The camera you have is a great camera. But it’s full of advanced features some of which are customizable. As far as lenses go Canon is no longer making any new EF lenses. Though used lenses can be found. But service life is running out for most lenses. If you own any EF-S lenses from your digital Rebel. They will NOT be compatible with a Full Frame Camera such as the EOS 5D Mark IV. EF-S lenses are designed in a way to prevent mounting on a Full Frame DSLR or EOS film SLR. Now 3rd Party lenses use different names to differentiate between Full Frame and APS-C. So look closely at the description. 3rd Party lenses for APS-C will mount but won’t cover the entire image sensor. It will look like you shot through a pipe. Black areas in all 4 corners. Or you’ll cause serious damage to the camera’s mirror. Any Full Frame Canon EF lenses that you used with your Digital Rebel are compatible. Just know that AF speed, IS, Aperture and performance vary depending on the lens. Most EF lenses are professional grade lenses and will have “L” after the aperture value in the name. This “L” is colored red and stands out. Such as the lens you own which is the EF 24-105mm F/4L IS II USM lens. That is great standard zoom lens for Full Frame cameras. Though there are older consumer grade EF lenses that are not professional grade. Also there is no built in flash on Full Frame cameras. So an external speedlite is needed for flash photography. Any older Canon EX model speedlite will work with your camera.
-Demetrius
Bodies: EOS 5D Mark IV
Lenses: EF Holy Trinity, EF 85mm F/1.8 USM
Speedlites: 420EX, 470EX-AI, 550EX & 600EX II-RT
