Not your father’s superzoom

Background:

The Sigma 20-200mm zoom on the Leica SL2-S.

The Sigma 20-200mm f/3.5-6.3 DG Contemporary Lens in L-Mount easily qualifies as a ‘superzoom’, with its 10:1 zoom range. Boasting no fewer than 18 elements in 14 groups – a testimony to computer-aided design – it weighs in at a modest 19.4 ounces. Four of those elements are aspherical. This relatively low weight is attributable to Sigma’s use of polycarbonate plastics for much of the chassis, in lieu of the typical construction of Leica SL lenses which come in all metal construction. The bayonet mount is stainless steel and the innards are made of light alloys. It’s no secret that Sigma’s optical designs find their way into many Leica branded L mount lenses, where metal is added and the price is hoiked by 50-100%. German labor costs, you understand.

Optics:

Generous use of aspherical surfaces – outlined in red.

FLD? Standing for ‘F’ Low Dispersion, the material is claimed to have performance equivalent to fluorite glass, but at a more affordable price. Its optical characteristics apparently allow excellent correction for residual chromatic aberration, while its lower density compared to traditional optical glass allows lighter lenses.

SLD? Special Low Dispersion glass enables the mass production of high-quality lenses; it’s a material which reduces optical aberrations at lower cost than fluorite glass.

Macro capability:

The Sigma 20-200 is available in Sigma branding only and, as far as I can tell, is the L mount full frame lens with the widest zoom range. Not content with making a lens with an extraordinary zoom range, Sigma added a macro capability with the lens focusing down to half life-size in the 20-85mm zoom range. At 200mm the maximum reproduction ratio is 1:3, or one-third life size. At 20mm the lens to object distance is really too small but at 85mm it makes for a very useful macro lens and even at 200mm the macro capability is substantial.

Feel and controls:

The focus ring, which is an electronic ‘fly by wire’ design, not a mechanical one, is butter smooth. There are no focus stops, just continuous rotation, and the lens’s length does not change as it is focused. It feels metallic.

The zoom ring, rather counterintuitively, has to be rotated counterclockwise to lengthen the focal length. One adapts quickly. It’s a tad stiffer than I would ideally like but expect it will loosen up with use. It feels rubberized with somewhat coarser fluting than on the focus ring.

Despite the extensive use of plastics for the focus and zoom collars the overall feel of the lens is that of a high quality optic. Amazingly, when fully extended at 200mm (7.5″ lens length) there is absolutely no play in the extended barrel. Well done, Sigma!

Autofocus and lens switches:

Until now all my lenses for the Leica SL2-S have been either Leica M mount lenses used with Leica’s competent adapter, or old manual focus Nikkors used with an inexpensive aftermarket Nikon F to L mount adapter. The Sigma is my first autofocus lens for the SL2-S. Mine was purchased new from B&H and came with a pouch, lens hood and front and rear caps. The filter mount size is 72mm. There are two switches on the lens – AF/MF and a zoom lock at 20mm. While my sample does not extend under gravity wear and age may yet make the lock switch useful. The lock can be unlocked using the switch or with a twist of the zoom ring. Nice. The diaphragm has nine blades.

The lens does not maintain focus as it is zoomed, but AF makes this a non-event. I doubt the AF is fast enough for sports photography but for my intended uses – street snapping and travel – it’s fast enough. The AF motor is silent.

Manual focus:

Switch to MF and a touch on the focus collar brings up a magnified image in the finder of the SL2-S making nailing focus trivial. (This feature can be turned off in the SL’s controls). Touch the shutter release to revert to normal magnification in the EVF. Beautifully implemented.

The manual focus option is intriguing, Turn the focus ring rapidly and you get from infinity to closest focus in a half turn of the ring. However, turn the focus collar slowly and it takes a full two turns to span the focus range. This is especially handy for focus stacking of multiple macro images where one would usually use a rack to drive the whole camera + lens assembly to and from the subject, as using the focus collar the minute focus changes required between images are almost impossible to apply using a lens with a regular focus collar. With the fine focus changes possible with slow movements of the Sigma’s collar focus stacking is readily achieved. A brilliant design of ‘fly-by-wire’ electronic focusing.

