The gap you are actually fighting
On a bright day the difference between the brightest part of the sky outside and the darkest corner of an interior can run twelve to fifteen stops. A modern full-frame sensor gives you somewhere around thirteen to fourteen stops of usable dynamic range at base ISO, and considerably less once you are at ISO 1600 in a basement. So the gap is sometimes bridgeable in a single frame and sometimes not, and the first decision on any interior is which situation you are in. Meter the sky through the window, then meter the darkest surface you need detail in, and count the stops. Five or six stops of spread is a single exposure. Ten is not, and pretending otherwise produces a frame with gray shadows and a magenta sky.
Flash-ambient blend beats bracketing more often than people think
The clean method is to expose for the window and then raise the interior to meet it. Set the exposure so the view outside is correct — often two to three stops below what the room wants — and then bounce a flash off the ceiling or a side wall to lift the interior. One speedlight at half power into a white ceiling will typically raise a medium room by two stops. Two lights placed out of frame will do a large one. The result holds together because everything in the frame was recorded in one exposure, so nothing ghosts and nothing halos. It fails when the ceilings are dark, when they are twenty feet up, or when the walls are a strong color that will contaminate the bounce — in a red-painted dining room, bounce flash turns everyone’s plaster pink.
When you do bracket, bracket properly
Camera on a tripod, manual focus locked, aperture fixed, and change only the shutter speed. Three frames at two stops apart covers most rooms; five at two stops covers the hard ones. Never let the aperture float, because depth of field changing between frames produces soft edges in the blend that look like a processing error. Blend by hand with a luminosity mask rather than running an automatic tone-mapping preset — the preset is what produces that gray, over-detailed look that makes an interior appear to be lit from inside the walls. The goal is a frame that looks like the room looked, with a view you can actually see, not a frame that announces it was made from five frames.
Sometimes the answer is to come back
The cheapest fix for a fifteen-stop scene is to stop shooting at noon. Twenty minutes after sunset, with the interior lights on, the exterior brightness drops to within two or three stops of the interior and the whole problem evaporates. The windows read as deep blue rather than white, the room glows, and you need one exposure. For north-facing rooms, mid-morning overcast does much the same thing. On construction work this is easier to arrange than on a listing, because the job runs for weeks and nobody needs the photograph today — a point worth making to a client who has asked for a shoot on the one afternoon the site is free.
Composition choices that reduce the problem
Stand so the windows are at the edge of the frame instead of the center, and the eye forgives a lot. Shoot from a doorway looking into the room rather than from the window wall looking out. Drop the camera to about fifty inches — chest height for most people — which usually takes a chunk of bright ceiling and bright sky out of the top of the frame. And be careful with very wide lenses here, because a wide lens pulls in more window area and more ceiling at once; the same room at 24mm is a much easier exposure than at 16mm, which is one of several reasons a wide lens is not automatically the right tool for a room.
Frequently asked questions
Can I just drop a sky into the window in post? For a marketing image with disclosure, maybe. For anything documenting a build, no — it is a fabricated element in an evidentiary frame.
How many stops of flash do I need for a typical room? One speedlight at half power bounced off a white eight-foot ceiling lifts a 12×15 room about two stops at ISO 400 and f/8.
Is a mirrorless camera better for this than a DSLR? The live histogram and exposure preview make judging the blend faster, but the sensor range is the same generation either way.