I doubt you can use the on-camera flash with in-camera HDR, that’s not something typically done. In fact, the in-camera HDR is sort of put there as an alternative to flash… in a sense. But if you really want to do HDR with flash you can work around it by compiling your HDR images externally, in a computer using third party software such as Photomatix. In my opinion there just isn’t enough flexibility with in-camera HDR – much as the way I’d never have my camera process an image into a jpg when I could have a RAW file that I can adjust however I see fit in post. With in-camera HDR you’re stuck with whatever the camera gives you.
You can expose the images however you see fit, using flash and/or not, and then just process the images externally. You have far more control when it comes to how you blend those into an HDR image. Personally, when I’ve done HDR, I usually end up blending the final HDR composite back into some of the individual files (usually the brighter ones) to get something that looks a lot less manipulated anyway. The images that come directly out of the software just look too processed for my likes.
Secondly, if you have external flashes, you can simply control the flash power levels, and again blend them in another program. You can do this with the internal flash, but it’s a little more contrived.
Interesting. The one area that I still use HDR is actually for interior photography for RE/architectural. I can’t say that I’ve tried the in-camera HDR with my 6D, I just assumed the results wouldn’t be up to the level I want. Perhaps I’ll give it a look.
I have done something similar to what you’re looking for by triggering my flashes with a RF trigger (Yongnuo RF-602) and using full-power pops on my flash(es). At full power the recycle time is longer than it takes to snap off several shots. So, in effect, you get a flash on the first frame but not the next several. It’s not a reliable solution though.
Sure, but you'll need additional triggers. I have Canon IR triggers that work, but it's line of sight and you have to click the button each time (it won't take all 3 shots - although I haven't tried it in the HDR function).
I also have extra Yongnuo RF-602s that I can use to trigger my shutter (on a different channel than my flash triggers). With the Yongnuo triggering my shutter all I have to do is hold it down for a moment and the camera will rattle off shots as fast as it can. If found the Yongnuo triggers very useful when I want to remotely trigger rapid shots.
My triggers have a little three-pronged input jack on the side of them, and they come with a cord that screws into that port and plugs into my camera. Looks like this:
09/26/2023: New firmware updates are available.
08/18/2023: Canon EOS R5 C training series is released.
07/31/2023: New firmware updates are available.
05/31/2023: New firmware updates are available.
05/18/2023: New firmware updates are available.
03/30/2023: New firmware updates are available.