Tobias Porsch | TechnoTeam: What is the optical trade-off between using a physical aperture versus a virtual projected pupil in near-eye display metrology?
03:32 - 05:39
Other snippets from this talk
Summary of the clip:
What is the optical trade-off between using a physical aperture versus a virtual projected pupil in near-eye display metrology?
Eye size and adaptation, the mechanical layout and entrance pupil aspects have been standardized for many years. In this lens design, a physical aperture is attached to the front of the lens, at exactly the location where the optical aperture sits in the design. Because of the case, the lens stays attachable and exchangeable, and pupil-size restriction is achieved by the aperture cap at that designated optical position.
Adding an internal aperture instead projects a virtual pupil before the lens. When configuring this internal aperture, different free working distances and virtual pupil diameters can be projected. But this approach also has drawbacks: a virtual aperture with larger working distance and larger diameter results in a smaller vignetting-free field of view, so both parameters cannot be pushed up without cost to the usable flat field.
The trade-off is plotted with free working distance on the X-axis and the resulting flat-field usable field of view on the Y-axis. Each coloured line presents a different diameter of the created virtual entrance pupil. With increasing diameter, the residual flat field of view that can be used becomes smaller. That is the core optical compromise when choosing between a physical aperture and a projected virtual pupil.
In this short video, you can learn:
* A physical aperture sits at the front of the lens, exactly where the optical aperture is located in the design, so pupil size is restricted by an exchangeable aperture cap.
* An internal aperture projects a virtual pupil before the lens, allowing different free working distances and virtual pupil diameters to be configured.
* Larger virtual working distance and virtual pupil diameter shrink the vignetting-free field of view, reducing the residual flat field available.
📋 **Clip Abstract** Near-eye display metrology standardises eye size, adaptation, mechanical layout and entrance pupil, with a physical aperture placed at the front of the lens at the optical aperture position. Replacing it with an internal aperture projects a virtual pupil that offers configurable working distances and diameters, but larger values shrink the vignetting-free field of view and the usable flat field.
About the speaker:
* Speaker: Tobias Porsch
* Company: TechnoTeam
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#EntrancePupil, #ApertureCap, #VirtualPupilProjection, #VignettingFreeFOV, #NearEyeDisplayMetrology, #XROpticalMetrology
This is a highlight of the presentation:
Biomimetic Metrology Lenses for Near-Eye Displays: Diffraction-Limited AR/XR Quality Assurance
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01:13 - 03:05
How does the eye's 47 line pairs per degree foveal limit set MTF criteria for XR metrology lenses?
How does the eye's 47 line pairs per degree foveal limit set MTF criteria for XR metrology lenses?
The human eye is the reference XR metrology instruments must measure up to. Its sensitivity has to be matched by those instruments, and this is captured, filed and traceable in photometric specifications. For near-eye display tasks, eye geometry adds pupil adaptation and rotational movements when viewing into a headset. These parameters frame what a metrology system must reproduce.
The foveal resolution figure comes from a recent study by Meta Reality Labs and the University of Cambridge, published last year. They remeasured the human eye's foveal resolution limit at up to 47 line pairs per degree, for achromatic viewing conditions. It is taken as a conservative benchmark. To measure XR headset optical resolution correctly, optical systems are optimized to meet the resulting MTF criteria.
Distortion is another parameter. The human eye's distortion perceptibility depends on its magnitude, consistency between both eyes, and how abruptly it varies locally across the field. A systematic evaluation and comparison of these optical parameters across various lens designs requires a defined set of methodological performance metrics. Without defined metrics, comparing distortion, resolution and eye-geometry effects across XR lens designs stays inconsistent.
In this short video, you can learn:
* The human eye is the reference for XR metrology, with sensitivity captured and traceable in photometric specifications.
* Meta Reality Labs and University of Cambridge remeasured foveal resolution at up to 47 line pairs per degree for achromatic viewing.
* XR headset resolution is measured against MTF criteria from that conservative benchmark; distortion perceptibility depends on magnitude, consistency between both eyes and abrupt local variation.
📋 **Clip Abstract** The clip frames the human eye as the reference for XR metrology, from sensitivity traceable in photometric specifications to eye geometry from pupil adaptation and rotational movements. It cites a Meta Reality Labs and University of Cambridge study measuring foveal resolution at up to 47 line pairs per degree for achromatic viewing, applies that conservative benchmark to MTF criteria, and discusses distortion perceptibility and the need for defined performance metrics across lens designs.
About the speaker:
* Speaker: Tobias Porsch
* Company: TechnoTeam
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#FovealResolution, #LinePairsPerDegree, #MTFCriteria, #PhotometricSpecifications, #NearEyeDisplays, #OpticalMetrology
10:53 - 13:18
How can liquid lenses overcome focus-induced pupil shifts and maintain MTF stability over thousands of cycles in XR metrology?
How can liquid lenses overcome focus-induced pupil shifts and maintain MTF stability over thousands of cycles in XR metrology?
