Tuesday, August 4, 2009

G9 Fill Flash

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Continuing with the G9 flash fixation, this post is about fill flash. Although previous posts are labeled as flash and exposure compensation, fill flash is, in a way, much the same sort of thing.

First, I set up a very contrasty scene featuring the lovely Hannah . A similar situation – although perhaps not as drastic – occurs when an expanse of sky is included in a scene. The G9 was simply placed in Program Mode (P), ISO 80, widest angle, small Flexizone auto focus and evaluative metering. (For uniform comparisons, all pictures herein are the in-camera JPEG.) Poor Hannah! Although she enjoyed the shade and was not squinting at all, the bright concrete driveway convinced the G9 metering system to use 1/1000 sec and f4 to avoid overexposing the scene. What to do?

Fill flash is the answer here. The question is “How much fill flash?”. Rather than deal with theory, classic ratios, etc., I simply turned on the flash and took another shot. Not too bad! On close examination, several interesting changes took place inside the mind of the G9 (remember it was still in Program Mode, etc. but the flash was turned on). First, the exposure settings were changed to 1/500 second at f5.6; those who follow such details (and all aspiring photographers should) will recognize that these settings produce exactly the same exposure as 1/1000 second at f4. This change was made because the G9 limits its little built-in flash to 1/500 second and at 1/500 second the proper aperture was f5.6. Next, the G9 flash pre-flashes to check the effect and then fires at what it thinks is the necessary power. On second thought, Hannah is actually a bit underexposed. More power is needed.

It turns out that the flash picture was taken with the Slow Sync setting turned OFF so I changed to Slow Sync ON. Duh! Same exposure settings and same result. Next I changed to Aperture Priority (Av) mode and set the aperture at f5.6 to avoid confusing myself. Same results. How about Shutter Priority (Tv) at 1/500 second? Same. Not to be denied my right to force my preferences on the G9, I changed to Manual exposure and kept 1/500 second and f5.6 but forced full power to the flash. (Remember that manual exposure mode also means manual flash adjustments.) Same results – that’s when I realized that the little built-in flash was maxed out. With the flash already firing at full power, there would be no point to increasing the flash compensation setting. So ISO 80, f5.6 and a camera to subject distance of about ten feet is about the limit for the G9. (This would be a Guide Number of 56 but I suspect the GN is really about 40.) Time for a bigger gun.

Next, a Canon 420EX was placed directly on the G9. Again, the G9 was put into P mode. The result was definitely an improvement over the built-in flash. Again, several interesting changes were made by the G9 (not by me). The shutter speed was changed to 1/250 second because that is the limit of external flash unless the external flash can handle “High Speed Sync”. At 1/250 second, the correct aperture setting (considering that bright background) is f8. Actually, the G9 did not particularly like either the 1/250 or the f8 and indicated so by showing both in red on the display. Another point of interest is that the color balance was changed when using the 420EX. The G9 was set for automatic white balance so this was an internal decision by the G9.

The Canon 420EX accomplishes High Speed Sync on the G9 by pulsing rapidly. Unfortunately, this means that flash power is reduced for each pulse. Does the 420EX have enough power at High Speed Sync? I switched the 420EX to HSS and fired away. The G9 responded by changing to 1/1000 second at f4 and the 420EX pulsed away (not noticeable to me). As shown here, the 420EX really does not have quite the necessary power but is close. Also, f4 nicely blurred the background as compared to f8.

Last, I replaced the 420EX with a Nikon SB-28. The SB-28 fires from the G9 but the flash power must be set manually and on the flash. The advantage to using the “incompatible” SB-28 on the G9 is that the G9 ignorantly operates at shutter speeds up to 1/2500 second! Realizing that the “correct” ambient exposure was 1/500 at f5.6, I intentionally set the G9 at 1/1000 second and f5.6 to make the background slightly underexposed. The best setting for the SB-28 was at half power which produced this shot. It’s OK, although the color balance is a bit cool.

Conclusions? Well, fill flash can be very useful and is essentially for some situations. The G9 flash is a bit weak but is certainly convenient. The limits on flash power, sync speed and aperture can lead to false conclusions so be aware of those limits. I much prefer external flash (in fact, off-camera flash). The most understandable setup for me is the G9 in manual mode with the SB-28 also in manual mode; however, this setup often requires a bit of tinkering and trial shots – but I’ll get better at it with practice!
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2 comments:

Bronislaus Janulis said...

Gordon,

I'm doing the same, also using the G9 flash with a homemade diffuser to fire my Nikon SB80, all in manual. The G9 flash is dialed all the way down, the SB80 depends, but it's all pretty quick, though like Hannah, my models are pretty inert.

Миша said...

Great post. I use slow sync flash in manual mode with the G9 all the time. One of the things that does bother me is the fact that you only have three settings for flash strengh: full, mid and low. Obviously, more often than not, my ideal flash strength lies in between two of those.