Univex SB-900 user manual D–22, ISO sensitivity factors, Guide number GN at ISO 100; m/ft

D

Flash modes and functions

Determining the aperture, flash output level and shooting distance

In Distance-priority, Manual and Repeating flash modes, use the guide number table and the following equation to calculate the aperture, flash output level, and shooting distance to obtain the correct exposure.

•The guide number (GN at ISO 100; m/ft) indicates the amount of light generated by the flash.

•The larger the number, the greater the flash output.

ISO sensitivity factors

For sensitivities, multiply the guide number by the factors shown in the table below.

ISO	25	50	100	200	400	800	1600	3200	6400
Factors	0.5	0.71	1	1.4	2	2.8	4	5.6	8

Guide number (GN at ISO 100; m/ft)

The table below shows the guide numbers while using the standard illumination pattern when the SB-900 is mounted on a Nikon FX format camera.

• For others, see “Specifications” (kF-18).

Flash							Zoom position (mm)
output		14mm		17	18	20	24	28	35	50	70	85	105	120	135	180	200
level	WP +	BA	WP
	BA
1/1	13/	16/	17/	22/	23/	24/	27/	30/	34/	40/	44/	47/	49.5/	51/	51.5/	54/	56/
	42.7	52.5	55.8	72.2	75.5	78.7	88.6	98.4	111.5	131.2	144.1	154.2	162.4	167.3	169.0	117.2	183.7
1/2	9.1/	11.3/	12/	15.5/	16.2/	16.9/	19/	21.2/	24/	28.2/	31.1/	33.2/	35/	36/	36.4/	38.1/	39.5/
	29.9	37	39.3	50.9	53.1	55.4	62.3	69.6	78.7	92.5	102.0	108.9	114.8	118.1	119.4	125.0	129.6
1/4	6.5/	8/	8.5/	11/	11.5/	12/	13.5/	15/	17/	20/	22/	23.5/	24.7/	25.5/	25.7/	27/	28/
	21.3	26.2	27.9	36.1	37.7	39.3	44.3	49.2	55.8	65.6	72.2	77.1	81.0	83.7	84.3	88.6	91.9
1/8	4.5/	5.6/	6/	7.7/	8.1/	8.4/	9.5/	10.6/	12/	14.1/	15.5/	16.6/	17.5/	18/	18.2/	19/	19.7/
	14.8	18.8	19.7	25.3	26.6	27.6	31.2	34.8	39.3	46.3	50.9	54.5	57.4	59.0	59.7	62.3	64.6
1/16	3.2/	4/	4.2/	5.5/	5.7/	6/	6.7/	7.5/	8.5/	10/	11/	11.7/	12.6/	12.7/	12.8/	13.5/	14/
	10.5	13.1	13.8	18.0	18.7	19.7	21.9	24.6	27.9	32.8	36.1	38.4	40.4	41.7	42.0	44.3	45.9
1/32	2.2/	2.8/	3/	3.8/	4/	4.2/	4.7/	5.3/	6/	7/	7.7/	8.3/	8.7/	9/	9.1/	9.5/	9.8/
	7.2	9.2	9.8	12.5	13.1	13.8	15.4	17.4	19.7	23.0	25.3	27.2	28.5	29.5	29.9	31.2	32.1
1/64	1.6/	2/	2.1/	2.7/	2.8/	3/	3.3/	3.7/	4.2/	5/	5.5/	5.8/	6.1/	6.3/	6.4/	6.7/	7/
	5.2	6.6	6.9	8.9	9.2	9.8	10.8	12.1	13.8	16.4	18.0	19.0	20.0	20.7	21.0	21.9	23.0
1/128	1.1/	1.4/	1.5/	1.9/	2/	2.1/	2.3/	2.6/	3/	3.5/	3.8/	4.1/	4.3/	4.5/	4.5/	4.7/	4.9/
	3.6	4.6	4.9	6.2	6.6	6.9	7.5	8.5	9.8	11.5	12.5	13.5	14.1	14.8	14.8	15.4	16.1

•BA: With the Nikon Diffusion Dome attached

•WP: With the wide-flash adapter in place

D–22