffers at wider apertures. The 645 Zeiss Sonnar 80mm f/2 commands extortionate prices, well above what the lens originally cost when included with the Contax 645. Tests from my Optics bench have shown that 0.8 stop speed increase in speed brings a hefty reduction in resolving power and only a marginal "improvement" in shallow DOF*.




* Vignetting and astigmatism is a problem too...probably just as well the Pentax 645Z has a 33X44mm sensor...anything bigger than that yeesh.

[Bob L]

As far as the CZJ offerings go you should stick with the later MC (multi-coated) versions. The two that stand out from the crowd are the 180/2.8 Sonnar and the 120/2.8 Sonnar with the former being quite a heavy lump but worth trying if weight isn't going to concern you.
The 50/4 Flektogon is useable (but not special) and the 65/2.8 Flektogon was dropped before the MC's came out so that eliminates it from the potential choices. I really think that the Pentax 67 55/4 (final version) is probably the best option out there if you're looking at 60mm+/- away from 645 lenses.

For the 80mm, the CZJ 80/2.8 Biometar is acceptable, compact and cheap (it was the Pentacon Six kit lens) but isn't going to get remotely close to the D-FA 645 90mm lens.

Bob

[Digitalis]

I really think that the Pentax 67 55/4 (final version) is probably the best option out there if you're looking at 60mm+/- away from 645 lenses.

Though the Pentax 645-DFA 55mm f/2.8 ASPH would comfortably outperform the 67 55mm f/4 lens @ f/4...while also providing the additional boon of full AF and AE support.

[Bob L]

Though the Pentax 645-DFA 55mm f/2.8 ASPH would comfortably outperform the 67 55mm f/4 lens @ f/4...while also providing the additional boon of full AF and AE support.

It does indeed and I only raised the 67 55/4 as the op seemed to be looking outisde the 645 stable.

[Ed Hurst]

Funnily enough, I think it depends. I have found that the 645-DFA 55mm performs very well up to middle distances, but when it comes to resolving details in a distant scene, the latest version 67 55mm seems to me to pull level or even have a slight advantage.

[Digitalis]

I have found that the 645-DFA 55mm performs very well up to middle distances, but when it comes to resolving details in a distant scene, the latest version 67 55mm seems to me to pull level or even have a slight advantage.

The Pentax D-FA 55mm f/2.8 ASPH lens has a flatter focus field at closer distances than the 67 55mm f/4 lens, but that field curves a bit as focus shifts towards infinity which introduces slight astigmatism.

[rollsman4]

Thank you for all your responses and suggestions. I decided to stay with the Pentax 645/67 Lenses

[rollsman4]

Thank you for all your responses and suggestions. I decided to stay with the Pentax 645/67 Lenses

[rdenney]

Thank you for all your responses and suggestions. I decided to stay with the Pentax 645/67 Lenses

That’s a good choice.

The 180mm Zeiss Jena Sonnar is a lens for portraits. The bokeh is creamy—perhaps the best of any medium format short telephoto lens ever made for faded edge bokeh. But what makes that work is slightly under-corrected spherical aberration. It is just not as pin-sharp as a modern lens, nor with the same contrast at high spatial frequencies. All that is ideal for portraits, perhaps less so for landscapes.

(The CZJ 120 is not a Sonnar, but a Biometar, similar to a 5-element Planar.)

The Pentax lenses will have more contrast at low spatial frequencies, a reflection of Pentax’s design sensibilities. Pentax lenses never played second fiddle to German lenses for similar applications (SLRs), despite the romance.

Rick “who prefers the 67 45mm lens to the 67 55/4” Denney

[Digitalis]

The 180mm Zeiss Jena Sonnar is a lens for portraits. The bokeh is creamy—perhaps the best of any medium format short telephoto lens ever made for faded edge bokeh.

I work with the Leica APO-Elmar 180mm f/3.5 CS lens which like the CZJ 180mm, is absolutely superb for portraiture on the Leica S. I'm just saying it - Leica could make a killing if they decided to make those lenses for other camera mounts.

he Pentax lenses will have more contrast at low spatial frequencies, a reflection of Pentax’s design sensibilities.

I think this has more to do with the quality and number of optical coatings than any inherent optical design philosophy. The later PS series lenses from Bronica held a distinct advantage* in image contrast compared to the older S line, merely by improving the coatings.

The CZJ 120 is not a Sonnar, but a Biometar, similar to a 5-element Planar.

Biometar/Biotar** is east German parlance for Planar. "..A rose by any other name..."

The name Biometar/Biotar/Planar pre-date WW2. Naming conventions were adhered to more strictly than they are now.



* what made this more obvious is a lot of the optical formulas used in the S and PS line were identical.
** Biotar is an Assymetrical Planar, a Biometar is a tweak of the planar formula, which is comprised of 5 elements. Where the Biometar diverges from the Planar design only by substituting the rear doublet by high curvature singlet elements.

[rollsman4]

Thank you all for sharing this info.