In daily astronomical shooting, the backfocus will have an influence. Astronomical photographers are often frustrated by the change of backfocus due to various reasons such as refraction of filters or when using some products with sensitive backfocus. To solve this problem, ASKAR launched the backfocus adjuster, (providing the adjustment range from 16mm-20mm), which can be adjusted ± 2mm of the backfocus. We offer two specifications for the backfocus adjuster, t