GoofyNewfie Loc: Kansas City

TTL= Through The Lens metering.
More here.
Your Olympus has it too.

bertloomis Loc: Fort Worth, Texas

Set your camera flash so that it always fires. Approach the window and fill the frame with the outdoor view. Press and hold the shutter button half way down. This sets the exposure for the outdoors. Keeping the button pressed halfway down, recompose the shot with the people in it. Press the shutter release button all the way down.

The outdoors will be correctly exposed because you metered it by pressing the shutter button half way down and holding it there. The people will be correctly exposed because the camera measures the reflected flash light coming through the lens.

The only time this has failed me is when the outdoors is extremely bright and I am using a point and shoot camera with a weak flash. Under these conditions, using the method I just outlined, the outdoors is still correctly exposed but the people are under exposed.

RaydancePhoto

Most flashes are not capable of syncing faster than 1/250 unless you get one specifically made for higher SS. Usually the sync speed for flash in around 1/250 max. Too slow to be able to control the ambient light and still get enough light on your subject. So the window light usually gets blown out.

I am going to suggest using High Speed Sync (HSS) to override the ambient light from the window. 1st, you will need to use a flash that is capable of HSS, I use Sigma EF-530 DG Super flashes, very powerful and flexible flash units. Discontinued now, but that have newer models.

You will need to use your camera in manual for HSS. Use the shutter speed to override the ambient light from the window, and set aperture to control the light from the flash.

Here would be my starting point for taking that kind of pic. Meter your camera for the window light at say SS 1/250 in Shutter mode. See what the camera wants for the Aperture.

Now go to manual mode, set the Aperture to 1 - 2 stops smaller from what you metered (if you metered at f/8 bump up to f/11 say for starting point), set SS to 1/2000 and take a shot. You may need to adjust your A or SS depending on the desired effect you want to get.

The high SS will control the ambient light and the flash, using HSS, will fill the light on your subject.

I use this method a lot, you can take a pic of a subject in full sun and darken the background to make the pic look like it was taken in moonlight.

GayleSalamone Loc: Tampa Bay area

Thanks for doing the research for me. I am just not that advanced to have a need/desire for off camera lighting.

photoman022 Loc: Manchester CT USA

I would expose for the background and adjust the flash output (you say you're at 1/4 flash--and I assume that's flash power and it's a manual flash) upward to possibly 1/2 power and see the results. If the people are overexpose, I would scale back the flash power. If they are underexposed, I would up the flash to full power.

My starting point for this type of photography (and I mostly shoot off camera flash) is 1/125 @ f/5.6 ISO 200. The camera setting is separate and distinct from the flash setting. I set the flash at 1/2 power and work from there. With practice you'll be able to eyeball the setting and get the right combination within 3 shots.

Jim Peters Loc: Pittsburgh

i Really Like Your Shot. This Is One We Did

camerapapi Loc: Miami, Fl.

TTL means through the lens, in this case through the lens flash. It is a term used since the early 70.s when this modality was introduced. The light from the flash is metered by the in camera meter for the subject without considering ambient light. TTL-BL is another modality by which the flash and camera communicate with each other. It is made to meter ambient light and flash during the exposure while offering compensation to balance flash and ambient light automatically. It could work pretty well for those backlighted subjects where you are having issues.
As I said, when TTL flash is used metering is done for the subject only reason why it is the recommended modality for interiors. If the background light is metered and the light from the flash is cut by 1 stop then we have a perfectly well exposed background and a good amount of flash illuminating the subject to make the flash exposure more natural.
It is a great idea to use off camera flash under these conditions, ideally with a softbox to soften the quality of the light from the flash as the gentleman that posted a beautiful portrait in this thread has suggested.
All this could seem intimidating but it is not and actually it is easy to do once the basic knowledge of flash photography is understood.
Just to give you a hint, when using flash the aperture in use control the flash exposure. Shutter speeds control the amount of ambient light that will be registered on film or sensor.
All manufacturers of flash use TTL.

AdkHiker Loc: Northeast

Try using manual on the camera. Set it to f11 for maximum sharpness. Set a speedlite to manual an f 11 and place it with a diffuser at the recommended distance (preferably off camera) then meter off of the window and adjust your shutter speed until you have the proper exposure... You should end up with a good exposure of your subject and the outside

I am sure Capt C can expand on this

JPL

To get in the right direction with a solution start with your usual settings, then check your aperture setting. If you are using f8, go to f16 instead and increase your flash. If you are using f5.6 go to f11 instead and increase your flash, if you are using f11 go to f22 instead and increase your flash, if you are using f1,8 go to f4 instead and increase your flash and so on for other aperture settings you may have been using. Do not change the ISO or the shutter speed. This should get you a much better result.

What you need basically is smaller aperture and more flash to balance your background and foreground light as someone already said here.

AntonioReyna Loc: Los Angeles, California

You will almost always get that effect. It is the nature of the setup, not optimal but you do what you can. The main thing is to get good image of the person. Sometimes, you purposely do that for a special effect.