Flash zoom setting while bouncing.

Deni · 10-10-2008, 08:20 AM

I was trying some settings with bouncing the light from the hotshoe flash and it was interesting that using the widest setting for the flash head gave the flash more power than using the flash at the telephoto setting.

I have a Digital Concepts p-ttl flash and it has automatic and manual zoom settings for the head 24-28-35-50-70-85 mm. The difference between 24 and 28 mm was negligible but the narrower setting did decrease the light spread. I used it in a 8.5m x 4.5 m room, almost totally blacked out and f/8 and iso 200 and the flash was set to manual full power.

Unfortunately I don't have the photos with me at work.

rogerstg · 10-11-2008, 03:58 PM

How did you determine that one setting produced more power than the other?

flyer · 10-12-2008, 05:45 AM

I noticed the same thing with my Sigma EF500 DG Super. I think it's not the power at stake here, but more the way the P-TTL processes the information when the wide angle panel is in use. Or, maybe, the wider coverage of the light with the wide angle panel is down makes it easier fo the camera to meter properly. Whatever the reason, I noticed that bounce flash wit the wide panel down is more accurate, so I use it just about all the time.

tomtor · 10-12-2008, 07:44 AM

Originally Posted by Deni

I was trying some settings with bouncing the light from the hotshoe flash and it was interesting that using the widest setting for the flash head gave the flash more power than using the flash at the telephoto setting.

I have a Digital Concepts p-ttl flash and it has automatic and manual zoom settings for the head 24-28-35-50-70-85 mm. The difference between 24 and 28 mm was negligible but the narrower setting did decrease the light spread. I used it in a 8.5m x 4.5 m room, almost totally blacked out and f/8 and iso 200 and the flash was set to manual full power.

Unfortunately I don't have the photos with me at work.

This is not an easy question to answer. A flash tele setting in bounce position projects a small bright rectangle on the ceiling, a wide setting a less bright but bigger rectangle.

The reflected light of the bigger rectangle illuminates the subject more evenly (like a big ceiling window). The tele small rectangle has more the effect of a lamp hanging from the ceiling. Depending on the direction of the flash head and the distance of the subject, it might bounce less light on the front of the subject.

The whole idea of a bounce flash is to simulate light from a big light source like the sky, so using a wide flash setting when bouncing makes more sense. When you use the tele setting, you could/should swivel the head to a dedicated position to get more directed light, eg from a side wall.

Another explanation is that the tele position DOES lose some light, because the flash tube is than located to the back of the unit. The light bounces its way to the front of the flash unit and looses some energy. In non bounce mode this effect is no problem, because now less light is lost in the non visible areas outside the framed area, so you still get more light on the subject. When bouncing all light is effectively used (reflected from the ceiling), so the tele flash position might result in less light than the wide position.