I've been testing the Metz 45CL-4 with the Cactus V6 and here are the details of how I tested the combo, and my findings:
Profiling:
In a dimly lit room, I placed the Metz 45CL-4 analog version with the SCA 3000C cable and 3702 Pentax TTL module (firmware M2) and the Cactus V6 (firmware 1.0.152) on a table. I positioned the front of the reflector of the flash gun, and the V6's optical slave exactly 100cm from a wall painted in a flat white. I followed the instructions that came with the V6 unit, setting the flashgun first to TTL, and checking for compatibility, then taking a measurement at half and quarter power, and in "winder" mode
which is 1/64th power [see my Update #2 for more details]. I choose the option to skip 1/8th, 1/16th, 1/32nd and 1/128th power levels because they are not available in manual mode on the 45CL-4.
A note on guide number (always in meters): During the profile creation process, the Cactus V6 asks the user to input the guide number of the flashgun being profiled. Most modern flashes have a zoom head with a Fresnel lens on the front to concentrate the light as needed for different focal lengths. The Metz 45 CL-4 does not have a zoom head, it is always set to a 35mm focal length.
Here's the thing to understand though: even though the quoted guide number of the 45CL-4 (45, in meters) may be lower than most top-of-the-line flashes these days, it actually emits more Joules of energy, albeit over a wider angle. Putting a flash head in a softbox
negates the advantage of the zoom head, it levels the playing field as it were. So if one were to zoom the Metz 58, for instance, out to the 35mm position to match the 45CL-4's angle of coverage, the GN would be 35. So, by doing a little algebra... in a softbox, the 45CL-4 would actually provide as much light as a
zoomable flash with a
GN of 75!! That's a lot of power, and one of the main reasons to own this flashgun. Since I will most often be using the 45 in a softbox, I choose to input the GN as 75 ...or rather I would have, except the V6 only allows the user to input guide numbers up to 70, so I did that instead. The only time this really come into play is when using "absolute" power mode on the V6 in order to calculate the contribution of flashes with different max GNs. I can deal with a little discrepancy.
Testing:
I positioned my newly profiled 45CL-4 and the Cactus V6 on a light stand, then placed another light stand 300cm (3m) away to give an approximation of an average working distance, and to it I attached my Sekonic 758 DR light meter using the factory default calibration with the dome in the down position, pointing directly at the flash head. The flash head was "bare bulb" with no wide angle spreader attached. Using a second V6 as the controller, I took readings at each full stop. Ideally there would be a corresponding change of 1 stop for every power level on the V6's dial. Here are the results from the Sekonic meter.
- Full - f/11 and 1/10th
- Half - f/8 and 4/10ths
- Quarter - f/5.6 and 4/10ths
- 1/8th - f/4 and 5/10ths
- 1/16th - f/2.8 and 4/10ths
- 1/32nd - f/2.8 and 3/10ths
- 1/64th - f/2 and 8/10ths
- 1/128th f/2 and 4/10ths
- "Lo" Power - f/2 and 3/10ths
Not exactly as accurate as it could be, still it a big improvement over only having 4 manual power levels, with a notably large gap between 1/4th and
1/64th 1/40th power.
Without changing the setup I then tried using the factory profile that came with the V6 for the Metz 58AF-2 (still using the 45CL-4 in the test though), and here are the results:
- Full - f/11 and 1/10th
- Half - f/8 and 5/10ths
- Quarter - f/5.6 and 4/10ths
- 1/8th - f/4 and 5/10ths
- 1/16th - f/2.8 and 6/10ths
- 1/32nd - f/2 and 9/10ths
- 1/64th - f/2 and 0/10ths
- 1/128th - f/1.4 and 5/10ths
- "Lo" Power - f/1.4 and 1/10th
Here the results were better, still not the ideal 1:1 relationship of input to output, but at least it managed to break 6 stops of variability, with a more predictable shape to the curve.
Conclusions:
The V6 is compatible with the Metz 45CL-4 with some limitations. The factory profile for the Metz 58AF-2 though provides finer controls over then unit than the custom profile generated by the V6.
Why is that? Well, it is likely because of the large gap between one-quarter and
1/64th 1/40th power levels on the 45CL-4. The Cactus must interpolate the proper quench timings in milliseconds for the intermediate power levels based on only a few data points. It may also be that 1 millisecond may not be a fine enough scale to resolve all the 10ths-of-a-stop between power levels (i.e. the sum of the parts may be greater than the sum of the whole... stop)
Perhaps Cactus will some day provide us a software based profile creator to allow users to tweak the quench timings based on their own measurements with their particular equipment.
Thoughts:
One might choose to see the V6/Metz 45 combo for it's faults - uneven scaling, six rather than eight stops of variability, and difficult-to-quantify GN - as a less than ideal system. Fans of the 45CL-4 however know just how much power the little potato masher brings to a location shoot, especially when fitted with a softbox or umbrella vs. a shoe mounted flashgun. The V6 adds much finer controls to the unit than were ever available through Manual, Auto or TTL, making it a welcome companion to the 45CL-4, and breathing new life into a trusted old workhorse.
I am very happy with the V6s, and I can't wait to try them and my new RF60s on a location shoot. I don't see them replacing my studio strobes, but I can conceive of situations in the studio where the ability to change power levels quickly and turn on and off groups of lights might trump the need for raw lighting horsepower.