While there is a quite wide choice of lenses available in the Four Thirds mount for the Olympus E-System cameras, some of them are premium glass — top quality but ridiculously expensive. How does $6000 for a 300 mm F/2.8 sound? While I've met some people who actually bought that lens, I'm sure I won't be able to afford it in the predictable future.

The longest Four Thirds lenses available, at least until late 2006, for us mere mortals, were two zooms: the Olympus 50-200 mm F/2.8-3.5 ZD ($800 or so, which I consider quite moderate for these specs and quality) and Sigma 55-200 mm F/4.0-5.6 DC (around $150, a bargain at the price but not a match even for the 40-150 mm F/2.8-3.5 Olympus zoom). Both offer the longest equivalent focal length (EFL) of 400 mm, i.e., a field of view similar to that obtainable on a full 34×36 mm film frame with a 400 mm lens.

Now, that is plenty. How many of us have used lenses above 400 mm with their film cameras? Still, for some applications longer lengths may be (or, at least, seem) desirable, wildlife and sports photography being two obvious examples.

Enter the Bigma (not to be confused with my Big Mama rig for the E-10/E-20 from 2001). Among the enthusiasts, this is the affectionate name assigned to the Sigma 50-500 mm F/4.0-6.3 DG lens.

The Old Bigma and the New Bigma

For the record, this lens has two versions, and their full, official names as specified by Sigma are:

1. 50-500 mm F:4.0-6.3 EX APO RF HSM, originally developed for film (24×36 mm) cameras; I will be referring to it as "non-DG" or Old Bigma. Internally, Sigma refers to this lens as Product 735.
2. 50-500 mm F:4.0-6.3 EX DG HSM, advertised as "optimized for digital cameras". We will refer to it as "DG" or just the New Bigma. This is Product 736 as per Sigma notation.

Listing all lens features, even abbreviated, as a part of the lens name is an old and ugly habit by Sigma. Let me at least explain what these acronyms mean:

• EX stands for premium external finish, i.e., means nothing at all.
• APO means "apochromatic", which is supposed to provide better correction of chromatic aberration. (In older days it meant that the focus-vs-wavelength curve was crossing zero twice, but I doubt if present-day marketing departments stick to this definition.)
• RF denotes rear focusing, where focus is achieved by moving the rear components of the lens assembly only. This has two advantages: non-rotating front, and less work for the focusing micromotor.
• HSM is used to denote a hypersonic focusing motor. Last time I looked, the term hypersonic meant greatly exceeding the speed of sound and I doubt it is in any way related to the focusing mechanism; it just sounds high-tech and helps selling things. On the plus side, lenses designated as HSM are less noisy when focusing.
• DG means compatibility with both digital (APS-C, Four Thirds) and film-sized frames; in other words, frame coverage up to 24×36 mm. I strongly suspect it means just that the lens was originally designed for a 24×36 mm frame, but Sigma judges its performance good enough for smaller image sizes.

The last one should not be confused with DC, which is used by Sigma for lenses with coverage only up to the APS-C size (being able, in principle at least, to take an advantage of this limitation: smaller size and weight, possibly higher resolution).

Additionally, the acronym "USM" is absent in the Sony/Minolta and Pentax versions of this lens: these come without the USM AF motor.

Even the manufacturer seems to be lost in these naming conventions: the New Bigma is referred to as EX DG HSM in the product page, as EX DG APO RF HSM in the lens table, and as APO DG HSM on the lens barrel itself.

The Old Bigma has been around since 2001 or so, and has proven itself as an excellent (for the price) and amazingly inexpensive (for the specs) optics. The digital samples from this lens I have seen (like these, for example) clearly indicate that people complaining about its optical quality are simply not qualified to use it.

The new model has been announced in May of 2005 (see the press release), and the availability of the Four Thirds version — only in February of 2006. That version became available in the United States only in September of this year.

Now, an obvious question may arise: did Sigma simply repackage its "legacy" film lens as "digital", or is it really a new design? A Reader from Germany, who was able to compare both version in the Nikon mount, claims that both are identical externally, the only difference being a different-colored coating on one of surfaces (in addition to the new "DG" logo, that is). All specifications also seem to be identical: size, weight, number of groups and elements. Sigma will not say what, if anything, else was changed in the transition to the DG version.

If this sounds bitchy, that's because I dislike it when a manufacturer offends my (or anyone else's) intelligence. If the old version was good enough to meet resolution requirements of the smaller, digital frame, and if the rear pupil geometry was suitable for the directional characteristics of digital sensors (neither of these conditions can be taken for granted, but they seem to be met in this particular case), then there would be nothing wrong with stating simply "our lens turned out to be good enough for digital use, therefore we gave it a DG designation and tweaked the multicoating; here it is and we're proud of it"?

