Canon RF 100-400mm F5.6-8 IS USM Review: The Cheapest Way to 400mm on Canon Mirrorless
Most telephoto zooms that reach 400mm cost thousands and weigh well over a kilo. The Canon RF 100-400mm F5.6-8 IS USM costs about $650 and weighs around 635 grams. It’s light enough to carry on a hike, cheap enough to buy on a whim, and a lot sharper than the price suggests.
That’s why it became one of Canon’s most popular RF lenses. It’s the default “first long lens” for R50, R10, R8 and R6 Mark II owners who want to try birds, kids’ sports or airshows without committing serious money.
The tradeoff is right there in the name: f/8 at the long end. That’s slow, and it matters. But Canon’s newer bodies focus well in dim light and clean up high ISO better than ever, and that’s what makes a slow lens like this usable.
Video review: Gordon Laing
Sharper than it should be
In good light it’s impressively sharp, including at 400mm wide open. It doesn’t match Canon’s white L telephotos for contrast and corner detail, but for its price the gap is small. On an APS-C body like the R7 or R10 it gives the field of view of a 640mm lens, a reach that used to belong to big, expensive glass.
It also focuses fairly close, with a maximum magnification of about 0.41x at 400mm. That makes it a handy lens for butterflies, dragonflies and flowers from a distance.
Handling and focus
The Nano USM motor focuses quickly and quietly, keeping up with eye and animal tracking on current Canon bodies. Optical stabilization is rated at 5.5 stops on its own, or up to 6 stops paired with in-body stabilization. You’ll need it at 400mm and slow-ish shutter speeds.
The lens is compact when retracted and uses a 67mm filter. It works with Canon’s RF teleconverters in the longer part of the zoom range, though at f/11 or f/16 you’ll want very good light.
The compromises
f/8 means higher ISOs early in the morning and in the evening, which is exactly when wildlife is most active. Expect noisier files in poor light, and plan to use noise reduction.
It isn’t weather sealed. There’s no tripod collar. The plastic build feels light rather than rugged. Bokeh is decent but not creamy, so subject separation depends on distance more than aperture.
Who should buy it
Beginners and hobbyists who want to try wildlife, birds, sports or airshows. Travelers who want a long lens that fits in a daypack. Anyone shooting an APS-C Canon who wants serious reach without serious cost.
If you outgrow it, Canon’s RF 100-500mm L and RF 200-800mm are the steps up, each much bigger and pricier. Many owners keep this lens anyway for light days.
For the money, nothing in Canon’s lineup gets you closer to the action.