Mastering your Canon camera - Canon flash gear
October 20, 2013
Guide Numbers
A little known fact is that if you divide the model number of a
Canon speedlite by 10 that gives you the metric guide number.
Most people these days have never heard of guide numbers,
but once upon a time this was how you figured out flash exposures.
You divide the guide number of the flash (or bulb) by the distance
to the subject (in meters if you have a metric guide number),
and that would give you the f-number to set the lens aperture
for a proper exposure.
These days guide numbers are rarely used to determine exposures
(though they certainly could be).
Instead they serve as a measure of maximum light output
when comparing different flash units.
Note that to get a stop more light, you need to multiply
the guide number by 1.4 (actually 1.414). A flash with a guide
number of 60 provides twice as much light as one with a guide number of 43.
The guide number of the 20D on-camera flash is about 13.
When you consider the stop by stop series 60, 43, 30, 22, 16 ---
this tells you that the 580EX flash provides somewhat more than
4 stops more light than this on camera flash.
Canon 600EX
This is the hot new item, with built in radio control. Price is $500.
To use the radio feature you need another 600EX or the new ST-E3-RT.
The ST-E3 costs $300, more than half the price of another 600EX, so
it is not entirely out of the question to consider another 600EX instead.
No Canon bodies have a built in radio wireless master.
Canon 580EX
If you don't want the radio control, this is a fine unit to consider.
With people rushing to upgrade to the new 600EX, there may be good deals
to be had on these nowadays.
Canon 550EX
These are great lights and can often be found for a bargain price.
The only liability I have found is the lack of a PC connector to allow
use with a pocket wizard. This can easily be fixed by someone with
simple electronics technician skills.
Canon 430EX
A great little light, its only liability is that it cannot serve as
a commander for the (somewhat lame) Canon infrared wireless system.
On camera flash as wireless master
The 7D first provided this feature, and now the 60D and 70D do also.
None of the 5D or 1D bodies do of course, since they have no built in flash.
The on-camera flash can act as a commander for the Canon infrared wireless system.
This is a unique and commendable feature.
ST-E2
This is the commander moduler for the Canon infrared wireless system.
I have one, and use it very little. The infrared wireless is less than
robust and I use radio triggers instead. It uses a unique and hard to
find battery. I have head that some people leave it on the camera because
it emits an excellent focus assist for shooting in bad light.
It is expensive enough that another 580EX might be a better choice.
ST-E3-RT
This is the new commander module that does radio E-TTL. Price is $300
It replaces the old ST-E2 infrared unit, as long as you have the new
600EX flash units. It uses a pair of AA batteries, which is nice.
It does not emit a focus assist beam like the old ST-E2 did.
Pocket Wizard Plus X
If you don't want to buy into Canons E-TTL radio system, you can consider
these. A pair will cost $200 - but they are manual only, no E-TTL.
Pocket Wizard Plus III
These are somewhat of an upgrade from the Plus X. A pair costs $300.
You get separate control of ABCD designated units and a battery status
display.
Pocket Wizard Flex TT5-Canon
These offer wireless TTL flash. A pair costs $460.
I have avoided these because there is a problem with radio signal interference
when used with the 580EX and 430EX speedlights.
There was a fix that involved using a shielding "sock" (and additional $35 each).
The last thing I want is something expensive, unreliable, and inconvenient.
I decided to avoid the whole situation and purchased Plus III units.
This may have been a wise decision. The word is that more recent cameras
(first the 5D Mark III, then the 1Dx) broke compatibility with the Pocket Wizard
TTL -- which Canon never issued a public specification for anyway, it was
reverse engineered by Pocket Wizard. Pocket wizard sorted this out and issued
new firmware for these cameras, but people were high and dry for a while.
Other TTL radio devices
There are Radio Poppers, Pixel Kings, Odins, and many others. Many of these are well
thought of (and have proven to be more reliable that the Pocket Wizard TTL devices).
Feedback? Questions?
Drop me a line!
Tom's Digital Photography Info / tom@mmto.org