I recently completed a roof project for a relative. This was roof #3 for the home- tore off the previous two layers. The home is about 40 years old with roof trusses and 1/2 (maybe 7/16) plywood sheathing, no clips. Plenty of roof and eave ventilation. As expected, the roof deck seemed to be quite brittle. A 220# guy with a bundle of shingles in hand could have stepped through the roof quite easily.
DSLR Definition: Digital Single Lens Reflex Camera. The Nikon D3000 is a DSLR camera. A DSLR, or digital single lens reflex camera is an advanced type of digital camera that provides high-level image quality, performance levels, and manual control options, typically much better than what you'd receive with a fixed lens camera.
DSLR camera bodies are comparatively larger, as they need to fit in both a mirror and a prism. The body of the Nikon D3300, for example, is a rather bulky 3 inches deep before you put the lens on the front. With the 18-55mm kit lens, the camera weighs about 1.1 pounds. A mirrorless camera body can be smaller than a DSLR, with simpler construction. The Sony a5100 has a body just 1.6 inches thick and weighs just over a pound with its 16-50mm kit lens.