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 p.2 #15 · CONTAX C/Y CARL ZEISS VARIO-SONNAR T* 28-70mm F3.5-4.5 MM | |
Slow zooms are an alternative way of seeing, for a different look - the full detail look as humans actually see the world. A short take on this great 28-85 compared with a few primes, based on MTF:
The 28mm short end is a wide angle bonus on a very sound zoom. The 35-70 is a low distortion corner to corner star, which has similar central performance from f3.4 to f8, and stopping down picks the wide edges up to almost equal levels.
The 28-85 is a lens which delivers a very large increase in performance at all parts of the frame upon stopping down to f8, for fine to moderate detail rendition - the 'large object' contrast already being at very high levels wide open - this shows as a very bright image with very accurate outlines of main subject material.
briantho, you may agree that many subjects are well presented with excellent middle aperture quality to combine with excellent depth of field.
I looked up the Zeiss data for perhaps the best mid and long ZE lenses, the 50MP and 100MP, 'best' here meaning peak raw performance in contrast terms, characterised by MTF.
At 50mm in the image centre at best aperture, the 28-85 shows for 40-20-10 lpmm figures of 76-88-95 and the 50MP shows 76-88-94. Over most of the frame, lines are very high for both with a small decline, a little more in the zoom. Distortion is near identical in both - around 0.7% at 20mm image height (corners).
At 85mm at best aperture the 28-85 at 85mm delivers 40-20-10 centre data of 70-86-93 and the 100MP gives you 70-85-93. Distortion is nearly zero for the great 100MP but only 1.6% for the zoom, which is extremely good.
It's true the zoom is less consistent at 28mm but even there its centre at f8 is 76-89-95, and the ZE 28/2 gives us 73-89-96 at f4.
Central performance is very important because that is where the viewer most often forms the impression of sharpness and level of detail, and it's also where most important subject matter is shown in most images. We can lose sight of that sometimes in the quest and concern for great corner performance.
Measurements above are from the highly accurate, industry standard Zeiss K8 precision instrument as seen at the link below, along with an interesting read:
http://www.zeiss.de/C1257569004B5D2C/EmbedTitelIntern/MTF-TesterK8/$File/Carl_Zeiss_MTF_Tester_K8.pdf
Almost all lenses perform best two stops down, and these data for the primes presented above are for f4 (28/2 and 100MP) and f5.6 (50MP). They are much worse at f2, all three of them, often disguised by close focusing on a nearbly subject.
They will also drop off in performance at the aperture very often needed for many photographers - f8, for a balance of residual aberration control against diffraction onset, on the camera format for which they were intended, 35mm - now better known as 'full frame'. So the above comparisons move in favour of the zoom at f8, two stops (or thereabouts given the variable aperture) down for it.
Even a 28mm prime gives poor depth of field at f4 (two stops down), and as for 50mm and 100mm, you had better enjoy out of focus performance because that is your lot at f4, for all but shallow depth or planar images.
Not many people enjoy detailed landscape images shot at f4 for such focal lengths, for example, this is one reason many landscape photographers prize TS/PC lenses highly. You could say that fast primes peak too early, but of course they have other uses and applications.
The Contax zoom lenses are extremely landscape and 'deep image' friendly, as are many Contax primes; the mid to long lenses in the ZE/F range are much less so, seeing as they are optimised for what might be called more 'modern' uses and styles. This is clear from a quick trip to the ZE/ZF/ZM image thread. Choose any page.
The manufacturers are working flat out to provide a broader range of low to mid ISO performance and they are getting there quite fast, so we will soon see ISO 50-400 (for example) giving similar results - and that 3 stops of course moves the debate in favour of slow lenses...for peak IQ.
I write this because there may be a tendency for newcomers to the alt world to believe the 'primes are faster/better/best, zooms are slow/worse/bad' meme, but it's not necessarily so. You might need to buy a 10-15 year old zoom lens to see it. Many deliver great results from wide open, but not this 28-85 one.
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