Bigma for Olympus SLRs

Olympus users will not face any of the old/new confusion: only the New Bigma is available in the Four Thirds mount. Two questions however, remain open:

• Does a lens originally designed for a 24×36 mm frame have enough resolution for a 13×17.3 mm sensor? After all, the later needs twice the resolution of the former to fill the final image with the same amount of detail.
• Is the exit pupil and backfocus geometry suitable for the E-Series autoexposure and auto-WB circuitry? My experience with film-SLR, legacy lenses shows that these two functions tend to misbehave at wider apertures to a varying degree, depending on the particular lens model. This can be worked around, but would be not acceptable in a dedicated-mount, fully automated lens selling for $1000 or so.

The main goal of this article is to provide answers to these questions. This will be done in a qualitative way: no resolution targets or MTF responses; just image samples, subjectively judged. I will be also including a few comparisons against the mid-priced Olympus 14-54 mm zoom at 50 mm, and the budget Olympus 40-150 mm zoom at 50, 100, and 150 mm, just to know in which ballpark to place the Bigma.

Specifications

As a reminder, let me walk you through full specifications, mostly as given by Sigma, with my annotations wherever I felt they were necessary.

• Focal length range: 50-500 mm (EFL of 100-1000 mm when used on a Four Thirds camera).
• Maximum aperture: from F/4.0 at 50 mm to F/6.3 at 500 mm;
• Minimum aperture: F/22 at all focal lengths;
• Minimum focusing distance: from 1 m (wide) to 3 m (tele);
• Maximum magnification: 1:5.2 (unclear at what focal length);
• Filter thread: front, 86 mm;
• Dimensions: 95×219 mm (diameter×length);
• Weight: 1.84 kg (close to 4 lb), but Sigma lens table specifies 1.65 kg;
• Optical construction: 20 elements in 16 groups; four elements use low-dispersion glass;

Note that in addition to a huge maximum EFL, the lens offers a very wide 10:1 zoom ratio. While this would be worrisome for a wide-to-tele lens (unavoidable compromises in optical quality, like in most EVF cameras), here the short end of the range is well longer than the "normal" focal length, so this may be not so painful. On the other hand, the 100 mm EFL is much more often used, so this will make lens changes much less frequent if you are not carrying two bodies.

Who needs this lens

With long (narrow-angle) lenses becoming more available for digital cameras than they were for 35-mm film ones, we can witness more unexperienced photographers using them, and usually with not-so-satisfactory results.

The Bigma will be no different here. We have to remember that a 1000 mm EFL lens is not something for a general use. While it will allow to bring closer distant subjects, and to isolate them with limited DoF, it requires more attention when shooting. (If you are not sure what DoF, or Depth of Field is, and on what it depends, you certainly are not ready for a long lens. Not yet.)

First of all, the depth of field is very limited. For example, when shooting wide open at F=500 mm and with the main subject 10 meters away, the DOF extends just by one centimeter or so ahead and beyond the focused distance. Expect to have lots of badly-focused pictures.

Second, any camera shake will be greatly exaggerated with this focal length. You have to use faster shutter speeds to avoid camera shake with longer focal lengths; for 500 mm, 1/1000 s is a reasonable limit — unless you have a steady hand and a good shutter release technique (but remember, this mama is quite heavy, so your hands will be tiring fast). Of course, a tripod is recommended here; the heavier the better.

Third, under less-than-ideal weather conditions the atmospheric haze may become objectionable, especially if the lens is used for subjects 200 meters or more away. This is in addition to lower contrast, usually a fact of life with longer lenses.

Last but not least, the perspective provided by long lenses is not suitable for all objects; it is greatly compressed along the lens axis. This may be fine for single subjects isolated out of the background, or as a special effect (the often-overused shot of cars sitting on top of each other on a crowded highway), bot not for a general use. It is like writing your emails in all caps.

If you remain undeterred, you have also to remember that the longer focal lengths will come useful in only a few applications, with wildlife and field sports coming first to mind. For anything else, a shorter tele zoom (like the inexpensive but very nice 40-150 mm ZD from Olympus) will serve you much better.

Still want to buy a Bigma? Be prepared to shoot a lot, and to reject a great majority of frames. Of the remaining ones, some may be real keepers. Consider yourself warned.

Samples

I still don't have this lens. It appeared once or twice at B&H or Adorama, only to be sold out within a day.

With bird and wildlife photography being the main use to which I'm planning to put this lens, I'm not really in a hurry to get it; I will really need it only in May or so (in the meantime I got the 2.0/50 Macro, as it covers more of my needs). Therefore be patient; when I actually get the Bigma, I'll be able to write more about it.

References

• Some good samples by LightRules showing the New Bigma in the best light;
• Animal shots done with the Old Bigma and a Canon 300D (Digital Rebel) on a Dutch community site — just to make you salivate...