Canon 550EX manual Guide No, 121

Specifications

● Guide No.

[Normal Mode]										(At ISO 100 in meters)
Flash Coverage (mm)		17	24	28	35		50			70		80	105
Normal (full) Flash Guide No.		15	28	30	36		42			46		50	55
Quick Flash			Same as for manual flash from 1/2 to 1/6.
	1/1	15	28	30	36		42			46		50	55
	1/2	10.6	19.8	21.2	25.5		29.7			32.5		35.4	38.9
	1/4	7.5	14	15	18		21			23		25	27.5
Manual Flash Guide No.	1/8	5.3	9.9	10.6	12.7		14.8			16.3		17.7	19.5
	1/16	3.8	7	7.5	9		10.5			11.5		12.5	13.8
	1/32	2.7	4.9	5.3	6.4		7.4			8.1		8.8	9.7
	1/64	1.9	3.5	3.8	4.5		5.3			5.8		6.3	6.9
	1/128	1.4	2.5	2.7	3.2		3.7			4.1		4.4	4.9
[High-Speed Sync (FP Flash) ]
Shutter Speed				Flash Coverage (mm)
	17	24	28	35		50			70		80		105
1/125	10.6	19.8	21.2	25.2		29.7		32.5			35.4		38.9
1/160	9.4	17.5	18.8	22.5		26.3		28.8			31.3		34.4
1/180	8.8	16.5	17.7	21.2		24.7		27.1			29.5		32.4
1/250	7.5	14.0	15.0	18.0		21.0		23.0			25.0		27.5
1/320	6.6	12.4	13.3	15.9		18.6		20.3			22.1		24.3
1/350	6.3	11.8	12.7	15.2		17.7		19.4			21.1		23.2
1/400	5.9	11.1	11.9	14.2		16.6		18.2			19.8		21.7
1/500	5.3	9.9	10.6	12.7		14.8		16.3			17.7		19.4
1/640	4.7	8.8	9.4	11.3		13.1		14.4			15.6		17.2
1/750	4.3	8.1	8.7	10.4		12.1		13.3			14.4		15.9
1/800	4.2	7.8	8.4	10.1		11.7		12.9			14.0		15.4
1/1000	3.8	7.0	7.5	9.0		10.5		11.5			12.5		13.8
1/1250	3.4	6.3	6.7	8.0		9.4		10.3			11.2		12.3
1/1500	3.1	5.7	6.1	7.3		8.6			9.4		10.2		11.2
1/1600	3.0	5.5	5.9	7.1		8.3			9.1		9.9		10.9
1/2000	2.7	4.9	5.3	6.4		7.4			8.1		8.8		9.7
1/2500	2.4	4.4	4.7	5.7		6.6			7.3		7.9		8.7
1/3000	2.2	4.0	4.3	5.2		6.1			6.6		7.2		7.9
1/3200	2.1	3.9	4.2	5.0		5.9			6.4		7.0		7.7
1/4000	1.9	3.5	3.8	4.5		5.3			5.8		6.3		6.9
1/5000	1.7	3.1	3.4	4.0		4.7			5.1		5.6		6.1
1/6000	1.5	2.9	3.1	3.7		4.3			4.7		5.1		5.6
1/6400	1.5	2.8	3.0	3.6		4.2			4.5		4.9		5.4
1/8000	1.3	2.5	2.7	3.2		3.7			4.1		4.4		4.9

(Multiply by 3.3 to convert to feet)

121