# Sharp Zone Planner for 360° Product Spins | PhotoRobot # Sharp Zone Planner Check whether a whole product stays sharp through a full 360° spin at full sensor resolution: Focus Envelope vs rotation volume, diffraction and focus stacking. Interactive tool: enter the camera, lens, distance, product size, sharpness standard and aperture. The planner draws the setup to scale (top and side view with the angle of view), compares the rotation volume of a 360° spin with the Focus Envelope, checks diffraction and proposes focus stacking when one exposure cannot be sharp everywhere. A 3D camera view simulates the frame with physically based blur and colors the sharp, too-near and too-far zones. Example (default setup): Canon EOS R5 Mark II, 105 mm lens, 1500 mm from the sensor mark to the turntable axis, sneaker 298 × 153 × 116 mm. The rotation volume is 320 mm deep; at f/16 the Focus Envelope is 22 mm. Depth and diffraction collide. The spin needs f/229 for depth, but diffraction caps this standard at f/6.1. ## How the planner decides ### Rotation volume In a spin every part of the product passes the front and the back of the turntable. The planner treats the product as the cylinder it sweeps: radius `R = √(W² + D²) / 2` plus any off-center offset, height `H`. Seen by a camera raised by angle `θ`, that cylinder is `2R·cos θ + H·sin θ` deep along the lens axis. ### Focus Envelope The Focus Envelope is the depth band in which defocus blur stays within the sharpness standard. It uses the same thin-lens formula as our [depth of field calculator](https://www.photorobot.com/depth-of-field-calculator): `H = f²/(N·c) + f`, near `= (H − f)·s / (H + s − 2f)`, far `= (H − f)·s / (H − s)`. Focus at the harmonic mean `2ab / (a + b)` of the volume's front `a` and back `b` splits it evenly. ### Full resolution means one pixel For deep zoom the standard is strict: the circle of confusion equals the sensor's pixel pitch (4.39 µm on an EOS R5 Mark II). The f-number that covers the whole volume is then `N = f²·s·(1/a − 1/b) / (2c·(s − f))`, which close up behaves like `depth · m² / (2c·(1 + m))`: depth needed grows with magnification squared. ### Diffraction sets a ceiling Stopping down spreads every point into an Airy disk `2.44 · λ · N · (1 + m)` wide (λ = 550 nm). Once its radius passes the pixel pitch, a smaller aperture stops adding sharpness. When the depth needs a higher f-number than that ceiling, no single exposure is sharp at full resolution, and the chart shows the best compromise. ### Angle of view The cone in both drawings is what the sensor sees: `2·atan(sensor / 2v)`, where `v = f·(1 + m)` is the lens-to-sensor distance at this focus. Focused at infinity it is the catalog value `2·atan(sensor / 2f)`; close up the view narrows a little. ### Camera view The simulated frame renders a 3D model of the product (a real model at true size for most presets) and reads the distance of every pixel. A point at distance `z` blurs into a circle `f²·|z − s| / (N·(s − f)·z)` wide on the sensor, exactly the circle the Focus Envelope limits to one pixel, combined with diffraction. With the blur exaggerated, everything beyond that pixel is drawn twice its full-resolution size; without it, at 100% one screen pixel is one sensor pixel. ### Focus stacking Stacking shoots several focus slices at a sharp aperture and merges them. It restores full resolution, but each slice multiplies the exposures per frame, so a 36-frame spin quickly runs to hundreds or thousands of shots. ### Distance from the sensor or the lens In the studio you measure from the sensor-plane mark on the camera body; the optics need the distance from the lens. For a thin lens `u = s/2 · (1 + √(1 − 4f/s))`. Choose which one you entered; the difference matters most at close range. Related tool: [Depth of Field Calculator](https://www.photorobot.com/depth-of-field-calculator).