Well i you can easily detached your flash and put it to CSM mode.
The steps are as follows:-
1) Go to menu in your camera, under built-in flash, put it in CSM mode channel 3 or watever.
2) Open the built in flash.
3) Switch on external flash and put it to CSM mode. (channel must be same as what u configure in camera)
4) Place external flash near to the people in foreground. (direct and make sure flash is not caught in camera's view)
5) Lover shutter, not too slow and not too fast. Use trial and error to find out. (See whether background can be seen or not. Same goes for your apeture.. Cause tis way easier la for me to explain rather than do the math thing.. not my style.)
6) ISO can be around 400-800.
And you're good to go..!
Here is an example of a photo.
Surrounding Area is dark but background is lighted.
I used what i explained on top as an experiment and it worked.
Thus, im sharing what i found out with all. As im still NEW and yea.. Still learning!
So pardon me if explaination is a little noobish..!
For this shot, my external flash is placed on the tree, facing direct to us.
Taken with a tripod.
Oh ya and make sure your sensor on flash is facing your built in flash for it to
be triggered!
Picture is unedited. Straigth from camera.
Except the resizing. Quite bad picture after resize but
just want to share the lighting part. so yea..
Hope this helps you.
Newbie trying to help..
hehehe
EXIF on shot:
f/4.5
1/6 s Shutter
ISO 800
focal length 52mm on 18-70mm.
EXIF on shot:
f/4.2
1/6 s Shutter
ISO 800
focal length 44mm on 18-70mm.