Each lens has a unique optical profile which serves a purpose in allowing you to see varying fields of view at various magnifications. These two parameters (Field of View and Magnification) provide different advantages depending on the use case. Although some lenses can provide you with a good balance of magnification & field of view, no single lens will provide you with everything. For example, a wide field lens will help you scan a larger area quickly, perfect for general diagnosis and as a first pass retinal exam. Higher magnification lenses are used when you are examining the optic nerve head, macula or noticed something during a wide field exam that you want to examine more closely. Lenses like the 20D, 90D, and 78D are usually the first lenses you will learn on, as they provide a good balance of field of view and magnification and will help you master the technique of lens handling. As you gain more proficiency, adding more lenses will make you more effective. You don't necessarily need every "club in the bag", however you do need more than a driver!
Lens Education