Flash Concepts

  • Guide Numer = F stop x Flash-to-Subject Distance in foot unit at ISO 100 for a correct Exposed photo, regardless shutter speed (although higher shutter speed like 1/4000 should be taken in consideration, since flash is around 1/4000-1/20000 speed for generic flashes)
  • sun is a a ambient light, with constant power at within the shooting area and covering any focal length coverage (angle of illumination)
    • at ISO 100, f16, you can adjust sun power contribution to photo with shutter speed
      • at bright midday, 1/125s give correct ambient.
    • at ISO 100, f16, imagine your subject at 5 feet (1.5m) away back facing sun (lacking of sun light power contribution)
      • to make your subject correct exposure, you need f number 16 x 5 = GN 80 flash light
GN w default header
1200Ws GN110 G Q1200DII(2280): Model light 150W, 4.2kg
800Ws GN90 G Q1200DII(1880): Model light 150W, 3.7kg
600Ws GN76 G Q600DII (1280): Model light 150W, 2.8kg
400Ws GN65 G Q400DII (1000): Model light 150W, 2.66kg
250Ws GN48 G ST250 (370): Model light 75W, 1.1kg
600Ws GN87 AD600pro (4900 TTL): Model light 38W, hss, li-on 360s, color tmp lock, 3kg
600Ws GN87 AD600 (2700 M, 3900 TTL): Model light 10W, hss (trigger for M), li-on, 500s, 2.65kg
360Ws GN80 (AD-S2 28mm) AD360II (2700, li-on 450s): TTL, hss, 800g
360Ws GN80 (AD-S2 28mm) AD360 (2200, li-on 450s): hss w TTL trigger, 800g
200Ws GN60 (28mm) AD200 (1900, li-on 500s): TTL, hss, 560g
~60Ws GN60 (200mm) V860II (890, li-on 650s), TT685(550, AA 230s): TTL, hss, 20-200, , 540g
~60Ws GN60 (200mm) V850II (590, li-on 650s), TT660 (330, AA 230s): hss w TTL trigger, 20-200, , 500g
  • guide numbers are derived from actual out put of the flash unit.
    • Guide Number often used on speedlight/flash, those small portable off camera flash lights, about light intensity on its subject when it flashes (like GN20, GN35, GN56), normally at their max zoom focal length/ narrowest angle of illumination
    • of course, when you change them to cover wider focal length/angle of illumination, the GN fail down quickly
  • Watt-seconds is a measure of potential energy stored in flash units capacitors
    • Ws often used on monolight/studio flash/strobe(on battery or power cable), those big lights sitting on heavy light stand. about the max Energy stored in its capacitor for each shot. (like 500Ws, 600Ws, 800Ws)
  • as GN number is based on conditions like
    1. reflector or diffuser in use
      • which affect light spread angle (focal length on zoom head or reflector/angle of illumination)
      • which also affect efficiency of light final output
    2. ISO setting
  • As hotshoe flash is like all in one package, the header/default modifier built-in is known, so GN is given at that condition;
  • While Big Lights are given without header, and bulb only, with different headers/modifiers on them, GN changes differently,
    • so normally at given header/reflector on it, it can provide a GN value.

Thus converting the potential energy (Ws) stored in the capacitors to actual light output (GN) depends on given energy conversion efficiency, header's angle of illumination and light reduction rate

video ref: (small vs big light)


  • DC power is defined in terms of W = 1V*1A, for a battery or battery pack to holds 4000mAh (a phone like battery), while maintaining voltage of a normal lithium cell, that is 3.7V,
    • thus results 4000 x 3.7 / 1000 = 14.8 Wh
  • given phone consume at 0.3 watt, it can last 14.8/0.3 = 49 hour
  • Lithium-ion battery max capacity allowed on plane is 100Wh per battery
  • Same Type of battery (same chemical type like lithium ion, alkaline cell, NiHN cell) are mostly operating at same voltage, so they are normally compared in mAh, since Wh = mAh x V / 1000 and (V / 1000) is same for same type battery
    • same type battery's Nominal Voltage is : midpoint between fully charged and full discharged based on 0.2C discharge.
  • 20000mAh power bank (given li-on at 3.7V) is 20000mAh x 3.7V / 1000 = 74Wh, under 100Wh limit.

