also: おうがた
凹形の鏡を使うと、像が小さく映る。
When you use a concave mirror, the image appears smaller.
convex shape; convex
Standard kanji spelling for the reading おうけい. The reading おうがた is also used for this form in practice, but Restricted おうけい to 凹形.
Common spelling for the reading おうがた. No restrict おうがた to a specific kanji form is specified, so both 凹形 and 凹型 can be read as おうがた.
Kana spelling is acceptable and avoids kanji ambiguity, especially when the reading おうがた is intended.
Compound of 凹 (concave) and 形/型 (shape/form). The reading おうけい is the on'yomi of the kanji, while おうがた combines on'yomi and kun'yomi. The exact historical derivation is uncertain, but the word is a straightforward technical term.