RGTX wrote:
I have a Canon 6D and I want to get a flash mostly for fill light in daytime. I'm not really interested in a flash that's smarter than I am. I just want a flash that I can attach either on camera or with a long cord that I can adjust the settings to my liking. What do you recommend? Thanks.
Canon 420EX, 430EX, 470EX, 550EX, 580EX, 600EX Speedlites are all very versatile and easy to use. There are also smaller, less powerful 300-series and 200-series, though they may have more limited functionality (likely will be more "automated").
You can use the 400/500/600-series Speedlites either very automated or fully manual or something in between, as you see fit.
Set the flash to "ETTL" and your camera to any of its auto exposure modes, the flash automatically acts as "fill". The camera sets exposure using ambient light metering, while the flash is fired at -1.66 stops of power, to act as fill.... ideal for shooting in strong daylight when shadows can be a problem. You're free to dial the strength of the flash up or down using Flash Exposure Compensation (FEC), which works the same as Exposure Compensation (EC) adjustments to the camera's ambient light auto exposure.
Leave the flash in "ETTL" and set your camera to fully manual exposure and you get "full" flash. Flash will be treated as if it were the sole light source, ambient light conditions ignored by the camera. You still get the effect of auto exposure, but now it's just the flash output that's controlled. You can change the manual camera settings freely... to effect how ambient light is recorded, causing a background to go dark or to lighten up, for example, or for any other reason you wish. You also can still use FEC to tweak the power of the flash to your preferences.
Or, set both the camera and the flash to fully Manual exposure mode, and control it all yourself. It's your choice.
The 400-series Canon flashes are pretty powerful, but a little more compact (Canon flashes' designations are actually based upon each models' Guide Number, in meters... a 420EX has a GN of 42 meters, while a 580EX has a GN of 58 meters, for example... this is pretty much true across all the Canon EX flash line-up).
200-series, 300-series and 400-series flashes all rely upon an internal set of batteries.... aren't designed for an external power source. (Note: There are some third party external power sources that can be used with certain Speedlites, but they require a permanent modification of the flash to do so.) The 200/300/400-serise also mostly can be set to act as off-camera slaves in multi-flash setups, but not as masters.
The larger and more powerful 500-series and 600-series flashes can be set to act either as slaves or as masters in multi-flash setups. They also have means of connecting an external power source for faster recycling and for a lot more shots (Canon themselves offer "compact" battery packs that add eight more AA batteries to the four already in the flash).
The tiny Canon 90EX (now discontinued) also can act as a master, installed on camera and used to fire other off-camera flashes.
Canon also offers the ST-series of on-camera controllers that can be used to control and fire off-camera flashes.
The "RT" flashes and controller use "radio triggering" and control, which has greater reach and less interference than the near-IR optical control used with the other flashes and controllers.
You can use an off-camera shoe cord with most of these. Canon has offered several models of those over the years, and there are cheaper third party "clones".
There are also a lot of third party flashes and accessories that can interact with the Canon Speedlite system... including Yongnuo, Godox and others.
Note: Your 6D has a flash sync speed of 1/180, I believe. That's the fastest shutter speed you can use the flash "normally". However, many of the flashes can be set to do "High Speed Sync" (HSS), which allows faster shutter speeds to be used. This shortens the duration of the flash, though.... and this in turn reduces the distance the flash can reach. The faster the shutter speed, the less reach that will be possible.
A neat feature of the "big" Speedlites (500-series, 600-series) is an LCD display on the back that, among other things, displays the distance range where the flash will be effective, given the current flash and camera settings. This display will adjust as you change lens aperture or ISO.... or when HSS is used with shutter speeds faster than the camera's sync speed. If your lens has a distance scale, that and the flash's display make it easy to check if the subject is withing the working range, even if you aren't good estimating distances yourself.
There are other things the flashes can do..... Such as 2nd Curtain Sync (usually used with slower shutter speeds), stroboscopic mutli-flash effects and more.
Personally I have three 580EXII and three older 550EX, as well as an ST-E2 Controller and a set of five Norman studio strobes. I'm about to buy a 90EX or 200-series for use with a small Canon mirrorless system. (I know your 6D doesn't have one, but FYI built-in flashes that some cameras have really suck! I don't use them. They're weak and located in the worst possible place for redeye problems and ugly shadow effects. They're also slow recycling and quickly drain the camera's main battery.)
If you consider older, used flashes... FYI, the Canon "A"-series, "T"-series and "EZ"-series either are not at all compatible with modern cameras like yours, or will have very limited capabilities. With other older flashes you have to be concerned about trigger voltages, too. While your camera can probably tolerate as much as 250v, some old flash models had 400v and higher trigger voltages (early Vivitar 283, for example). Those flashes were designed for use with mostly mechanical cameras that had no limits on trigger voltages. But more recent, highly electronic cameras can be damaged by too high voltages.