External Flash triggered by camera's internal trigger

Question

I am stuck. I am starting to understand and try Flash photography with my Canon 750D.

I have ordered a yongnuo 560 iv just yesterday.

Now as I am tight on the budget, I have not ordered a trigger for the flash that goes on top of the camera.

My question is, can my camera trigger this external flash?

Does the popup flash in my camera always has to stay up to trigger the external flash?

How to do all this if it is possible?

If this is possible, will there be any difference using a build in trigger vs an external one?

I will be using a soft dome or a reflecting umbrella sometimes so will they be in line of sight using the internal trigger?

Answer 1

The only way to use a 750D to trigger an off-camera YN-560 IV without adding any other hardware is to use the pop-up flash to trigger the YN-560 IV in "dumb" slave mode.

The YN-560 IV has a built in radio receiver compatible with the YN560/RF605/RF603 communication protocol. Your camera has no built-in radio transmitter (none of Canon's current cameras do), much less one compatible with YN560/RF/605/RF603.

Your camera's built-in pop-up flash can communicate wirelessly with off-camera flashes that are capable of receiving optical wireless signals using the Canon optical TTL protocol. The YN-560 IV has no such 'TTL' receiver, optical or radio.

The YN-560 IV does have the ability to "fire" when it detects a bright flash of light. 'S1' mode is the basic optical slave that fires as soon as it senses another flash. 'S2' mode is the optical slave mode that (hopefully) ignores the TTL pre-flash and fires on the second main flash. Both of these modes will require your camera's pop-up flash to fire while the camera's shutter is open. Use straight 'manual flash' for the camera's pop-up flash for S1 mode. If you want to use the pop-up flash in TTL mode, you can try S2 mode, but that tends to be more problematic than S1 mode.

If you want to use the pop-up flash to fire a communication signal to an off-camera flash before the shutter opens but not fire a flash while the shutter is open, you should have considered the YN568EX II or similar flash that is optical TTL capable. The YN685 adds a built-in Yongnuo 622 radio receiver that allows full TTL control via a YN622 transmitter but removes the optical TTL receiver. The YN622 protocol is different from the YN560/RF605/RF603 protocol. Some YN622 devices made since 2014 can be set to receive YN560/RF/605/RF603 commands in manual only mode, but YN622 devices can not control YN560/RF605/RF603 devices.

Answer 2

... can my camera trigger this external flash?

Yes, but not as a Canon wireless master. You have to put the YN-560IV into S1/S2 optical slave mode (use the Lightning/Radio button), and use the pop-up flash as a regular flash. You use S1 if the pop-up flash is in M mode; S2 if it's in TTL, so you can skip the metering pre-flash.

Keep in mind the S1/S2 "dumb" optical slaving is completely different from the Canon optical wireless system.

Does the popup flash in my camera always has to stay up to trigger the external flash?

Yes. Something on the camera has to tell the flash when to fire. And that's either going to be the pop-up flash, or a radio transmitter. Without the add-on transmitter, you have to use the pop-up flash, and it has to fire a pulse bright enough for the slave sensor to "see". You can set the power of the pop-up to be minimal, and it should not register in the image at regular (non-macro) subject distances.

If this is possible, will there be any difference using a build in trigger vs an external one?

Yes. If you get a YN-560-TX transmitter, you won't have to wrestle with the line-of-sight issues required by optical slaving. The light sensor on the flash has to be able to "see" your pop-up flash to be remotely triggered, so it's difficult to use a flash behind you, or behind a solid object. The light signal can also be overpowered if you try to use optical slaving outside in bright sunlight.

The YN-560-TX is a radio trigger, so isn't affected by either of these factors. In addition, it can let you remotely set the power and zoom on the flash from the camera.

However. A Godox TT600 and X1T-C combination would cost roughly the same and also give you HSS capability over the remote flash, while giving you far better expansion options in the future.

I will be using a soft dome or a reflecting umbrella sometimes so will they be in line of sight using the internal trigger?

Depends on how you set things up and whether there are bounce surfaces around. The red panel on the front of the flash is where the optical slave sensor is.