The 20mm series cemented double objective lens, offered in D25F50, D25.5F123, and D23F213 models, is a compact core component for DIY astronomical telescopes. Its cemented double-lens structure optimizes light path transmission, while the anti-reflective coating reduces glare and enhances light transmittance for clear imaging. Designed with a mini standard size, it fits most small-caliber telescope setups, making it ideal for hobbyists building portable observation devices. Made of durable optical glass, it resists scratches and temperature changes, delivering reliable performance for stargazing and astronomical experiments.