Many nightscape photographers find a 20mm to 24mm lens their most used focal length. While there are many models on the market, we don’t need the expense of an automatic lens with auto-focus. Lower-cost manual lenses will serve us fine. At just $240, the new no-frills TTArtisan 21mm falls nicely into that price and focal length range.
Affordable and Compact
Established in China in 2019, TTArtisan is a new name in camera lenses, specializing in manual models only for the new generation of mirrorless cameras. Their 21mm is available in versions to fit Canon RF, Leica L, Nikon Z and Sony E mounts.
The attraction of the TTArtisan is its price, especially when compared to the $900 cost of Sony’s and Nikon’s native 20mm f/1.8 lenses, or Sigma’s 20mm f/1.4 Art.
Despite its low cost, the TTArtisan 21mm offers a fast f/1.5 maximum aperture, nearly a stop faster than an f/2 lens and two stops brighter than an f/2.8 lens. Yes, few lenses will perform well when used “wide open.” However, a fast aperture is useful for providing a bright live view image to aid focusing and framing at night.
The other attraction is its compact size, at just 90mm long and 72mm wide. The lens weighs 500 grams, half the weight and nearly half the length of the 20mm Sigma Art, though similar in weight to the larger 20mm Sony G and Nikon S lenses.
Mechanics — Focusing and Aperture
Like TTArtisan’s 11mm fish-eye I reviewed earlier, the 21mm is no “plastic fantastic.” It has metal construction with a dense, well-made feel. The focusing motion is smooth, turning from 0.5 meters to infinity over about 180°.
In the unit I purchased for Canon’s RF mount, stars were sharpest with the focus set just beyond the 5 meter mark, not with the lens turned all the way to the stop at infinity. This inaccuracy makes the lens a bit of a fuss to focus at night.
The manual aperture ring has clicked indents at every half stop, with the full stops marked from f/1.5 to the smallest aperture of f/16.
The lens has no electrical contacts to the camera, so images do not record what lens or aperture was used. There is no weather sealing around the mounting flange. When fitted with the included metal screw-on hood, the lens accepts circular 72mm filters, unusual for such a wide-angle lens.
Optics — Aberrations and Vignetting
The unforgiving test of any lens is how well it performs on stars. I shot my test images using the full frame Canon R6 on a star tracker to eliminate star trails which can mimic aberrations.
I would expect aberrations when the lens is used at f/1.5, and the TTArtisan certainly has them in abundance. At the corners stars exhibited a high level of coma (flaring stars into winged seagulls) and astigmatism (elongating stars into streaks). Star images also showed colored streaking from lateral chromatic aberration (CA).
The three off-axis aberrations decreased at f/2. At f/2.8 coma and lateral CA were minimal but astigmatism remained, as it did at f/4, though stars were sharper and not bloated.
At the center of the frame, at f/1.5 stars were enlarged by spherical aberration which adds an unfocused glow around stars. Star images tightened up a lot at f/2, with some longitudinal chromatic aberration present adding a purple halo to bright stars.
At f/2.8 most of the purple CA was gone, and stars looked sharp, almost as good as they did at f/4, as slow as you might shoot with a lens like this for astrophotography.
I compared the TTArtisan 21mm to the Sigma Art 20mm, a premium lens but with a reputation for severe off-axis aberrations. The little TTArtisan, at a quarter the cost of the Sigma (albeit not an auto-focus lens as the Sigma is) actually outperformed the premium Sigma.
At f/2.8, shown here, a typical aperture for wide-angle star fields, the Sigma showed more astigmatism intruding farther into the frame than did the TTArtisan.
Where the Sigma had the advantage was in lower vignetting. While the Sigma showed a lot of darkening of the frame corners wide open at f/1.4, it brightened up considerably at f/2.8, shown here, and is very uniform at f/4.
Not so the TTArtisan. Vignetting proved to be its weakness, perhaps a consequence of its small size.
While the TTArtisan’s corners brightened as the lens was stopped down, vignetting never went away, even at f/4. The lens always exhibited a bright center and dark edges. I first attributed this to the add-on lens hood, but the vignetting was present even without the hood in place.
As I show here, vignetting can be fixed in raw processing, by applying a lens correction to brighten the corners, an adjustment that has to be dialled in manually with this lens, easy enough to do.
What is not easy to fix “in post” is the lens’s odd color gradient. In testing the lens on my Canon R6 the edges of the frame exhibited a magenta tint, an effect not present when using other lenses on the same camera. A lens-induced color gradient is rare and is the worst flaw of this lens.
When stopped down to f/2.8 the TTArtisan can be used for wide-angle Milky Way images taken on a tracker. However, the color gradient will be a challenge to overcome in processing.
At f/2, optical quality is good enough for tripod nightscapes where the fast speed will help keep exposure times short for minimizing star trailing. The off-axis aberrations will be partly masked by whatever star trailing remains, but the vignetting and color gradient will be serious problems.
At f/1.5 most images will be unusable. But I can see one redeeming application: aurora photography, where the fast aperture allows short shutter speeds to freeze the motion of active displays, and makes rapid-fire time-lapses and real-time 4K movies possible. Both are forgiving of lens aberrations. Being compact, the lens will be easy to pack for flights to northern aurora sites.
For me, the TTArtisan 21mm is first and foremost an aurora lens, as demonstrated in the opening image. Buy it for Milky Way nightscapes only if budget is a primary concern.
Plus: Compact for ease of packing; fast optics
Minus: Aberrations and uneven color; infinity focus not accurate
MSRP: $240 (for mirrorless lens mounts only)