Handheld at 1/4s: IBIS with the RF 15-35mm f/2.8L IS USM
The Canon R5 Mark II’s IBIS combined with the RF 15-35mm f/2.8L IS USM provides up to eight stops of combined stabilization according to Canon’s specification. In practice, on a full-frame sensor at 15mm, that means a stationary subject can be photographed sharp handheld at shutter speeds as slow as 1/4 second by a photographer who has learned to hold still. This is not theoretical. It works.
The technique is breath control and body mechanics. Before firing, exhale half your breath and hold it. Lock your elbows against your torso. The camera shake that IBIS cannot fully correct is the gross movement of your body — IBIS handles micro-tremors, not lurching. Your job is to reduce large-scale movement to the level where the stabilization system can manage the remainder.
At 1/4s in a dim interior — a cathedral, a restaurant, an underlit gallery — you can shoot at ISO 800 and f/4 and produce a clean, usable frame. Without stabilization, 1/4s handheld at 15mm would require ISO 6400 to match at a safe shutter speed, and the noise penalty on even modern sensors at ISO 6400 is visible. IBIS is an image quality tool, not just a safety net.
The limitation: IBIS stabilizes camera movement, not subject movement. Any person, flame, or moving element in the frame will blur at 1/4s regardless of how still you hold the camera. In some contexts — a crowded street at dusk, candles in a church — that subject blur is atmospheric. In others — a portrait, a product — it is a failure mode.
Shoot in RAW. The shadow latitude on R5 Mark II files is substantial, and an image that looks dark on the LCD in a dim room is often one stop of positive exposure compensation from a clean file. ETTR applies here: hold the highlights, recover the shadows in post.
Eight stops is a specification. Four stops of consistent success rate is what you earn with practice.