In praise of the Pentax 645 FA 35mm f3.5


Elegy or Eulogy?

Given the present uncertainty as to whether Hoya/Pentax have axed the long awaited Pentax 645 Digital, the undervalued Pentax 645 range of medium format optics remains practically homeless.* While Mamiya 645 users are exploring the realms of possibility opened up by the ZD back and body, rediscovering the excellent lenses in the Mamiya line, an even better range of optics has tragically been orphaned.

If we're talking about the sharpest medium format optic, we naturally think of the Hasseblad 120mm Makro. Mamiya users have already discovered that their new AF 120 Macro is very close to its equal. What remains under-publicised is that the Pentax version is at least as good. Until the very recent release of the Mamiya 28mm which, at the time of writing, is suffering a number of teething / compatibility problems, Pentax' mould-breaking 33-55mm zoom was the widest rectilinear lens available for medium format: a sorely needed commodity with the present generation of undersized MF sensors. However, the true star of the range is the autofocus FA version of the Pentax 645 35mm f3.5. This is truly the Zeiss 21mm f2.8 of the medium format world, towering above its peers. Using medium format lenses on 35mm can be a bit of a lottery but the Pentax FA35 is a safe bet.

Consider the following data extracted from PopPhoto's tests, back in the day when they used to do the job properly, publishing lpmm figures for centres and corners. Here's the quoted data for the state of the art, brand new Hasselblad IF FLE 40mm f4, set alongside the current AF Mamiya 35mm f3.5 and the Pentax equivalent. The strongest performer at each aperture is emboldened:

Hasselblad 40mm IF FLE
Mamiya AF 35mm f3.5
Pentax FA 35mm f3.5
Centre (lpmm)
Corner (lpmm)
Centre (lpmm)
Corner (lpmm)
Centre (lpmm)
Corner (lpmm)
f4
74
47
70
35
68
34
f5.6
74
47
74
39
76
38
f8
74
52
62
35
76
54
f11
59
42
62
39
76
54
f16
59
42
60
39
68
43
f22
52
37
49
35
48
38
f32
43
34

Ask an impartial observer to nominate the best MF wide angle and chances are they would say Hasselblad – especially an all-new design – but overall the wider Pentax 645 lens easily outresolves the 'Blad. Crucially it's really on form at typical working apertures. True, the IF 40mm is outstanding wide open, especially in the corners, but the Pentax glass owns f8 / f11. The gulf here between it and the highly regarded Mamiya – and the Hasselblad! – is telling.

At f8, the Mamiya is way off the pace but by f11, there is little choose between the Blad and the Mamiya at f11 and f16. But at f11, the Pentax is out on its own. And when you consider the price of the Hasselblad lens, the Pentax FA35's performance becomes even more impressive.

But will the difference be visible on the big, lazy Dalsa chip in the ZD? After all, there are many happy Mamiya 35mm f3.5 users . . . ? But then again there are no Pentax 645 / ZD users out there yet – happy or otherwise. Do the maths: the Mamiya's 39lpmm corner resolution is not enough to resolve adequately on a 56.1mm wide 22MP chip, whereas 54mm is pretty close. I think the difference would be clearly evident.

Given that the pixel pitch of the Mamiya ZD back is almost identical to that of the 5D, we can use a Zörk shift adaptor to gain a fair idea of how this lens would perform if adapted to the 22 megapixel Mamiya 645 AFD/ZD combo. From my experience with the lens on 5D and 1Ds II bodies, I am far more interested at this point in adapting the lens for use on the ZD than downtrading to the Mamiya equivalent.

**Update:**
Having spent considerable time looking at the adaptation of the Pentax FA35 for the Mamiya mount, I can see that it is feasible, but may require a minor mirror mod to the Mamiya body. It also entails the removal of the FA35's rear mount and it's not easy to disentangle the aperture and AF mechanism from the bits you need to discard. Wearing a donor Mamiya mount, the rear element needs to protrude beyond the flange to provide correct infinity focus. Somewhere along this conversion, I decided for other reasons to abandon the Mamiya body altogether and use selected lenses from the range on the excellent 1Ds III. I can't therefore report from the front, as it were, but I got close enough to see that it's a viable concept that I would have seen to completion had I stuck with the body.

* One year after this was written, we can amplify with greater authority the statement that the system is dead and buried. RIP Pentax MF.

 

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