Sony RX10iii with Cactus RF 60 flash and V6 trigger.
Maybe it's because I can be a control freak when it comes to lighting but I never really warmed up to TTL automatic flash exposure with flash. I like to set exact power settings because once I lock into a "look" or exposure I like I want the flash to put out exactly the same power, over and over again, until I move on to the next subject. Please don't assume that I don't understand the benefits of automation when it comes to flash, and even off camera flash, after all, I wrote a best selling book on the subject back in 2008 for Amherst Media.
No, I want my light to be consistent from flash to flash and that's something you give up when you allow the camera to control the flash, based on TTL readings. Moving the camera so it sees a different part of the subject, or moving into the path of a reflection, will change the exposure. At best it means you won't be able to easily batch photos; you'll have to fine tune exposures that change. At worst it can mean that your ratio between existing light and flash light is all screwed up, as is the color balance, etc.
So, in this very short blog post I am going to tell you how I typically work with off camera flash and mirrorless cameras like the RX10 series.
First things first. There are no disadvantages to using a mirrorless camera set up with flash. In fact, there is one big advantage. Mirrorless cameras have two settings that allow you to view images before shooting in two different ways. You can see exactly what the camera will eventually give you based on your exposure settings. If the setting make the image too dark you will see a dark frame. If the settings make the image too bright you will see and overexposed frame. You get this effect when you have "setting effects on" in a Sony. That means the camera is overlaying all of your settings when it shows you the frame you are considering snapping. It's a wonderful way to work when not using flash because you have a much better chance of estimating exactly what you future image will look like once you've shot it.
But traditionally an optical finder shows you the same basic scene through the finder no matter what you have set. You could have your shutter speed set for 30 seconds but you won't see overexposure when you look through the finder; just a pleasant image which your eye compensates for, making it look to you like real life. There's really no way, other than experience (or blind trust in the metering) to understand what the image will eventually look like.
Sounds stupid to pass up a good, accurate preview for a pretty image that lies but that's what all the defenders of last century's technology (the optical viewfinder) are doing when they rush to defend the non-preview of OVFs. There is one place where this system works as well as the EVF on a mirrorless camera and that is when using flash. Whether your ambient exposure settings are dark or light the OVF shows you a bright image most of the time. At least bright enough to focus on...
If you leave the mirrorless camera of your choice in the "setting effects on" setting you might get a really dark finder or a really bright finder depending on the conditions created by your exposure settings. The camera shows you what you WILL get and not an image disconnected from the holistic process. It's not an optimal way to shoot flash because you'll need enough brightness on the EVF to compose the subject.
Easy-peasy. If you turn off the "setting effects on" feature you'll get the electronic mimic of the old optical viewfinder. The camera will create a balanced, automatic exposure level that makes your viewing less accurate but more practical for flash.
Just for example. If you are in a dimly lit room, shooting at ISO 100 and want f5.6 as a starting point for your flash exposure and you would like to set a shutter speed of 1/125th of a second to freeze any subject movement, those settings (with "setting effects on") will give you a very, very dark finder... nearly black. Hard to work and hard to compose upon. If you switch the "setting effects off" you get a bright, even and automatically compensating (for overall exposure) view.
Onward. I like to use manual settings with my flashes. So I get a meter reading for the ambient light I'd like to have as part of my exposure mix and set the camera there. Then I experiment with various flash levels (in manual) until I get the balance between ambient and flash that seems correct to me.
If nothing changes I can move the camera all around without changing anything about my principal exposure.
On the Sony RX series cameras (and on my other cameras as well) I use a flash trigger in the hot shoe and a radio trigger controlled flash on a light stand to get the light I want. Right now I am using Cactus V6 radio triggers with Cactus RF60 flashes. They are totally manual and totally reliable. They trigger whether I am in close proximity or across a big space. They also trigger without failure in soft boxes and other modifiers. The Cactus combination allows me to use up to four groups of lights and also allows me to control the flashes, in thirds of a stop, from minimum to maximum power, from the camera position, using two buttons on the shoe mounted flash trigger.
Usually, when I am using off camera flashes I'll be using more than one flash and it's typically when I am doing a location portrait or a small group of people.
With decades of experience I am usually able to guess the approximate exposure but, like everyone else, I take test shots to narrow down the slop and get to exposures that are just right. I could do the same thing with a meter but it's quicker and easier just to chimp it until I hit it.
The advantage in using the RX10 series cameras with flash lies in their ability to sync all the way up beyond 1/1000th of a second with no major trickery or machinery involved. Just set the power and the shutter speed where you want it and, voila, trouble free exterior fill flash at your fingertips.
A lot of the time though I am working with mono lights in the studio or on location. In these situations I use a generic flash trigger from Wein that, when triggered, sends out a pulse of infra-red light which triggers the internal slave eyes on all my flashes. It's a small trigger that also fits in the hot shoe and requires little, if any, technical skill. No channels to set, no groups to corral. Just a pulse of intra-red and the musical sound of big lights quickly recycling.
By doing everything in manual I never get burned by not paying attention to something the cameras are doing without my permission.
Wanna do flash just like we did in 1999? Or 2010? Or 2015? Put a flash or a trigger in the hot shoe of your mirrorless camera, set the manual power level where you think it should be and then test to taste. Just remember to turn your controls to: "setting effect off" for flash.