Choosing a telephoto lens usually means choosing between size, cost, and autofocus capability. The Kase 150mm f/5.6 autofocus mirror lens is trying to hit all three at once, and that's not something any lens has really pulled off before at this price point.
Coming to you from Christopher Frost, this thorough video breaks down exactly what the Kase 150mm f/5.6 actually delivers in real-world testing. Mirror lenses use internal mirrors to compress a long focal length into a much smaller, lighter body than a conventional telephoto design, and they typically cost less too. The tradeoff has always been soft image quality, bad flaring, and manual-only focus. Kase is promising to fix that last problem with built-in autofocus, which is almost unheard of in this category. Frost tests it on a Sony a7CR with its 61 MP sensor, which is about the most demanding test bed you could throw at a lens like this.
The autofocus works, but Frost is clear about its limits. It's slow and audible, and subject detection on the a7CR missed shots roughly 7 to 8% of the time. That rules it out for sports or fast action. The lens is built mostly from metal, weighs around 480 g, and includes a USB-C port for firmware updates and a weather-sealing gasket at the mount. It's available in Sony E-mount, Nikon Z-mount, Fuji X-mount, and Canon EF-mount, the latter of which can be adapted to Canon RF-mount bodies with autofocus intact. At around $650, the build quality feels solid for the money. The lens also supports Kase's magnetic filter system, which Frost clearly has some genuine affection for.
Image quality is the part of this video you really need to watch for yourself, because Frost walks through center sharpness, corner performance, crop mode behavior, flaring, distortion, and bokeh in methodical detail. What he finds isn't a surprise for a mirror lens, but there are a couple of results that may shift your expectations in one direction or the other. The distinctive donut-shaped bokeh highlights are the lens' most talked-about feature, and Frost addresses exactly when that look works and when it turns into a mess. At 150mm, it's actually easier to fill a frame with those circular highlights than it would be at longer focal lengths, which is one of the more interesting practical points he raises. Flaring against bright light is a real issue here, and the included lens hood is narrow enough that Frost flags it as only marginally useful. Check out the video above for the full breakdown from Frost.
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