Selection guide
1951 USAF resolution calculator
Convert a USAF 1951 group and element to pattern frequency and nominal bar width.
Pattern reference
- Pattern frequency
- 8.0000 lp/mm
- Line-pair period
- 125.0000 µm
- Nominal width of one bar
- 62.5000 µm
Frequency = 2group + (element − 1) / 6 lp/mm. A line pair comprises one light bar and one dark bar; its period is 1 / frequency mm.
This gives the target pattern dimensions, not the achieved resolution of a lens or camera. The finest resolved element depends on the imaging setup and observation criterion. Use only patterns explicitly identified as USAF 1951; do not apply this formula to another reticle pattern. The group range here is a calculation range, not a statement of available PHOSLENS targets.
Formula reference: USAF 1951 group/element relationship.