The Contemporary lens line:

Sigma has three lens lines. The Art series lenses are mostly large aperture and bulky, with high optical quality and fixed maximum apertures in the zooms. I owned the 35mm f/1.4 and it remains the sharpest lens I have used. The Sport series mainly comprises long zooms and fixed focus optics, with the zooms having a fixed maximum aperture. Finally, the Contemporary series, which includes the 20-200mm zoom, is the budget line and boasts 14 full frame primes and four zooms, two of which have fixed maximum apertures – the 16-28mm and the 28-70mm, both f/2.8. That’s not the case here where the maximum aperture at 20mm of f/3.5 falls to f/6.3 (2 stops slower) at 83.3mm and up. I suppose that compromise keeps weight and bulk down. Contrast that with my current Nikon superzoom, the 28-300mm AF-S Nikkor G, whose apertures range from f/3.5 to f/5.6, with a similar 10:1 or so zoom range. With the Sigma you get the far more useful 20mm at the wide end, sacrificing 100mm off the long end. That works for me. Sigma claims the lens is weather sealed, with seven internal seals, and there is also an external rubber O-ring on the bayonet mount.

Country of origin:

From the booklet included with the lens.

Image stabilization:

There is no image stabilization in the lens, but the Leica SL2-S’s IBIS does the trick. Also, in the L mount version distortion correction – barrel and wave at the wide end and pincushion at the long one, along with substantial vignetting at the shorter focal lengths – is done in camera. That’s a smart approach which further frees up the designer and likely reduces weight and bulk. See below for examples of how well this works.

Weight and bulk:

And how do weight and bulk compare between the SL2-S with the 20-200 and the Nikon D800 with the 28-300mm? Both are fitted with Upstraps, SDHC cards, a lens hood and a UV protective filter:

The Sigma on the Leica SL2-S.

Nikon D800 with the 28-300mm AF-S zoom.

While the Sigma lens weighs just over one pound the heavy weight of the mirrorless SL2-S rather offsets the weigh savings compared with a conventional, flapping mirror DSLR.

Aperture control:

There is no aperture setting ring on the lens. Apertures are changed with the rear thumbwheel on the camera’s body.

Automatic distortion correction:

The Leica SL2-S automatically applies in camera distortion correction, and it is spectacularly good, especially when the peculiar waveform + pincushion distortion of the native lens is taken into account at the shorter focal lengths, not to mention the significant corner vignetting at those focal lengths. Look at the parallelism of the top of the bookcase with the edge of the frame, and note the absence of any vignetting:

At 20mm.

At 200mm.

Turn on ‘Enable Profile Corrections’ in LRc and the results are ghastly – this setting would only be used with cameras which do not provide automatic distortion correction. The reason they are so poor is that profile correction is being applied twice – once in the camera and then again in LRc. What these images disclose is just how severe the distortion and vignetting of the native lens really are, and how perfectly the Leica corrects them. LRc has the lens correction profile for the Sigma lens – I believe it would have to be used with certain Sony mirrorless bodies which do not apply in camera distortion and vignetting correction, for the Sony E-mount version of this lens.

At 20mm with LRC’s ‘Enable Profile Corrections’ enabled.

At 200mm with LRC’s ‘Enable Profile Corrections’ enabled

Definition at full aperture:

I’l publish regular street snaps in a later post; meanwhile these are at full aperture at the extremes of the zoom range:

At 20mm, f/3.5.
Click the image for a larger version.

At 200mm, f/6.3.
Click the image for a larger version.

Best use:

This is a perfect travel lens. It’s also excellent for Macro – see below. One lens which does it all. If you want lightning fast AF for sports photography, or need large apertures for poor light or shallow depth-of-field look elsewhere.

A quick macro example:

Using the ‘slow focus’ function of the focus ring (see ‘Manual focus’, above) I exposed 36 images of the wild flower using MF:

Lesser Burdock. 50% crop of the original image.
Click the image for a larger version.

The ISO was set at 100, and the Sigma’s aperture at f/16. Focal length was 129mm. Lighting was from three strobes. The result is a focus stacked image using 36 differentially focused images, stacked using Helicon Focus. I think you may agree the definition is half decent.

More in Part II.

A special lens – when properly tuned.

For an index of all Leica-related articles click here.

The 135mm f/4 Elmar on my Leica M10.
The auxiliary finder is for a 21mm lens.

I profiled the 135mm f/4 Leitz Elmar lens here. Read that piece to learn how to properly align your rangefinder to have this lens perform at its best. It’s a critical step which, if avoided, will have you blaming an excellent optic for unsharp results.

A 2mm Allen wrench is used to adjust the cam follower for optimum focus.

Explanation of which direction to turn the Allen screw adjuster: If the sharpest point in the LR magnified image is further than where you focused, then the focus point must be brought nearer, meaning you turn the Allen screw adjuster away from you, with the camera resting as in the above image. If the sharpest point in the LR magnified image is nearer than where you focused, then the focus point must be set further away, meaning you turn the Allen screw adjuster towards you, with the camera resting as in the above image. Take it easy with those adjustments – just a couple of degrees’ movement will shift the dice point noticeably.