Flash review online

Flash Spec
recycle time
max shots before heat stop
battery type and battery max shots
remote trigger
godox trigger
xpro (388, CNSF) ttl, hss, remote manual 6 row display, 2xAA triggering without receiver supported:
AD600, AD360II, AD200, v860II, v850II, TT685, TT600, skII, dpII
x1t (220, NCSFO) ttl, hss, remote manual 3 row display, hotshoe
xt32 (220, CNS,G) hhs, remote manual 2 row display
xt16 (200) remote manual require receiver

YongNuo Flash system vs Godox flash system

Manual flash review

Godox AD600BM:

Godox Smart 300SDI

  • cable plug type studio flash, with sync cord, optical sensor, 75W modelling lamp, buzz. 300W

| smart 300SDI (90) | 75w lamp | 300w |

ms200 2.4G (-169) 150w lamp 200w 1/32-1/1 1/2000 - 1/800, no hss? 1.3kg
ms300 2.4G (100-180) 150w lamp 300w 1/32-1/1 1/2000 - 1/800, no hss? 1.3kg
sk300ii 2.4G (-239) 150w lamp 300w 40s, 1/16-1/1 1/2000 - 1/800, no hss 1.9kg
sk400ii 2.4G (110-249) 150w lamp 400w 40s, 1/16-1/1 1/2000 - 1/800, no hss 2.1kg


(all X system)

  • DP = Digital Pioneer
ranking by features option
MS - 2019 200W, 300W compact, entry level bowen+umbrella hole, lcd, 1/2000-1/800, 0.1-1.3s, 1/1-/32, 150w modeling light, 2.6kg
DSII,DEII - 2017 300w, 400w normal, 1s recycle bowen+umbrella hole, lcd, 1/2000-1/800, 0.3-1s, 1/1-/32, 150w modeling light, 3.6kg
GSII - 2017 200w,300w,400w like above but with brief case like handle bowen+umbrella hole, lcd, 1/2000-1/800, 0.3-1s, 1/1-/32, 150w modeling light, 2kg
SKII - 2017 300w,400w popular entry level bowen+umbrella hole, lcd, 1/2000-1/800, 0.1-1s, 1/1-/16, 150w modeling light, 1.9kg
DPII - ? same as DPIII, but 1/1-1/16, slower recycle
DPIII - 2019 400,600,800,1000 mass power range, 1/64, better build, 1s bowen+umbrella hole, lcd, 1/2000-1/800, 1s, 1/1-/64, 150w modeling light, 2.5-3kg
QSII - 2017 400,600,800,1200 top 2nd bowen+umbrella hole, lcd, 1/2000-1/800, 0.3-1.5s, 1/1-/32, 150w modeling light, 2.7-4.3kg
QTII - 2017 400,600,1200 top, metal build, high speed sync bowen+umbrella hole, lcd, 1/23k-1/192, 0.05-.7-.9s, 1/1-/128, 150w modeling light, 2.9-4.2kg

Flash Meter

Flash Techniques

Flash in situation

  1. built-flash usage: (demo of ambient and flash power)
  2. outdoor flash fill

Some rule:

  • Aperture for control Flash input
    • Smaller aperture, less Flash (< f8)
    • Large aperture, more flash (like f2)
  • Shutter speed for control Ambient input
    • Longer shutter, more ambient (> 1/30s)
    • Short shutter, less ambient (>1/160s)

Flash shots and Photoshop

Lighting Study

  • software:


Quick discuss about Flash equipment

Softbox List and Types

Remote Flash Trigger and High Speed Sync supported Trigger


  • for cactus V6ii triggers, make sure get the latest firmware update first, as it support better with each update. and the update happens quite frequently and operation is different each year in update.
  • check compatible list:
  • also, turn camera and flash on first, then turn on the triggers for auto detect to work properly

Most brands Flash brand and accessory brands, like Yongnuo, Godox, have dedicated high speed sync supported trigger for Canon, Nikon, Sony cameras. while Cactus V6ii trigger provides all-in-one hss trigger that support all brands of cameras and flash through TTL flash signal through its internal command translation.

Note: some cameras will not trigger or pass flash trigger signal if no TTL pin communication found, also some time cameras will stop shutter go higher than 1/180s roughly if it got no information that the flash support HSS; Thus cactus V6ii trigger sit on camera acts like a flash support HSS to allow triggering signal happen, and pass to other trigger or its pass-through hotshoe.

  • Nikon camera will send signal to hotshoe at any speed even without TTL pin
  • Pentax camera will require TTL pin to decide whether hotshoe signal sending or not at higher speed than normal sync speed

Remote Flash Trigger, aka radio trigger, are spec with

  • radio frequency
  • channel choices
  • control groups support
  • TTL support
  • power control and zoom control support\
  • has a hotshoe for stacking
  • AA or AAA or other battery type used

