Understanding Flash Power Output - Canon/Nikon, Quantum and Metz Guide Numbers

Started Feb 2, 2014 | Discussions thread
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MichaelVadon Senior Member • Posts: 1,225
Understanding Flash Power Output - Canon/Nikon, Quantum and Metz Guide Numbers

Its taken me a time to understand the different flash systems guide numbers and output.

First, its important to acknowledge that each flash system has its own "IQ" which takes a while to understand. The OEM flash units from my experience has the best "IQ". You can easily snap on an OEM unit and get decent photos ieven if you have never used them before. Thats just not the case with either Quantum or Metz. You need to read the manuals, experiment and learn how to use the non-OEM units. There are certain intricacies with each of the non-OEM units and you really need to learn them to get the most out of them. That learning comes through time, experience and research. There are some people who may never learn the non-OEM units because they simply dont have the intelligence or time to learn them.

There are also different mechanics associated with each of the units. Quantum flashes are very durable. I have dropped the Quantum Trio and there was not a scratch on the unit. I once put the T5D-R through a torture test of 100 full power flashes. Eventually, the battery pack overheated and shut down for a while, but the actual flash unit did not. I think it was around the 70th full power flash the battery pack overheated and shut down. On the other hand, the Metz and Canons do overheat. The Canon manual states you should wait 10-15 minutes after 20 consecutive flashes (no mention of full power flashes). The Metz manual, as well, states you should give it a rest after 20 consecutive flashes. My personal experience with the Canon 580 EX II suggests during an event was a temporary shutdown.

Another dynamic is the color of the light. The Quantum color is more towards daylight around 5800k while the Canon is somewhere north of 6000k. The Quantum reflector creates a different spread of light versus the other flash heads.

When discussing guide numbers, the numbers change depending on many factors such as using a difuser or a different reflector. Another factor is the guide number says nothing about the spread or quality of the light. The guide number is just a measure of power.

The Canon/Nikon and Metz units have a variable guide number. Depending on the focal length used there is a different guide number. The Metz literature states the Metz 76 unit has a guide number of 54 at 35mm and 76 at 105mm. The Canons most ideal guide number is 60 with the flash head zoomed to 200mm, but the guide number changes to 26 at 20mm. Keep in mind that when you have zoomed the flash head to create a higher guide number the actual light beam coming out of the head becomes narrow. So you cant photograph a large group of people with the flash-head zoomed to 200mm.


Using the Quantum's standard reflector the guide number is 50 for the T5D-R and 70 for the X5D-R regardless of the focal length. Therefore, the Canon unit has a higher guide number when the flash-head is zoomed. The Metz unit seems to be a slightly more powerful flash then the T5D-R. The Quantum Trio unit is about half as powerful as the T5D-R. It really isnt meant to be used as a single unit. The Trio is supposed to be used in combination with a T5D-R on a lightstand and the Trio is meant to be fill light.

Here are my conclusions:

The Metz 76 is really a powerful unit outclassing the T5D-R and the Canon/Nikon units. I would say the Metz is probably the "King of Bounce". I know the Metz 76 combined with a Quantum power pack is used as standard aboard many cruise lines. Many wedding photographers depend upon the Metz 76. However, the Metz doesnt have the radio controls of either the Quantum or the Canon units. It doesnt have the same spread or light quality of the Quantum unit. The Metz 76 is probably the best choice if you just plan on using a single on-board unit. There are ways to integrate an off-camera flash along with the Metz, but its not as seamless as the Canon or Quantum units. The manual does state not to fire the flash over 20 times consecutively and internet forums do suggest there is a point where it will overheat. There is an internal fan so the overheating should not be as much as the Canon/Nikon units.

The Canon unit is the most widely used flash out there. I saw many wedding photographers fielding the Canon/Nikon OEM units this summer. Its very portable, the AA batteries are easy to find unlike the battery packs of the Metz/Quantum units and its compact. You can fit quite a few of the Canons in a bag. The IQ on the OEM units is simply the best and easiest to understand quickly.

The Quantum units have a different quality of light and spread then the others. In the lower focal lengths, there is more power output, but in the higher focal lengths above 100mm its not as powerful. The Freexwire system is the best out there. I had 5 Quantum flashes going all at once at an event this summer and it worked perfectly. I turned up or down the power of the flashes at will using the Quantum Trio remote. The Quantums can be fired off rapidly and they will not shutdown. Keep in mind the battery packs will shut down at the extreme. If you sit there like I did hitting the full power button every few seconds the pack will shut down after about 70-100 shots. However, the flash itself will not break.  It is not easy to understand the Quantums.  Its taken me some time of using them, reading the manual and speaking to customer service.  On some internet forums there are some people who never seem to learn them and revert back to the OEM units.

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