Recently my wife Levi (a Realtor for 26 years) erupted in laughter at her computer and showed me these photos on an email flyer she for a listing in Tacoma, WA. What my wife was laughing about is the row of little photos along the bottom that all have wacky verticals. When you line them up together you get a particularly strange effect. It makes my stomach queasy!
The fact is photographers skilled in other types of photography that have never shot interiors with a wide angle lens never think about verticals. And most never figure out, by themselves, that it's important to have verticals parallel with the left and right edge of the frame. They have to be told. And some will even argue that it's not important. There is a very accomplished and successful real estate photographer in Australia (that will remain unnamed) that it took me several months in 2007 to convince him that verticals should always be rendered vertical. It's just a concept beginners have a struggle with, but once they become believers they end up spreading the gospel.
Understanding the vertical issue is sort of rite of initiation in interior photography. Once you get your verticals, vertical you can start charging money to shoot interiors!
If you are one of the newbies that still need to know why and how here are some older posts on the subject:
Wow, I didn't realize I'd written so much on this subject.