Optics Lens Calculator

Image Type is "Real" whenever Image Distance comes out positive, meaning the image forms on the opposite side of the lens from the object -- light rays actually converge there, so a real image can be projected onto a screen or captured on a camera sensor. Image Type is "Virtual" whenever Image Distance is negative, meaning the image forms on the same side as the object; light rays only appear to diverge from that point, the way a magnifying glass creates an enlarged image you can only see by looking through the lens, never project onto a wall.

Focal Length's sign tells the calculator whether you're modeling a converging (convex, positive focal length) or diverging (concave, negative focal length) lens. Diverging lenses -- used in some corrective eyewear and certain camera designs -- always produce a virtual, upright, reduced image of a real object, regardless of how far away the object sits, because the thin lens equation with a negative f can never produce a positive Image Distance for a positive Object Distance.

Not consistently -- neither Focal Length nor Object Distance dominates Image Distance's sensitivity across this calculator's full declared ranges. Which one matters more at any given moment depends on how close the current values sit to the singularity at Object Distance = Focal Length, where the denominator (do − f) approaches zero and sensitivity to both inputs spikes sharply. Near this calculator's shipped default values Focal Length happens to have the larger effect, but sampled across the full input range Object Distance actually comes out ahead more often -- so don't treat either input as the unconditionally dominant one; the answer depends on where you are in the range.

The thin lens equation's denominator (Object Distance − Focal Length) goes to zero, which is the classic "object at the focal point" case: rays leaving the lens emerge parallel and never converge to form a finite image at any distance. This calculator won't hit that exact case from its default inputs, but it's worth knowing as the mathematical edge of the model -- image distance grows without bound as Object Distance approaches Focal Length from either side.

No -- the relationship isn't monotonic across the lens's full working range. Near typical operating points moving the object farther away changes magnification one way, but because the equation passes through the singularity at Object Distance = Focal Length, the trend can reverse elsewhere in the input range. Treat Magnification as a precise answer for your specific entered values rather than assuming a simple "farther object, smaller image" rule holds everywhere.