Tuesday, September 22, 2009

Comparing Medium Format Lenses

photographyPhotography geeks love lens tests. They provide a quantifiable measure of one lenses worth versus that of another. They can be used to justify purchases, even if the desired lens has only a fractional improvement over one already owned. Some say that it's not the equipment, it's the photographer that makes a great image. Others say that you can't take good photos without good tools. Of course there is a measure of truth in both viewpoints.

In this article I'll examine how important lens quality is, in light of medium format. And then I'll look at some particular cases. The results may surprise you.

Due to the nature of their sensors, digital cameras are very particular when it comes to optics. And the smaller the sensor the harder it is to design excellent lenses for that camera system. Thus it is harder to design a lens for an APS-C digital camera than it is for 35mm film, and much harder than it is for medium format. In fact, pretty well any medium format lens is good enough for taking decent photos! I don't know about you, but before I began researching medium format, I was completely unaware of this fact.

How do we go about testing lenses? Well, that is a complicated issue, which I will leave to Norman Koren's Lens Testing article to describe. You may also wish to peruse the insane details in Understanding MTF and Do Sensors "Outresolve" Lenses? Or, you may wish to simply understand that sharpness can be gauged by seeing how easy it is to distinguish small details in a photo. That's a massive simplification but will do for now.

Of course sharpness isn't the only measure of a good lens. Does it provide a distortion-free image? Is it resistant to flare? Does it produce accurate colours? How does it handle? How large or heavy is it? Does the filter size conform to established standards, or even what you already have in your kit? And how about chromatic aberration? What is the bokeh (quality of the out of focus regions) like?

But despite all this, photographers come back to sharpness as the most important determinant of lens quality. Maybe because it's easy to test. So let's forge on ahead and pretend for the moment that sharpness rules the world. Let's have a look at some 645 camera lenses and see what our money buys us.

David Garth in the newsgroup rec.photo.equipment.medium-format aggregated lens tests from Popular Photography. The Zeiss Planar 80mm f2.8 (priced at $1600 at the time), 90mm Schneider Makro APO-Symar ($3200) and SMC Pentax FA-645 75mm ($420) were compared. The result? The Pentax was on par with the Schneider and bested the Planar almost across the board, being much better at some apertures (70 versus 44 lpm at f/11, for example; higher lpm being better).

Or maybe we should compare the SMC Pentax-A 645 35mm F3.5 to the Hasselblad 40mm IF FLE and Mamiya AF 35mm f3.5, as PopPhoto did back in the day (see 16-9.net). Again the Pentax lens is superior (except wide open), beating the Hassy 76 to 59 lpm at f/11. And it's the only lens in the test to stop down to f/32.

Pentax offers the best value lenses in the 645 format. They are not only "good for the price" they are "good at any price". Spending more does not get you better lenses. Not even if you spend ten times as much!

(It's at this point that some critics are wont to call me a Pentax fanboy. But don't fanboys love their brand despite evidence to the contrary? I can only find evidence that Pentax rocks for someone on a budget.)

But nonetheless I must issue a couple of provisos before you go charging ahead into Pentax land.

First, be sure that Pentax 645 has the lenses you need. Though there are primes from 35mm to 400mm, a few handy zooms and a 120mm macro, the Pentax system provides only two leaf shutter lenses, a 75/2.8 and a 135/4. Other systems might have more lenses or some specific features you need for your work.

For example, Pentax 645 lenses can be fitted to K-mount cameras with a simple adapter. So can Pentax 6x7 lenses for that matter. This allows you to save on lens purchases and how much you carry at once. Maybe some other system has its specific benefits?

Second, before buying a system check to see what the real-world availability is like at the present time. It may sound obvious, but just because a company made a dozen lenses forty years ago does not mean they are readily available now. And also some camera systems have exorbitant prices due to their collectability (that is, nothing to do with their use as a tool). This is annoying to photographers but an unfortunate fact of life.

It turns out that Pentax lenses are still available, and at very reasonable prices if you shop around. But they are maybe not all as plentiful as one would like. And they are no longer being supported by the company. (That's true of many medium format lines.)

In conclusion, let me repeat that pretty well any lens system is "good enough". Blind tests (an odd term to use in photography!) continue to show that photos cannot be distinguished by brand. The lovely tonality and detail of medium format seems to have a levelling effect.

In this domain it appears to be true that it's not the gear but the skill and vision of the photographer that is paramount.

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