Standard lens focus involves compromises: the entrance pupil position may shift when focusing, optical resolutions change with lens alignment, and undefined geometrical projection and distortions arise from field-of-view changes. A liquid lens design addresses these problems. Yet imaging reproducibility is questioned because liquid lenses are widely known to have unstable optical properties. The approach uses high-quality liquid lenses, passive gravity compensation, and paraxial viewing conditions, meaning only a smaller inner part of the diameter is used.
These tricks minimize the problems, and the system is tested for them. Focus stability and repeatability are tested under different alignment conditions, horizontal or vertical alignment, on axis and in the field. Validation uses MTF measurements over time. MTF is very sensitive to slight defocus. Data include a static focus test and a repeated refocus test. Over 48 hours and over 6,000 image captures, the MTF curves remain stable.
Finally, geometrical distortion is the last requirement. The human eye's perceptibility is focus independent and based on local magnitudes. The liquid lens approach minimizes the stated compromises through high-quality liquid lenses, passive gravity compensation, and paraxial viewing conditions, using only a smaller inner part of the diameter. Focus stability and repeatability are validated under different alignment conditions, on axis and in the field, via MTF measurements. Over 48 hours and 6,000 image captures, MTF curves remain stable.
In this short video, you can learn:
* Standard lens focus shifts entrance pupil position, changes resolution with alignment, and introduces undefined projection and distortion from field-of-view changes.
* High-quality liquid lenses with passive gravity compensation and paraxial viewing conditions, using a smaller inner diameter, minimize known instability and are tested for focus stability and repeatability.
* MTF measurements over time, including static and repeated refocus tests, remain stable across 48 hours and 6,000 image captures; geometrical distortion perceptibility is focus independent and based on local magnitudes.
📋 **Clip Abstract** Standard lens focus compromises include entrance pupil shifts, alignment-dependent resolution changes, and field-of-view distortion; a liquid lens design addresses these with high-quality components, passive gravity compensation, and paraxial viewing conditions. MTF testing validates focus stability and repeatability over different alignments, remaining stable over 48 hours and 6,000 image captures; geometrical distortion perceptibility is focus independent and based on local magnitudes.
About the speaker:
* Speaker: Tobias Porsch
* Company: TechnoTeam
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#LiquidLensDesign, #PassiveGravityCompensation, #MTFMeasurements, #FocusStabilityTesting, #NearEyeDisplays, #ARXRQualityAssurance
08:28 - 10:34
Why must near-eye display metrology lenses achieve diffraction-limited MTF performance up to the human eye's 47 lp/deg limit?
Why must near-eye display metrology lenses achieve diffraction-limited MTF performance up to the human eye's 47 lp/deg limit?
The instrument's MTF must be nearly diffraction-limited because the XR display under test and the metrology lens form a phase-coupled system. Their MTF curves interact, so a clean reconstruction of the device's MTF is impossible if the lens is not diffraction-limited. The diffraction-limited behavior only needs to extend to the human eye's resolution limit: the Meta and Cambridge study places that at 47 line pairs per degree. Beyond it, the eye cannot distinguish brightness differences that well.
The diffraction limitation is primarily realized on axis and is measured and validated for a specified field of view and over the whole focal range of the lens. Curves at different focal lengths show on-axis and in-field behavior. Thus, only a defined part of the available field of view fulfills the diffraction-limitation criterion. The limitation also depends on pupil size, so it is realized only for specified aperture diameters. Larger aperture numbers make a diffraction-limited optical design harder to achieve.
A six-millimeter aperture diameter is further from diffraction limitation and is better than optical resolution, but it is no longer diffraction limited according to the specification. The next design request is the focal range. These constraints mean diffraction-limited metrology up to the eye's limit is not a compromise; it is a defined, bounded requirement tied to axis, field of view, aperture, and focal range.
In this short video, you can learn:
* The XR display under test and the metrology lens form a phase-coupled system, so their MTF curves interact.
* Diffraction-limited metrology is only required up to the human eye's 47 line pairs per degree resolution limit.
* Diffraction limitation is realized on axis, for a specified field of view, focal range, and aperture diameter, with a six-millimeter aperture no longer meeting the specification.
📋 **Clip Abstract** Metrology lenses for near-eye display testing must be nearly diffraction-limited because the lens and XR display form a phase-coupled system whose MTF curves interact. The required diffraction-limited behavior extends only to the human eye's 47 line pairs per degree limit, and is realized on axis for a specified field of view, focal range, and aperture diameter, with a six-millimeter aperture failing the specification.
About the speaker:
* Speaker: Tobias Porsch
* Company: TechnoTeam
* Event: Eindhoven 2026
* Location: High Tech Campus, Eindhoven
#PhaseCoupledMTF, #DiffractionLimitedLens, #47LinePairsPerDegree, #SixMillimeterAperture, #OpticalMetrology, #XRDisplayTesting