A big decision in buying a DSLR camera is the image sensor size. The image sensor is a camera part that photographs the light from the lens to form the image. So, what is a full-frame camera versus a cropped sensor camera?
There are two possible sensor sizes in a DSLR: full-frame and crop-frame (or crop-sensor or cropped sensor). Full-frame DSLR cameras have an image sensor of 36mm X 24mm, usually referred to as 35mm. The name comes from the typical width of film roll which is 35mm. Crop-frame sensors vary in size depending on manufacturer. The Canon Rebel T5i has a cropped sensor of 22.3mm X 14.9, whereas the Nikon D7100’s sensor is 23.5mm X 15.6mm.
Why choose a full-frame DSLR? Full-frame cameras provide better image quality. The quality of megapixels on the sensor is better. They shoot better in low light at higher ISOs. The images produced have less noise. More of an area can be photographed due to the sensor size. There are trade-offs. Full-frame DSLRs cost significantly more than crop-sensor DSLRs. Full-frames are bigger and heavier to carry around. There is an exception, full-frame cameras are now made mirrorless too: reducing the size and weight.
One can also argue to invest more money in higher quality lenses than a higher quality camera body. This debate can go on and on. Keep in mind crop-sensor cameras still provide high-quality images. Cameras only take the image; you make the photo.