Focal Length Measurement Method for Lenses with Small Aperture and Long Focal Length

Fig. 6. Moire fringes near optimal measuring position. (a) Before optimal measuring position; (b) at optimal measuring position; (c) after optimal measuring position

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Table 1. Parameters of lens to be tested
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Table 1. Parameters of lens to be tested
Refractive index Central thickness d₀ /mm r₁ /mm r₂ /mm Aperture D /mm
1.45 8.723 -25000 ∞ 102

Table 2. Comparison of focal-length test with different curvature radiuses

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Table 2. Comparison of focal-length test with different curvature radiuses

No.	r₁=-16800 mm		r₁=-17000 mm
No.	f /mm	Δf/ $\begin{matrix} \bar{f} \end{matrix}$		f /mm	Δf/ $\begin{matrix} \bar{f} \end{matrix}$	f /mm	Δf/ $\begin{matrix} \bar{f} \end{matrix}$
1	-33216.2		0.0080%	-33243.3	-0.0273%	-33212.4	-0.0531%
2	-33210.0		-0.0107%	-33262.9	0.0317%	-33240.6	0.0317%
3	-33219.9		0.0191%	-33262.8	0.0314%	-33221.6	-0.0254%
4	-33222.1		0.0257%	-33250.2	-0.0065%	-33247.2	0.0516%
5	-33203.8		-0.0294%	-33243.5	-0.0267%	-33212.3	-0.0534%
6	-33222.8		0.0279%	-33246.7	-0.0170%	-33228.3	-0.0053%
7	-33203.8		-0.0294%	-33268.9	0.0497%	-33237.5	0.0224%
8	-33209.8		-0.0113%	-33240.6	-0.0354%	-33240.5	0.0314%
$\begin{matrix} \bar{f} \end{matrix}$			-33213.5		-33252.4		-33230.6

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Lei Zhao, Jian Bai, Weidong Fang. Focal Length Measurement Method for Lenses with Small Aperture and Long Focal Length[J]. Acta Optica Sinica, 2020, 40(4): 0412002

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