This is a review of my experience with using flashes with a Canon DSLR. For people new to photography, I highly recommend learning how to use your camera in ambient light first, and avoiding use of flash completely until you are at least comfortable with use of your camera in Aperture Priority mode. Once you are familiar with your camera and have lots of experience in various types of ambient lighting (daylight, night, indoors), it is worth looking into use of remote (off-camera) flash. In a pinch, bounce flash is useful, but don't plan on using that long-term for professional results. Use a reliable off-camera system - a transmitter on your camera fires the flashes which are set up at pre-determined places in the room. My review of the modern Canon system is below...
Canons's greatest invention
Canons's greatest invention
This is not a flash but just as important - a trigger that fits on the hot-shoe of your Canon camera that controls your radio frequency flashes. There is just one thing that could significantly improve this device: make it compatible with non-Canon camers, such as Sony and Nikon. ...Oh, wait, Yong Nuo just copied this device and did exactly that.
The ST-E3-RT. In my experience, this thing, and the Canon radio-frequency flash system, is rock solid! I love this transmitter. I used to have Canon's previous system - the 580EX II and 430EX II. I did not find that old system reliable as far as off-camera flash, especially behind objects/walls. I used a Cactus v4 system, which was supposed to be good. It was not reliable enough. I was needed to shoot a wedding in Belfast, and before going I tested out the Cactus v4 system with the old flashes. It was so unreliable, I left it behind in Canada, and just shot with ambient light.
But the new Canon RT system is totally reliable, at least in the way I use it. I highly recommend the ST-E3-RT and the new Canon flashes, especially the 430EXIII-RT - and I would probably highly recommend the Yong Nuo YN-E3-RT, but I haven't tried that one out. The ST-E3-RT even has weather sealing, and so does the Yong Nuo version!
The downside to the Canon one, as noted above, is that it only works on Canon cameras. The Yong Nuo version supposedly works on other cameras, if you have installed the latest firmware on the Yong Nuo device. In the slideshow below, you can see the seal (or lack of) when attaching one of these to a Nikon camera - the area around the hotshoe is slightly different on a Nikon (compared to a Canon camera) resulting in an incomplete weather seal. The photos below show a D3200 but I also tried it on a D850 and saw a similar incomplete weather seal. Just so you are aware. As mentioned before, I haven't tried the Yong Nuo transmitter yet so I'm not sure if this would cause malfunction if doing remote-flash photography in the rain. For what it's worth, one time I was standing in the rain while installing the Canon transmitter on my camera so the contacts were slightly wet and everything still operated as normal.
A second limitation I can think of, it's that the radio frequency system has a certain range, I was in Bankers Hall and trying to use my flashes way down atrium, and they did not fire. I had to move them closer to me, which was about a third to half way down the atrium.
The third limitation is not with the ST-E3-RT its self, it's with the flashes: currently (in 2018), Canon flashes require time after firing to recover back to full charge. This is to be expected of any battery-powered flash, but be aware, a different flash company - Rotolight, have figured out how to have a flash with almost zero recharge time (I have seen videos of firing even at 10 frames per second so that is essentially zero recharge time - most cameras don't even have a frame rate that high). I haven't tried it, and don't know much about it, but worth looking into...
My favourite flash. This thing is excellent and I prefer the size of this one to the larger flashes like the 600EX-RT.
This flash works very reliably and is smaller in size than the larger 600EX-RT.
Unlike the larger 600EX-RT, this flash does not have weather sealing.
Awesome value! This is an excellent flash, especially for the money.
Context: I use this with the Canon ST-E3-RT transmitter. Although both the transmitter and the flash have ETTL capability, I use it in manual mode since I don't expect camera to know where my flash is in relation to my camera and I don't expect it to know how my light modifier (umbrella or softbox) is going to affect the amount of light reaching the subject. The ETTL function is probably something I need to experiment with more, but for me, manual mode works well.
Less than half the price of the Canon 430EX III-RT, and a small fraction of the price of the Canon 600EX-RT. This is designed to be basically the same flash as the Canon 600 but made by Yongnuo. This Yongnuo has weather sealing, I shot it in the rain.
This flash turns its self off randomly. I usually notice pretty quickly and I have to walk over and turn it back on. On average, I would say this happens to me about 2 to 3 times per photoshoot. For that reason alone, I prefer the Canon 430EX III-RT, and if I'm only taking one flash with me - such as for an outdoor shoot - I will take the Canon 430. The other reason I prefer the 430 is its smaller size. I also find myself changing the batteries a lot more often on this Yongnuo 600 than I do on the Canon 430, probably mainly because the Yongnuo has more power.
A comment about the weather sealing: on some lightstands, the weather sealing would be imperfect unless attaching the little foot and then putting that on the lightstand. You can see the gap on some lightstands/flashmounts in the photo below:
Weather sealing issue on lightstands
Though the flash has weather sealing, there is a gap at the front at the base as it does not line up with the flashmount on some lightstands. However, for me, in the rain this did not cause an issue. Maybe it would if you were out in the rain for long enough. The solution is simple anyway - attach the foot to the lightstand.
Though the Yongnuo YN600EX-RT appears to have some subtile limitations where there is room for improvement, I still recommend it because it is just such good value for the money. You could get 3 or 4 of these for the price of a new Canon 600EX-RT.