Comparing full power output using the same modifier
Note: edited June 17, 2016 to add H600 comparison.
Note: edited June 21, 2016 to add more comprehensive H600 comparison.
Often photographers ask about the relative output from various flash units. Especially comparing speedlites with more powerful strobes. The challenge is how to best compare the lights. Each has a unique flash tube position. Some come with reflectors intended for a normal field of coverage.
It seems to me a useful approach is to find a modifier that will accommodate each of the lights, and deliver the light to a subject in a similar fashion. Of all the modifiers I’ve collected it seems the best is an umbrella framed softbox that positions the light source for indirect illumination of the subject.
Bouncing the light back into the softbox eliminates a hot center area of the diffusion panel and means that the speedlite, with its builtin zoomable reflector will also have its output directed across the diffusion panel. The 24×24 box I selected was chosen because its big enough to disperse the output from all three sources across the front diffusion panel. While being small enough to minimize disparity between the light source output and need to “fill the softbox”. I’ve included a picture of the box with a Cheetahstand S bracket and 685TTs speedlite mounted.
The three lights I used for the comparison are the Godox TT685s, Godox AD360, Godox AD600. All three lights were mounted on the same light stand to ensure the modifier front diffusion panel was the same distance from Manny’s nose for all three shots.
I mounted the softbox directly on the AD600 remote head using its umbrella mount. The AD360 and TT685s were mounted in a Cheetahstand S bracket with the modifier mounted via the bracket’s umbrella mount. the front diffusion panel was 51″ from Manny’s nose. All three lights were fired via a Godox X1Ts trigger/controller and set to full power in M mode.
I placed the A7RII on a tripod, mounted a 90mm F2.8 Macro G lens used zone focusing. I set and left the shutter at 1/200 to eliminate ambient light influence.
The exposure setting and the Lightroom Exposure adjustments to get the same reading on Manny’s cheek nearest the light (camera left) and the white square to read the same. The readings, 83% and 89% are what I use as normal exposure readings. The Color Checker ideally reads 93% in the white square. The 4% difference is reasonable given its distance from the light relative to Manny’s cheek. The black square read 16% which is a bit high which is reasonable given its closeness to the light source compared to the white square.
The AD600 reading was used as the baseline. The AD360 and TT685s exposures were adjusted in Lightroom to result in the same reading at the two reference points. The AD360 exposure was decreased 1/3 EV to F12. This is what one would expect given the nominal Ws ratings of the lights. The TT685s was increased 1/3EV from F4 to F 3.5. That means the speedlite has 3.66 EV less light output in the modifier than the AD360. That calculates to about 30Ws from 360 nominal Ws for the AD360.
The white balance was not changed for the three images. The AD600 is 5,500K / +8 Temp and Tint. The AD360 is 5,500K / +8 Temp and Tint. The TT685s is 5,400K / +9 Temp and Tint.
Based on this comparison, the modifier will work with any of the lights. And any of the lights will get the job done with this modifier at a reasonable distance for a headshot. Naturally, the more powerful lights can be powered down. And, if required the speedlite can be helped along with an ISO boost if a smaller aperture is required. As for relative power. Its about what I expected.
The comparison also demonstrates that choosing between the AD360 and AD600 is probably more about features than about maximum light output. Although the extra 2/3 EV can be useful.
H600 comparison to AD600 as monolight
How much light output —power— is lost with the H600 remote head? This question has appeared several times in various photography fora. I have H600 heads for all my AD600 lights. I use them 99% of the time as pack/head units. When the question was asked I took an Ohm meter and measured the resistance of the cable from plug-to-plug. The reading was .5Ω. That is negligible and doesn’t effectively create any voltage drop between the capacitor and the tube.
After doing the power comparison test I described above I realized excluding a test of the H600 head compared to the AD600 monolight made the power comparison incomplete. I did the test this morning. As one would expect, given the ohm meter reading. There is no output difference between the H600 and the AD600 monolight.
For both test shots I had the light set to full power. I mounted the light/head on a stand that was about 4 feet camera right. I attached a standard 7″ reflector and aimed it up to the joint of the wall and ceiling. This created a bounce light to light Manny. I used this configuration to remove any variables other than the H600 from the test setup. I read the output at Manny’s nose, twice for each test. Each reading was F8.0+.4, I set the camera to ISO 100, 1/200, F9.0 and made two exposures in each configuration.
The white square on the color checker read 94.7 to 95.2, depending on where the curser was located, for all 4 exposures. Below are the two test images. H600, then AD600. (Since the wall and ceiling are an off white, I did use the WB clicker to neutralize the white square.) Other than that nothing was none in Lightroom save the crop.
A more comprehensive H600 comparison to AD600 as monolight
While driving the other day I got thinking about how I could do a directly comparative evaluation of the H600 power output to the AD600 as a monolight. I decided the best approach was to set up two lights, one, on the left in the BTS image, with an H600 head. The other, on the right in the BTS image, in monolight configuration.
I measured the distance between the stand holding Manny and each of the light stands. I also measured the height of the 7″ reflectors from the floor to make sure they were the same. Each light stand is equally positioned about 3 inches behind Manny’s stand so the lights could be aimed slightly forward to ensure a shadow down the middle of Manny’s face. Both lights were placed in M mode and full power via an X1Ts on an A7RII with a 24-70 F2.8 GM lens mounted. ISO 100 and 1/250 shutter speed to eliminate ambient light influence.
The meter reading for each light was F22 +.6 to .8 over a three reading average for each light. The readings were taken with the meter dome aimed to the light. The monolight configuration had the higher reading suggesting that it was putting out about .1 to .2 EV more than the H600 head.
I made a series of exposures starting at F22 the smallest aperture on the lens. I then opened the aperture 1 F stop and decreased the power on each light 1EV until I got to F2.8 on the lens. This was to see if there might be some variation as the power setting changed.
The net, when evaluating the test images in Lightroom is that there is no appreciable exposure difference in the two sides of Manny’s face. Its possible to find areas on one side of the faces where the same area on the other side reads .3 to .5 EV more or less. The readings are not consistently brighter on one side or the other. I decided that the ear lobe and side of the nose was probably as close to an ideal place to make comparative readings. The were the same on both sides. Moving the curser around caused an expected range of readings, all within .3% with the same variation on either side.
Here is a gallery with all the test images if you want to look through them.