Inconsistent flash exposure with 600EX-RT

[Rkeroack]

I am using an R7 camera and 600EX-RT flashes at a few indoor occasions. Exposure is very inconsistent, where one shot will be perfect, then a few minutes later, shots will look like the flash had little to no effect, even though it went off.  This happens with the camera in program, or apeture priority, or manual exposure.  I there some option in the camera menu I am not aware of?  The flashes work just fine on my 7DII.

Thanks!

[p4pictures]

Since you mentioned inconsistent exposure, and pictures looking like the flash hadn't fired I have a couple of questions about your camera settings and lens.

• What ISO are you using, is it AUTO ISO?
• In the camera Flash control menu, what do you have selected for the Slow synchro setting?
• What setting do you have for Flash control > E-TTL II balance?
• Are you using Canon EF/EF-S lenses on the adapter, third party lenses on the adapter or RF/RF-S lenses ?

The operation of the EOS R7 with flash is different to the EOS 7D Mark II in several ways.

EOS 7D Mark II will only use 1/60th to 1/250th shutter speed with flash and program mode. With aperture priority the camera would use any shutter speed from the sync speed to 30s depending on the ambient light level, unless you have Flash control > Flash sync. speed in Av set to something other than AUTO. If you use AUTO ISO the ISO will vary between ISO 100 and ISO 1600.

EOS R7 will use a shutter speed of 1/60th to 1/250th in both Av and P modes by default. With RF or RF-S lenses ISO AUTO can vary from ISO 100 to ISO 6400, but with adapted EF / EF-S lenses this is limited to ISO 100 to ISO 1600. 

[Rkeroack]

ISO I believe was 800, no Auto ISO.  Lens was a RF70-200 2.8 or a EF 24-70 w/adaptor.  I do not have the camera with me, but I believe the flash setting in the camera is the default setting, flash controll is ETTL.  It was set as a master, as I had a flash behind the subject for some separation from the black background. That flash was set to a full stop less exposure, and did not seem to be the issue, as the photos where the subject moved a bit and you could see the flash head had the same inconsistencies as when you could not see the flash head in the photo.  Maybe I just needed to be at a lower ISO to force the flash to over power the ceiling lights??

[p4pictures]

You mentioned that you were using the on-camera flash as a master, and also had an off-camera Speedlite working as the slave for some subject separation, and that this background unit was set to -1 stop compared to the master unit. The mirrorless cameras use the whole image sensor area for flash metering, and this means that it can be more readily influenced by a background separation light than a DSLR like your old EOS 7D Mark II which had fewer segments for the flash metering sensor and less precision. 

Sorry to be asking a lot, but my experience is that when you have a light aimed back towards the camera it is best to set it for manual exposure since when it's on E-TTL it can have a dramatic effect on flash exposure consistency and accuracy. 

The on-camera Speedlite, is it set to E-TTL or Group (Gr) mode?

E-TTL

If it's E-TTL then how many groups are you separately controlling with the ratio function, A only, A:B or (A:B):C. Is the separation flash in group A, B, or C? How do you control it to have -1 stop less exposure than the on-camera master flash?

Gr - group mode

If your master Speedlite is set to Group mode, then what group is the slave unit set to? If it is in group B, C, D, or E do you have the relevant group also set to E-TTL but -1 exposure compensation?

In my own experience of doing something similar with Speedlites at an event, I used group mode, and set the background separation light as group B. I then set group B to manual exposure with a power level that would give me the desired background separation. Then I used Group set to E-TTL for the main Speedlite on the camera. 

Secondly in low light, I typically use manual exposure on the camera itself. This is because the available light level is usually quite consistent. I often set my camera, shutter speed, aperture and ISO, so that without flash the result is about 1 or 2 stops underexposed. 

Here's how I would expect my Speedlite 600EX-RT to look with this kind of setup. The unit on the right is the background separation light in group B.

[Rkeroack]

Yes, I knew about the group settings; master on camera was A, slave was B.  I did have the slave on ETTL as well, so I'll have to try that as well as all manual on the camera.  I had tried Program and Aperture priority, but by the time the poor shots were showing up, the event was on and I could not make a big change in settings on the fly.  I'll try this out at the house and make sure I have some extra time to experiment before the next one of these.  As an aside, I was able to rescue everthing in post to keep everyone happy.

Thanks for the assistance!

[deebatman316]

Do you have any example pictures to show us. @p4pictures is a flash expert when it comes to E-TTL. I am also well versed in E-TTL flash metering. So something is definitely off. I’ve found EOS R series cameras have better flash metering than any DSLR ever had. I’m finding that this is even true with older EX series speedlites I use. If you have a lot of light getting to the camera. The camera will adjust the flash power when E-TTL is being used. I’ve found Mirrorless to be more sensitive to flash than a DSLR. This is because the entire image sensor is the metering system. Unlike in a DSLR where an exposure chip in the pentaprisim does the metering. Also the on camera speedlite (Sender) is always in Group A. This cannot be changed since this speedlite has to tell the other off camera (Reciever) speedlite(s) to fire. So where is the off camera flash facing. Then is the on camera Speedlite set to fire as part of the exposure or not. What wireless system are you using Optical or Radio. How many off camera flashes are you using. Are you just using 3 or are you using more. Is flash ratio being if so is it set to ABC. Or are all of them firing at the same output.