I am sure Ron will correct me if I am wrong, but I think a lot of it has to do with the fstop setting that your camera uses. The smaller your aperature is will result in better depth of field and less fisheye. That basically means, if you put a whole lot of light on the subject, the better and more accurate your pictures will be. Your DSLR will automatically select the proper balance of fstop and shutter speed to get the light levels right. If you shoot in low light, it will open the aperature more so that the shutter speed will be reasonable so as to eleminate blur of somebody shooting the shot without a tripod. If you want to shoot in low light conditions, I recommend the use of a tripod and manual settings for best results.
-Stu
The f stop controls the amount of light through the lens in one respect. The bigger the number the smaller the hole. The smaller the hole the longer the range of in focus subject matter.
The other control for the amount of light is the shutter speed. The longer the shutter (not rely a shutter on digital ) is open the more light. So you can get the same ratio
( exposure) by a combination of settings. The light meter does not see color just a range of tones from black to white. It averages all these tones to a medium grey and sets the exposure from that so it can be easily fooled if there is an excess of light or dark area in the shot. On automatic, it has no idea of whether you are trying to have things in focus for a long distance, depth of field, or a short distance. So the depth of focus is effected by the f stop as well as how far you are from the subject you, or the camera thinks you want to be focused on. Todays cameras have various ways to focus, overall, spot, center weighted, etc. but you have to tell it what you want. Cameras are dumb, they can't read your mind, so they just take average pictures unless they are given a little "command and control"
Most folks can hold a camera steady down to 1/60th of a second or less if they stand still, hold the camera properly and don't breath hard, so unless the subject is moving across the field of view, side to side, it is much better to use the "AV" setting. That lets you control the hole size and depth of field and the meter will choose the shutter speed to give an average exposure.
"AV" is the most used setting in photography because it puts you in control to give the focus depth you want.
The shutter speed is always shown in the viewfinder so if it is too slow you just open up the f stop a little. If you measured the amount of light for each f stop it will double each time you go down from f22 to f16 to f11 to f8 etc.
Most cameras and lenses, especially Zoom lenses have a "sweet spot" meaning they take the best pictures at a certain zoom range and a certain f stop. The rest are not as good going either way.
Most wide angle and zoom lenses set to wide angle do have distortion, usually barrel distortion. Very wide angle lenses have a distortion known as fisheye.
Some of the newer high end ultra small cameras that have fantastic features have terrible lens distortion, so much so that unless you use the software that comes with them
the pictures are terrible. Even Photoshop has not been updated to fix the distortion very well.
So that's the short answer to your question
I could go on for months as photography has been one of my main hobbies since I was a kid and developed and printed pictures in the basement.
Peters camera does have some barrel distortion at wide angle settings but like he said in the picture of the ceiling only one side is bowed and it is not in the center of view.
It could be light reflection giving the look of a bowed ceiling but the only way to know is with measurements, strings, levels, lasers, etc. The bottom of the sloped trusses wouldn't have to be off much to change the height.
If they missed lining up the ridge tips on the trusses a little you wouldn't see it because of the ridge vent. The roof might have a hump on one side and a depression on the other, but that would be very hard to see without stretching a very tight string across the roof at various levels front and back.
Once the room is furnished and dolled up folks aren't going to be staring at the ceiling anyway, so it is a moot point, except for a possible discount in house value.
I have lost track on the 16" of cellulose insulation above the ceiling. Has it been blown in yet?
Ron