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Saturday, October 27, 2012

••◊ Buying a (good) Zeiss 50mm lens

While I'm knee deep in post production, I thought I would write this post about one of my more recent screw ups.  As usual, this started with the best of intentions.  I wanted to buy a set of "good" prime lenses that I can use in the long term for video work.  From what I've seen so far, the Zeiss ZF.2's are the only game in town in the quality versus price trade off.  The CP.2's are the same lenses with cinema mechanics applied and a huge price bump.  The Samyang, Rokinon... or whatever they brand those lenses as this week just weren't going to cut it as far as glass quality.  I've learned my lesson too many times about buying cheap stuff!

So I thought I was buying a good lens by starting off with the nifty-fifty Zeiss 50mm f/1.4 lens.  I had it in my hands, paid - it was mine.  The lens is supposedly German quality, right?  Then I started doing my research. 

I found a number of reviews including those from Ken Rockwell.  He did a comparison of a half dozen 50mm-ish lenses from different eras and the Zeiss was clearly a lemon among the group.  Then again, this is the cheapest still lens Zeiss (sort of) makes.  Their low end lenses are made by Cosina in Japan.  You have to have big-boy money to buy real German glass.

I also found a useful website from the folks at DxO Labs, called DxOmark.  They have compiled data from hundreds of lenses and have it available for free!  Let's start with the overview data they offer.

What I immediately see is that there is a clear difference in resolution (sharpness) between the two lenses (pun intended).  The f/2.0 macro also offers much better chromatic aberration performance (red and blue fringing at image edges) than the f/1.4.  To understand what I'm buying I dove into their individual performance charts.

The f/1.4 lens doesn't appear to be sharp until it's stopped down from f/4 to f/8, whereas the f/2.0 macro is sharp from almost f/2 to f/8.  Not exactly as sharp as the f/1.4 right at f/5.6, but probably close.  Plus, the macro lens is useful over a wider range of usable apertures.

I intend to use this lens right about f/4, so I think we can call the vignetting a tie.  The lenses are both excellent in this regard for my usage.  At f/2.8 the macro lens falls off by a stop.  I can deal with that, especially on a super-35mm size sensor.  This data assumes a full frame, so the performance is actually much better than this chart would indicate.

The chromatic aberration performance was the absolute tie-breaker for me.  I want to use this lens for video work, so it can't have aberration problems.  Unlike still photos, there is no CR2 file to correct in post here.  Chromatic aberration is a sure fire way to permanently screw up a video image and perceived sharpness.  Notice how the f/1.4 is pretty bad throughout the aperture range and the macro lens is absolutely excellent?  This caused me to return the f/1.4 for the f/2.0 macro.  Yes, I know it's nearly double the price, but I'm buying a set of lenses for the long term.  I want the best I can afford.

I highly recommend checking out DxO Labs web site before buying a lens.  This is a true gem of information on the Internet.

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