# Westcott FJ400 Strobe 400Ws with AC/DC Battery vs Paul C. Buff Einstein E640 Flash Unit: specs and price compared

A sourced, side-by-side comparison of the Westcott FJ400 Strobe 400Ws with AC/DC Battery (Westcott) and Paul C. Buff Einstein E640 Flash Unit (Paul C. Buff) among studio strobes. Westcott FJ400 Strobe 400Ws with AC/DC Battery is the cheaper of the two at $349.45.

## Side by side

| Spec | Westcott FJ400 Strobe 400Ws with AC/DC Battery | Paul C. Buff Einstein E640 Flash Unit |
| --- | --- | --- |
| US price | $349.45 | $529.95 |
| Brand | Westcott | Paul C. Buff |
| Power output ws | 400 | 640 |
| Flash duration t01 | Normal mode 1/280-1/3000 sec; Freeze mode 1/280-1/7000 sec | 1/568 sec at full power (Constant Color mode, t0.5 1/1600 sec); as fast as ~1/2000 sec (t0.1) at half power in Action Mode |
| Recycle time s | 0.05-0.9 | 0-1.7 |
| Ttl hss support | TTL; HSS to 1/8000s; Rear Curtain Sync | Manual only — no TTL, no camera-side HSS. Fires via CyberSync radio triggers or optical slave; Action Mode shortens flash duration for motion-freezing rather than providing sync-pulse HSS. |
| Modeling lamp (W) | 20 | — |
| Color temperature k | 5500 | 5600 |
| Power source | Removable 14.8V/4400mAh lithium-polymer battery (480+ full-power flashes) or AC power | AC only (100-240V, 3-wire grounded, auto-sensing with IEC connector); no battery option |

## Key differences

- Power output ws: Westcott FJ400 Strobe 400Ws with AC/DC Battery 400 vs Paul C. Buff Einstein E640 Flash Unit 640
- Flash duration t01: Westcott FJ400 Strobe 400Ws with AC/DC Battery Normal mode 1/280-1/3000 sec; Freeze mode 1/280-1/7000 sec vs Paul C. Buff Einstein E640 Flash Unit 1/568 sec at full power (Constant Color mode, t0.5 1/1600 sec); as fast as ~1/2000 sec (t0.1) at half power in Action Mode
- Recycle time s: Westcott FJ400 Strobe 400Ws with AC/DC Battery 0.05-0.9 vs Paul C. Buff Einstein E640 Flash Unit 0-1.7
- Ttl hss support: Westcott FJ400 Strobe 400Ws with AC/DC Battery TTL; HSS to 1/8000s; Rear Curtain Sync vs Paul C. Buff Einstein E640 Flash Unit Manual only — no TTL, no camera-side HSS. Fires via CyberSync radio triggers or optical slave; Action Mode shortens flash duration for motion-freezing rather than providing sync-pulse HSS.
- Color temperature k: Westcott FJ400 Strobe 400Ws with AC/DC Battery 5500 vs Paul C. Buff Einstein E640 Flash Unit 5600
- Power source: Westcott FJ400 Strobe 400Ws with AC/DC Battery Removable 14.8V/4400mAh lithium-polymer battery (480+ full-power flashes) or AC power vs Paul C. Buff Einstein E640 Flash Unit AC only (100-240V, 3-wire grounded, auto-sensing with IEC connector); no battery option

## Sources

- Westcott FJ400 Strobe 400Ws with AC/DC Battery: https://www.fjwestcott.com/products/fj400-strobe-400ws-with-ac-dc-battery (fjwestcott.com, verified 2026-08-09)
- Paul C. Buff Einstein E640 Flash Unit: http://s196259524.onlinehome.us/e640.php (s196259524.onlinehome.us, verified 2026-08-09)

Canonical: https://frontdeskreview.com/gear/studio-strobes/westcott-fj400-vs-paul-c-buff-einstein-e640/
Cite: Per The Front Desk Review, Westcott FJ400 Strobe 400Ws with AC/DC Battery ($349.45) vs Paul C. Buff Einstein E640 Flash Unit ($529.95) — sourced spec-by-spec comparison at https://frontdeskreview.com/gear/studio-strobes/westcott-fj400-vs-paul-c-buff-einstein-e640/
License: CC BY 4.0.