PHOTOOG Photography writings by Olivier Giroux

16Apr/103

The un-ideal lenses

Just today DpReview posted data for the m4/3 ultra-wide zoom from Olympus, the M.Zuiko 9-18mm f/4-5.6 ED. I have mixed feelings about the results and what they mean for serious photographers who would adopt the lens. I thought I might share this with you.

Ideal lenses

I’ve long been an enthusiast of what I will call ideal lenses. I call them ideal because they behave in an idealized manner, as if following a mathematical rule of thumb. The most widely used ideal lenses are the old spherical classics.

Wide open the ideal lens is not a terrific performer, with lower than optimal contrast and micro-contrast, but with generous dosage of softly-rendered defocused regions. As you step down the ideal lens its contrast and micro-contrast eventually renders beautiful detail in all its glory, as good or better as the latest imaging devices can record. While the quality of the image detail improves, the quality of the Bokeh becomes more neutral.

The relationship of the ideal lens to its aperture setting is one of direct proportional improvement of technical qualities towards smaller apertures. Up to a point of course. That point being the diffraction limit for combination of the lens and the imaging device – most commonly f/11 for current devices.

The old classic designs named Gauss, Biogon, Sonnar and Tessar are all ideal lenses in their native spherical implementations. Their characters change appreciably as you turn the aperture ring through every click. The photographer effectively gets multiple lenses in one of these, much like a zoom, with multiple choices of rendering style to apply to taste.

Lastly, the peak quality that a Gauss or Biogon design can deliver at f/8 is simply astonishing. This is one of the most solid virtues of the ideal lens: no matter the exotic new lenses that become available 30 years from now, a current-day Biogon will still stand among the best of them when it is stopped down. The ideal lenses can serve for a lifetime.

Un-ideal lenses

Enter into our tale the new-generation Japanese lenses in general, and the M.Zuiko 9-18mm in particular.

These are computer-generated designs with up to 3 or 4 molded aspheric elements that reduce the design by as many as 10 or 12 elements as a similar spherical design would employ. In my opinion this sounds like a cost-saving measure because with such small maximal apertures the spherical aberrations are not likely that difficult to control.

We can plainly observe from the test results that the 9-18mm zoom is not an ideal lens. It is at its best when wide-open and in this case it is not hyperbolic flattery. You start with what I’ll call average performance at the beginning of the aperture series, and then there is no more quality to be got from it no matter what you do with it. If the ideal primes are like zooms in character, this un-ideal zoom is like a prime in character.

My hypothesis is that the reduction in the number of surfaces made possible by the multiple aspheres (note: a pull away from the Zeiss design-relaxation philosophy) has the side-effect that the complete extents of all surfaces is needed for the lens to be properly corrected. As you step down the 9-18mm you may be robbing from it the surfaces it needs to produce corrected images. This is my poorly-educated hypothesis that attempts to explain the data.

How to judge the value of the un-ideal lens then? I see it as very limited to be honest with you. The 9-18mm fills a need that few other lenses do – exactly one other lens actually, which has similar issues but to a lesser extent.  But in the long term both of them are likely to be forgotten, replaced by enhanced versions of themselves ad infinitum.

The truth is that the small sensors (by film standards) in the m4/3 cameras mean that ideal designs are not pre-existent on the market, you cannot borrow a 9mm ideal lens from a different system because none exist. It will be up to Olympus or Panasonic to come up with these designs, or their market to become important enough for Zeiss to step into that niche. That could not be a Biogon design, but it could be a Distagon.

Either scenarios seem extremely unlikely to me however. People who care about ideal lenses also care about larger sensors. For no better reason than that, and it is a poor reason, ideal lenses are tied to the old 24x36mm format.


Comments (3) Trackbacks (2)
  1. I also read that review of the Olympus 9-18mm with interest. Like you, I use a D700 to take photos, primarily of my kids. Inside the house, that works beautifully. I mostly use the 24-70mm f2.8 lens. While not up Zeiss standards, it is a good lens. I find my kids move too fast for my manual focus skills.

    I’m having a struggle on what do use when I leave the house. Especially when we go out for the day on weekends, I’m not wanting to lug the weight of the D700 around.

    I suspect from reading your blog you’ve been going through the same thoughts as I am. The M9 would be great, except it is silly expensive. What to do when we want lighter weight? You seem to be thinking D700/24mm 1.4. But to me even that is over the weight threshold.

    I went out this weekend and got a Panasonic GH1 with the kit zoom and 20mm f1.7. It it too early to say, but I got a few good shots with the 20mm on my first day.

    For a “day out” kit, the 9-18mm would be an ideal size. I agree that the 9-18 review left me a little flat on image quality. However, I might get it anyway, and see how many shots I get that would be have been missed because I didn’t have my camera with me.

    Are you tempted to get a MFT, despite the limited lens choices you mention?

    • Thanks for the comment Craig.

      Yes I feel your pain. The D700 is never a compact camera even when it’s wearing nothing but a body cap. When I want to go out light I put on the 1.4/50mm Planar ZF – it makes the combination about as long as it is wide, about as compact as it gets.

      I’m not seeing the 24mm f/1.4 as a lightweight day-hike lens, I’m interested in it for other reasons. Reportage photojournalism is a genre that I am intellectually invested in and this lens is the best tool for that specific job. I will be renting it later this month and writing my own (dry, 100% text, but hopefully enlightening) review.

      About that Panasonic 20mm lens – test data shows it has some ideal characteristics. Interestingly it weakens around f/5.6 and is back near its wide-open performance soon after f/8. I wonder if that is not simply the diffraction limit on these 4/3 cameras and the 9-18mm just happens to hit the limit right out of the gate because it is such a small maximum aperture lens. Obviously the next step below f/5.6 is f/8…

      Do the m4/3 cameras appeal to me? Yes, but they don’t make proper use of the really good lenses in this world (even if they can mount them). The 2x crop factor really hurts.

      It’s all about the lenses for me. If that wasn’t obvious. ;^)

      Olivier

    • Hello Craig,

      Reading your story I must tell you I have the same second thoughts of lugging around my D300 everywhere.

      The options I found (and that might help you) are:
      –D300 plus CZ 25/2.8 or CZ 50/2.0
      This makes a wonderful and rewarding combination! But still on the heavy side of things. Image quality, however, is as good as it gets on Nikon F.

      –Konica Hexar RF plus CV 35/1.4 or Hexanon 50/2.0 with FP4 or HP5 film.
      This is smaller and more lightweight then the D300 kit in the former point but it also is wonderful in its use. Very easy to use, intuitive and wonderful in its rendition of reality. I scan the negatives to get it digital….

      –Olympus OM2n plus 35/2.8 or 50/1.4 or 85/2.0 with FP4 or HP5 film.
      This is a wonderful set too. Very intuitive to use, lightweight and compact. Lens quality lacks behind the other options but the lenses I name above have a beautiful drawing in B&W albeit not with the best sharpness and contrast.

      Maybe you, and other readers, can benefit from this post.

      All the best!

      Greetings,

      Marc-paul


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