The curved/fisheye effect is due to a wide angle lens setting compared to the size of the imaging sensor. If you have zoom capability, zoom it in a little and back away from the shot to fill the frame properly. Most of your "all in one" cameras that zoom will go out pretty wide and cause a pretty strong fisheye effect.

The "zooming in" refers to physical lens zooming, not digital zooming like those infernal smart phone cameras. That won't do anything to change the actual focal length of the lens. Unless you have multiple lenses on your phone, you will have the same image focal length, regardless of how little or how much you digitally zoom. I don't know of those phones with a second or third wide angle lens use the same sensor or what, so I don't know if they suffer from image distortion at wide angles. I've never used one.

My smart phone doesn't suffer from the fisheye effect because the imaging sensor is physically very small and matches well with the lens. I'm not familiar with other smart phone cameras. I have a Galaxy S7 and that's the only smart phone photo exeperience I have.

For perspective for you older folks that used to have 35mm SLR film cameras, the optimum lens for no image distortion was about 50mm for the 35mm film size. That gave the most accurate image. Today's digital SLR's with very few exceptions, use a smaller image sensor, so putting the same 50mm lens on it will get you a slight telephoto effect in comparison to a 35mm film camera. My Nikon digital SLR would need a 24mm lens to be equivalent to the 35mm camera image with a 50mm prime lens. Some of your true top of the line professional DSLR cameras have a "full frame" 35mm imaging sensor. They call them FX format cameras. Lenses will perform like they did with the film cameras.

I'm not delving into the aspect ratios other than to mention that 35mm film cameras and FX DSLRs have a 3:2 ratio where DX format DSLRs usually have a 4:3 ratio. I don't know what the "all in one" digitals have, but they are probably 4:3 or maybe even 16:9 ratio. I've never really looked at them.

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