Yes, it is legal
Vivitar sell a digital SLR camera that is a 35mm model which can be purchased at Urban Outfitters and is touted as a great camera for either beginners or professionals.
All major camera companies make SLR cameras, as well as digital SLR cameras. My photography teacher always recommended the Promaster 2500PK Manual SLR camera for its ease of use, value, and manual functions.
You can go to Best Buy's GEEK squad and have them assist you with slr cameras. Another option is to go to Amazon.com or Wiki to research your preferences.
One can purchase lenses for SLR cameras through online retailers such as Amazon or eBay. Alternatively, one could purchase SLR camera lenses at a physical store such as Best Buy.
Digital SLR referes to "digital single-lens reflex." This terminology is often used when speaking about cameras. Such cameras can allow the photographer to change lenses as he or she sees fit.
Portability and cost.
Nikon
No, not All of them do.
Single Lens Reflex. It has to do with cameras.
SLR and Point-and-Shoot cameras
No, film single lens reflex (SLR) cameras exist, albeit obsolete. Currently all commercial single lens reflex cameras are digital, however, it may be possible to find a retailer or more likely, a private seller in possession of a functional film SLR camera.
SLR digital cameras are professional grade cameras which have settings which may be manipulated to produce outstanding photos that otherwise could not be achieved with a regular digital camera