Optical System Lens Design for Color Aberration and Focus Shift
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Solution Overview
Problem
Existing optical systems for image pickup devices and image projection apparatuses face challenges in correcting color aberration and focus shift due to temperature variations, particularly when compact size and high optical performance are required, as current methods either fail to adequately address axial color aberration or result in significant focus position shifts.
Innovation Solution
The optical system employs at least two first positive lenses and one second positive lens, strategically positioned relative to an aperture stop, with specific refractive index and dispersion characteristics to correct color aberration and focus shift, using lenses with Abbe numbers and refractive index changes that satisfy specific conditional expressions to maintain image quality across temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a lens holding barrel with material having a coefficient of linear expansion is used to correct focus shift due to temperature variation, then the focus position shift can be compensated, but the apparatus size increases and material selection is limited
Solution Approach 1:
The invention changes the refractive index parameter of the lens material with temperature to achieve focus correction. By selecting optical glass with specific temperature coefficients of refractive index (dn/dT), the lens automatically adjusts its optical power in response to temperature changes, compensating for focus shift without requiring thermal expansion of mechanical structures.
Solution Approach 2:
The invention uses composite optical systems combining multiple lenses made of different optical glasses with complementary temperature characteristics. By pairing lenses with positive and negative temperature coefficients of refractive index, the system achieves thermal focus compensation through optical design rather than mechanical expansion, avoiding the need for specialized expanding materials in the lens barrel.
2Manufacturing precision
If optical glass with anomalous dispersion characteristic is used to correct color aberration, then axial color aberration is reduced, but focus position varies during zooming due to temperature variation
Solution Approach 1:
The invention applies different optical glass materials with specific temperature characteristics to different lens elements based on their local requirements. Lenses where temperature-induced focus shift needs to be minimized are made from glass with low dn/dT values, while other elements use glass optimized for color aberration correction. This localized material selection allows simultaneous optimization of both color correction and focus stability.
Solution Approach 2:
The invention converts the harmful effect of temperature-induced refractive index changes into a beneficial focus compensation mechanism. By carefully selecting optical glasses with specific temperature coefficients, the natural thermal response of the lens materials is harnessed to automatically compensate for focus shift, turning what was previously a problem into a solution.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration effectively corrects color aberration and suppresses focus position shifts due to temperature variations, ensuring high image quality and stability across the entire zoom range, even under high temperature conditions commonly found in image projection applications.
Implementation Method 1
at least two first positive lenses satisfying the following conditional expressions (1) to (3) are disposed closer to a contraction side than an aperture stop, and at least one second positive lens satisfying the following conditional expressions (1), (4) and (5) is disposed
Implementation Method 2
as a method of correcting such focus shift due to temperature variation, there is known a method of using thermal expansion of a lens barrel which holds the lenses
Data Source
AI summary
Provided is an optical system (PS) which is used in a wavelength range including a near ultraviolet light range having a wavelength longer than approximately 350 nm and a visible light range. The optical system includes at least two first positive lenses which satisfies a predetermined conditional expression concerning anomalous dispersion characteristic and a rate of change of the refractive index with respect to temperature, and is disposed closer to a contraction side than an aperture stop (ST), and at least one second positive lens which satisfies a predetermined conditional expression concerning anomalous dispersion characteristic and a rate of change of the refractive index with respect to temperature.