How good is the Zeiss 35-70mm f3.4? Can a zoom really match a prime?

Zeiss Contax 35m f2.8 Distagon v Zeiss Contax 35-70mm f3.4 v Sigma 24-70mm f2.8 EX DG
Zeiss Contax 35-70mm f3.4 v Sigma 24-70mm f2.8 EX DG v Canon 50mm f2.5 Macro

The real point of this test is to determine the substance of the claim made
by many that the Zeiss 35-70mm zoom equals the performance of the primes in
its range. As it happens I have a 35mm f2.8 Distagon prime which I rely on
quite heavily for architectural work where it is an f8/11 workhorse. I've
previously stated that if there is a sharper lens at this focal length,
I don't need it.

I also picked up a late model Sigma 24-70 DG recently which I wanted to put
through its paces, which makes an interesting counterpoint to the Zeiss:
the Contax lens is push/pull, silky and silent MF, 85mm long, 67mm filter,
f3.4 and appealingly lightweight, despite being hewn from metal; the Sigma
on the other hand is a 'conventional' two-touch zoom, half a stop faster,
and looks - and sounds - like it was requisitioned from Robocop's ambulatory
system - it is huge, and quite deeply unattractive: a tapering 125mm lunk
with an 82mm front filter ring. This ugly duckling has lost the limelight
to Tamron's svelte little 28-75, but its used values have therefore
obligingly been depressed. User reports indicate that the late DG Macro
designated lenses are optically superior to the earlier models - a rumour
unsubstantiated by Sigma. So much for the cover; what's the book like?

 

35mm f4 Test: CLICK IMAGES FOR LARGER 100% CROP

Sigma 24-70mm at 35mm / f4 (Edge)	Contax 35-70mm at 35mm / f4 (Edge)	Contax 35mm at 35mm / f4 (Edge)

 

What we have here is thoroughly commendable performance from the Sigma,
one stop down - still not sharp, but OK - great performance from the Contax
zoom barely half a stop from full aperture. The Zeiss 35mm prime is shown here
wide open - at a comparative f4 it is superbly sharp - see here for proof!

 

35mm f11 Test: CLICK IMAGES FOR LARGER 100% CROP

Sigma 24-70mm at 35mm / f11 (Edge)	Contax 35-70mm at 35mm / f11 (Edge)	Contax 35mm at 35mm / f11(Edge)

 

Everything's hunky dory at f11, but still the Contax zoom is hunkier than the prime.
Straight from the camera, the difference is even more pronounced in favour of the zoom,
but I've corrected the zoom for barrel distortion, robbing the original capture of a
little of its bite - the prime is almost perfectly corrected for geometry.
Still the zoom is better!

 

50mm f4 Test: CLICK IMAGES FOR LARGER 100% CROP

Sigma 24-70mm at 50mm / 4	Contax 35-70mm at 50mm / f4	Canon 50mm Macro at f4

My benchmark 50mm is the Canon Macro: if the 35-70mm comes close, it's a special lens.
Lo and behold, at f4, they're all excellent - even the Sigma. Once again, though,
if there is a winner by the barest whisker for contrast and resolution, it is the
Zeiss zoom.

 

50mm f11 Test: CLICK IMAGES FOR LARGER 100% CROP

Sigma 24-70mm at 50mm / 4	Contax 35-70mm at 50mm / f4	Canon 50mm Macro at f4

And finally, at f11, the zoom still manages to leave behind not only the Sigma zoom
but also the Canon prime. What a performer.

 

Conclusion:

I'm sold. The Contax 35-70mm is a very special lens. It's macro capability, while not
equalling the 1:2 or better of dedicated lenses, greatly extends its usefulness for
field work. Superb across the frame performance is delivered to the 16.7MP 1Ds II sensor,
making it well worth the cost of an adaptor and the penalty of stop down metering in
applications where rapid response is not critical. Moderate barrel distortion will
require correction (typically -3% spherize) for geometry-sensitive subjects.

Corroboration of the resolving power of this lens can be found here - where at 35mm
it it shown to outperform the Canon 35mm f1.4 and Contax 35mm f2.8.

Not to forget also the Sigma 24-70mm, which made a good showing against stiff
competition. Very modest 'Sigma yellow; here, and very respectable across-the-frame
performance at a bargain price. At 35mm, the Sigma shows fairly pronounced
pincushion distortion.

Tests were conducted on a 1Ds II with shutter lockup at ISO50. USM of 150 / 0.5 / 3 was applied to each C1 developed RAW file before dot-for-dot screen captures were taken in Photoshop, PDF converted and saved for web with Pro JPEG. Focus bracketing was deployed to ensure accurate flat-field test results. Special thanks to the long-suffering brick wall.