You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lens.go
    path of file: ./repos/photoprism/internal/entity
    
    the code of the file until where you have to start completion: package entity

import (
	"strings"
	"sync"
	"time"

	"github.com/photoprism/photoprism/internal/event"
	"github.com/photoprism/photoprism/pkg/clean"
	"github.com/photoprism/photoprism/pkg/txt"
)

var lensMutex = sync.Mutex{}

// Lenses represents a list of lenses.
type Lenses []Lens

// Lens represents camera len
    
func NewLens(makeName string, modelName string) *Lens {
	makeName = strings.TrimSpace(makeName)
	modelName = strings.TrimSpace(modelName)

	if modelName == "" && makeName == "" {
		return &UnknownLens
	} else if strings.HasPrefix(modelName, makeName) {
		modelName = strings.TrimSpace(modelName[len(makeName):])
	}

	// Normalize make name.
	if n, ok := CameraMakes[makeName]; ok {
		makeName = n
	}

	// Remove duplicate make from model name.
	if strings.HasPrefix(modelName, makeName) {
		modelName = strings.TrimSpace(modelName[len(makeName):])
	}

	// Remove ignored substrings from model name.
	modelName = LensModelIgnore.ReplaceAllString(modelName, " ")

	var name []string

	if makeName != "" {
		name = append(name, makeName)
	}

	if modelName != "" {
		name = append(name, modelName)
	}

	lensName := strings.Join(name, " ")

	result := &Lens{
		LensSlug:  txt.Slug(lensName),
		LensName:  txt.Clip(lensName, txt.ClipName),
		LensMake:  txt.Clip(makeName, txt.ClipName),
		LensModel: txt.Clip(modelName, txt.ClipName),
	}

	return result
}