Cactus V6ii Trigger and Pentax Cameras

  • Note: K-01 is not supported by V6ii for HSS, but can sync below 1/160s
Setup on Camera Hotshoe (setting) under Flash Hotshoe (setting) Tested by me
Pentax camera + Pentax AF540FGZ off camera cactus v6ii in TX (P cam, P flash) cactus v6ii in RX (P flash) > AF540FGZ HSS, PTTL, remote power control tested
Pentax camera + Godox AD360 off camera cactus v6ii in TX (P cam, N flash) > Godox FT-16 Godox FTR-16 > Godox AD360 HSS when turned on AD360 manually, remote power control on FT-16 (video) tested
Pentax camera + Godox AD360 off camera cactus v6ii in TX (P cam, N flash) > Godox X1T-N Godox XTR-16 > Godox AD360 HSS when turned on AD360 manually, remote power control on X1T-N not tested
Pentax camera + Godox AD360 on camera cactus v6ii in TX (P cam, N flash) > Godox AD360 - HSS when turned on AD360 manually tested
Pentax camera + Godox AD360II off camera cactus v6ii in TX (P cam, N flash) > Godox X1T-N (manual) Godox AD360II HSS automatically, remote power control on X1T-N (ref: link, link2)
Pentax camera + Godox AD600BM off camera cactus v6ii in TX (P cam, N flash) > Godox FT-16 Godox FTR-16 > Godox AD600BM usb port HSS when pressed on HSS button on AD600BM, remote power control on FT-16 tested
Pentax camera + Godox AD600BM off camera cactus v6ii in TX (P cam, N flash) > Godox X1T-N Godox X1R (2.5 to 3.5 cable) > AD600BM sync port HSS when pressed on HSS button on AD600BM, pressed on Wireless button to remote power control from X1T-N tested
Pentax camera + Godox AD600BM off camera cactus v6ii in TX (P cam, N flash) > Godox X1T-N cactus v6ii (3.5 to 3.5 cable) > AD600BM sync port HSS when pressed on HSS button on AD600BM, pressed on Wireless button to remote power control from X1T-N ref
Pentax camera + Canon e-ttl flash off camera cactus v6ii in TX (P cam, C flash) cactus v6ii in RX (C flash + flash profile) > Canon EX flash HSS, remote power control (ref: link)
  • Out of Sync issue: as different cameras and flash have different timing between when to flash when to open shutter, a proper setting of camera and flash need to set correctly to make sure shutter and flash timing in sync. like for that AD360, a Nikon flash mode is set to make sure flash flashing at time Pentax camera open shutter. Anyway, you need to check it case by case for different flash or trigger combo.
  • High Speed Sync is a Flash fire mode for faster shutter speed above 1/125 or higher,
    • sometimes high shutter speed like 1/500s, 1/1000s, 1/2000s, 1/8000s,
    • and during that high speed duration, the shutter curtain only partially open to achieve fast shutter
    • also during which the Flash fires multiple rapid relative less powerful flashes,
    • to extend the entire flashing illumination duration like 1/125 seconds, so that providing a constant lighting, as a single flashing only last extremely short compare to shutter speed for roughly 1/320s to 1/40,0000s depends on full power to smallest power

  • as you can also see,
    • the slower “high speed shutter” like 1/500s, can get more exposure time from same flash shot
    • the higher “high speed shutter” like 1/8000s, get less exposure time from same flash shot
    • a single flash at full power last “relatively more time” like 1/320s, so shutter slower than 1/320s can see the whole range of illumination from a single flash shot
    • a single flash at lowest power last “extremely short time” like 1/40,000s, so highest shutter like 1/8000s is considered “relatively long time” for it, thus the whole shutter open time range can not receive illumination as the partial open area traveling up to down. thus multiple “extremely short time” required.
  • Power Sync is basically normal flash shot at relatively full power or near full power to achieve longer illumination duration, like high speed sync.
    • most standard flash (even w. no HSS support) with built-in or attached optical slave sensor can achieve “Power Sync” by triggered from main master flash shot
    • of course, the main master flash must support sync with camera's shutter at high speed, either in HSS mode or “Power Sync”
    • note, some TTL supported master flash may do a pre-flash for metering before actual exposure flash shot, thus, the triggered slave flashes need to set a delay time or in its slave mode that ignore first flash. (S2 mode for most flash)
    • of course, if a single full power shot last 1/320s, then camera shutter speed must be higher than 1/320 to stay within the 1/320 time frame to enjoy full illumination and avoid black-out ending in upper/lower part of image.
  • Forced HSS (like in AD360) is a HSS mode that get triggering signal from master flash optically instead from camera TTL information signal. it is like a slave mode but will fire multiple shots as HSS mode do, once optically triggered or signal triggered from a trigger.
  • in custom menu > Bracketing and Flash > Flash sync speed > 1/320 Auto FP for nikon flash, 1/250 Auto FP for other brand flash (it will enable you to use 1/8000 than it writes)

DIY off-camera Flash cord

Other DIY photo guide

  • photowiki/flash.txt
  • Last modified: 2023/05/21 14:15
  • by ying