Sony TTL Metering Characteristics

Note: 6/21/16 Update with additional TTL exposure testing

Recently a post appeared on a photography forum asking about underexposed images with the Godox AD600 TTL monolight.

TTL exposure is somewhat tricky in that its related to the camera exposure, which the algorithms presume to be the correct ambient exposure. The Sony A7RII I use has three flash setting options available via its menu; Fill-Flash; Slow; Rear; and one that isn’t relevant — Wireless.

Considering the concerns expressed in the post, I thought it would be useful to evaluate how the XPLOR600 performs in TTL. Since I have a TT685s speedlite I decided to include it in the test for comparison purposes.

Recently Godox updated the firmware for the TT685 and the X1Ts. I downloaded the updated firmware into my devices when it was available for download from the Godox website. All this testing was accomplished using the latest firmware for the X1Ts, the TT685s and the XPLOR600.

Following the images illustrating my testing, I’ve included some images from a wedding I shot last Saturday. My lighting scheme was one XPLOR600 in each corner of the Medinah Country Club ballroom. The Gr A and C lights were set to 0FEC. The Gr B and D lights were set to -.7FEC. Facing the bride and groom’s table the lights were A, B, C, D. With A camera right and D camera left. I use this scheme to provide main/fill/kicker lighting from any position in the room. The lights were triggered with an X1Ts.

There are two versions of each image; first processed with the Lightroom processing shown in the caption; second unprocessed (UP) for comparison.

The series of images below illustrate what I discovered.

  1. The TT685s delivers essentially the same exposure with TTL metering in M mode with handheld flash metering.
  2. The XPLOR600 is one EV underexposed in TTL metering compared to handheld metering in M mode.
  3. The XPLOR FEC settings are accurate. +1 FEC brings the exposure up to the M mode baseline exposure. .7 and .3 FEC are equal 1/3 EV steps.
  4. The three flash mode options for the camera have no impact on the TTL exposure.

My conclusion is that the XPLOR600 TTL settings are off by 1EV. The same X1Ts was used for the testing with both the speedlite and the XPLOR600.

The first 4 images in the series below show the TT685 and XPLOR600, first in M mode and then the TTL exposure as corrected in Light Room. The amount of exposure compensation is shown in the caption under the image.

The next 5 images show the uncorrected images from the XPLOR600 FEC test. First the M mode exposure then the TTL exposures. The FEC setting is shown in the caption.

Here are the reception images:

For these images, the camera ambient exposure was set to Auto ISO, Av, F4 or there about. Given the Sony A7RII ISO performance I’ve found this approach works well. It also means that backlit situations like the cake cutting and first dance will be influenced by the bright background. Also, later in the evening strong ambient light sources like the wall sconces may influence the exposure. With these sample images, even the image of the bride and her dad dancing, when brought up 2EV does not show any chromatic noise in the shadows. Especially the dad’s suit.

The cake cutting image shows lights A (camera left) and B in the background.

The image of the bride’s mom and dad toasting the couple show lights C (camera left) and D in the background.

6/1/21/16 Update: Garden wedding and more testing

I used the AD600 for the group and family pictures, as well as some with the couple at a garden wedding this past weekend. The EXIF data is with the images in the gallery. Generally, in these situations I us Av and EC and FEC to get the ambient/flash balance I want. This situation worked as expected without any apparent under exposure from the TTL strobe metering. It does seem to confirm that the FEC is related to the nominal metering for the ambient. Which makes sense.

Here are a few images from the wedding. The first one is without any flash contribution to create a visual baseline.

Testing FEC

I had setup Manny and two AD600s, one with an H600 head for a power comparison test and decided to run through some Flash Exposure Compensation scenarios as well. Here is a gallery of the images with EXIF data below.

One thing that I did confirm, based on a forum tread contribution, is that FEC set on the light is additive to FEC set with the X1T. This is a critical element because of the potential to have a light with FEC dialed in on the light without realizing it. When the light is in TTL mode, spinning the wheel around the set button changes FEC. This happens without having to first press a function button on the light. Thus, the potential exists for one to inadvertently change the FEC on a light while setting it up.

The EXIF data for the images in the gallery don’t change because the camera setting remained the same. All that was changed were the FEC settings for the two lights via the X1Ts controller/trigger. The FEC adjustment test was conducted with the light camera right. The additive contribution is apparent by the overexposure in one image. The following images illustrate how changing the FEC with the X1T can then be used to balance the exposure.