The 135mm focal length, especially used at large apertures and/or close focus distances, is really stretching the rangefinder accuracy of the Leica M to its limit. To get the best (definition) bang for your buck I suggest that a 135mm Elmar plus a good finder magnifier beats the costlier 135mm Tele-Elmar with no magnifier, the outlays being roughly identical. What the Elmar lacks in contrast compared with its costlier successor is easily made up with a tweak or two in Lightroom. The Elmar lacks little when it comes to micro-contrast and resolution of fine details. An additional investment in sweat equity (and a 2mm Allen wrench) will see to it that your rangefinder is perfectly adjusted and that focus error will not be the cause of unsharp results.

How far is ‘infinity’ as marked on the lens? It’s much further than you might think. In the test images below, the car’s registration plate is exactly 82 yards away from the camera, whereas the roof at the top right is 125 yards distant. There is a clear difference, per the rangefinder, between 82 yards and 125 yards. At 125 yards the lens is indeed set to infinity.

Stated differently, if you want to insure that when the lens is at infinity the subject is also at infinity, your subject must be 125 yards or more distant from the camera. That’s a long way off. At 82 yards and 100% pixel peeping at full aperture the depth of field is no more than 4 feet fore and aft of the registration plate of the car in these images. That’s as good an illustration of how critical focus is with a lens this long, used with a Leica rangefinder, as I can conceive of. It also shows what an extraordinary feat of mechanical/optical engineering the Leica rangefinder is to this day, and has been since the first M3 in 1954.

Here are the test images taken at all apertures from f/4 down to f/22 – the M10’s lens code is set to ‘135mm f/2.8 Elmarit’, which is the best choice. The lens is so distortion and vignetting free that there is no need to use a lens correction profile in LRc when processing images. These images are SOOC, and I used a monopod to minimize camera shake.

Test images from f/4 to f/22. The apertures shown are incorrect.

You can view all 8 images in medium size by clicking here.

To view full size 22mb originals click here. It’s a large file so be patient when downloading. You can zoom in on these to your heart’s content.

Conclusions?

• Hard to focus correctly using the rangefinder at full aperture and/or short subject distances. Focus accuracy benefits meaningfully when used with a 1.4x finder magnifier
• No flare or distortion at any aperture.
• At f/4 the whole frame is usable and will easily make a large print with excellent resolution if focus is correct.
• Micro contrast is excellent at any aperture.
• There is little change in resolution hereafter through and including f/22. If there’s any diffraction at the smallest aperture it’s nearly impossible to see.
• Peak definition is reached at f/5.6 but there’s very little to choose between any aperture from f/4 to f/22.
• No meaningful color fringing at the edges of the frame at any aperture. The camera is coded as a Leitz f/2.8 135mm Elmarit-M which delivers the best result of the three coding options for 135mm lenses in the M10’s firmware. Absent machining the lens cannot itself be 6-bit coded unless you buy the rarer LTM version and use a 6-bit LTM-to-M bayonet adapter.
• There is no LRc lens correction profile available so I use the one for the 135mm f/3.4 Apo-Telyt-M. The only noticeable difference is correction of extremely minor pincushion distortion, but it’s not really necessary other than in architectural photos taken straight on.

By the way, disregard the f-stop data in the EXIF information. The M10, even with 6-bit coding adapter, does a poor job of estimating the aperture used. (There is no electrical or mechanical link between the lens’s aperture setting and the camera, so Leica estimates the aperture based on the shutter speed and ISO used). Go by the file names, moving the decimal point in the last three digits one place to the left to see the aperture used. So, for example ‘110’ means f/11.

So which is better – the Canon 135mm f/3.5 LTM at $150 shipped from Japan or the Leitz 135mm f/4 Elmar at $260 shipped within the US? Both are bargains, but the Elmar is clearly better at all apertures and requires no amendments to the focus cam to properly align with the cam follower in the camera’s throat. There is no flare at any aperture and micro contrast is notably better at all apertures. Is the difference night and day? No. But if you make selective crops and big prints the Elmar is the one to choose, at a $110 premium, and abundantly available from domestic sellers. In summary, this 1960 optic is outstanding in every way. (Made from 1960 through 1965, the Elmar was replaced by the physically shorter but heavier Tele-Elmar. Most tests suggest the Tele-Elmar offers little optical improvement and, boy, it has an appearance only a mother could love).

Here’s the Elmar at its very best:

Click for a bigger version. Check the definition in the glass
globe and wall stickers in the big version.