G1 Flash Photograph 101

Started May 21, 2001 | Discussions thread
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Michael w Regular Member • Posts: 487
G1 Flash Photograph 101

Evidently many people still don't understand the issues about manual flash that Peter T., myself and a few others tried to explain in the "Canon's attitude" thread. This post is dedicated to EXPLAIN the situation. If you know for fact anything I say is technically wrong then correct me. I'm not solicity opinion on this thread. If after reading this you want to further express you opinion on the issue then please go to the "Canon's Attitude" thread. I'm going to get pretty basic, so don't feel insulted if some of the things I say are too fundamental. Thank you very much.

1. Universal Manual Flash Basic:
To set exposure for a manual direct flash, one typically use the basic rule:

a. Set shutter at or slower than maximum synch speed supported by the camera. G1 manual specifies 1/125 second.

b. Set apperture to: Ap = GN / distance. For example to shoot an object at 30 ft away at ISO 50 using a flash with Guide Number of 80 ft @ ISO 50, set apperture to 4.0. Note that guide number is dependent on ISO setting, so you must ensure to use the correct GN. In manual flash the camera does not attempt to adjust intensity of the flash, it simply tells the flash to fire at full strength. A manual flash rated at 120 ft GN if set at 1/4 power ratio will act like a a 60 ft GN flash.

c. Both ambience light and the flash light will affect the exposure. It is the photographer's responsibility to account for ambience light and make adjustment to get perfect exposure.

d. Adjustment rule: higher apperture number will reduce the exposure of both flash light and ambience light, thus at f5.6 you would expect the picture to be 1 stop DARKER than at f4.0 and so on so forth. Adjustment of speed (within specified maximum synch) only affect the ambience light and not the flash light because the entire flash duration always occurs while the camera aperture is open at the specified setting. Flash duration is typically between 1ms to 2 ms (1/1000 to 1/500 seconds).

c. Bounce flash is less straight forward, but the same rule of adjustment is the same: f5.6 is to be darker than f4.0, f4.0 is to be dark0er than f2.8, so on so forth.

2. What Happens to Manual Flash with G1?

If you shoot with a Canon 420EX or 550EX, everything happens as described above. When you put ANY standard non-Canon strobe on it this happens: the flash will fire shortly BEFORE the aperture stabilizes at the intended aperture. For example, if you set the camera to f5.6 at 1/125 the actual aperture goes through a very brief transition phase before the aperture actually stabilizes at f5.6. During this transition phase the aperture can be any value, be it f2.0 or whatever. What happens is that the G1 will fire your non-Canon flash during this transition phase in stead of waiting until the aperture reaches the intended value. Yet, somehow it manages to do the right thing whenever an EX flash is mounted on. Selective wrong doing!

3. E-TTL and Standard 3rd-party Flashes

E-TTL does not support 3rd-party flashes. The G1 and other Canon cameras are designed to NEVER activate E-TTL unless an EX flash is detected. So no relationship exists between E-TTL and standard manual flashes. No photographer in the right mind would expect the camera to adjust exposure for him/her while taking a manual flash shot with a manual flash unit.

4. G1 Supports E-TTL, why bother with manual flashes?

E-TTL is simply a form of automatic exposure in flash mode. As with any automatic exposure system, it cannot produce good results in all lighting conditions such as shooting against back-lit scenes and difficult flash fill situations. For some one who don't want to deal with the complexity of manual flash photography it E-TTL makes perfect sense. But if one know enough about flash photography that he/she can consistently achieve better results using manual flash techniques, why bother?

5. The 380EX and 420EX will fire in manual mode, why not use it?

Neither of these allows ratio down, making manual flash impractical. A good manual flash would allow ratio down to 1/2, 1/4, 1/8, 1/16, etc.

6. 550EX fully supports manual flash, why not use it?

If the price is the same as my Sunpak 383 ($69), this would have been a valid question.


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