Magnification: 3.5x
Numerical Aperture: 0.1
Infinity-corrected optics (requires tube lens)
Compatible tube lens focal length: 200 mm
Thread diameter and pitch: M26 x 0.706
Weight: 210 g
Housing length: 54.07 mm
Housing diameter: 34 mm
Parfocal distance (housing length plus working distance): 95 mm
Focal length: 57.1 mm
Working distance: 40.93 mm
Resolution: 2.75 µm
Depth of field: 27.5 µm

Imaging Performance – 208 mm Tube Lens

The following test images illustrate the optical performance of the lens. The first shows an overview shot (full-frame sensor) using the Raynox DCR 150 tube lens, resulting in an approximate nominal magnification of 3.5x. The two subsequent images each show a magnified crop.

Test image at nominal magnification (DCR 150), with frame markers for the following cropped enlargements – the slight darkening in the corners indicates that the lens’s image circle is slightly exceeded by the full-frame sensor. However, no pincushion distortion is yet noticeable.

Sharpness in the image center is most evident in the small square box structures, and the rendering of extremely fine details corresponds to what can be expected from a relatively affordable lens at this low magnification—though it is not particularly spectacular.

Toward the image corners (in this case, upper left), a slight decrease in sharpness becomes apparent, along with hints of chromatic aberration. Contrast also begins to flatten. In the peripheral zone, the lens’s image circle is clearly exceeded.

The test image of the HLB M Plan Apo 3.5x on a full-frame sensor delivers an overall nuanced and, in many areas, convincing result. However, optical performance varies depending on the position within the image field—ranging from very solid in the center to somewhat limited toward the edges. The following is an evaluation by zones:

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Center

In the image center, the HLB 3.5x demonstrates impressively good optical performance. The fine circuit structures of the test target are clearly separated, lines appear with well-defined edge sharpness, and microcontrast is quite respectable—especially considering the moderate numerical aperture of 0.1. There are no distracting color fringes or center-field distortion. Detail rendering is smooth and natural, without exaggerated edge sharpening. For a lens in this class, it delivers stable and reliable reproduction, capable of resolving even demanding subjects in the central image area with clarity.

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Extended Center

Outside the absolute center, resolution begins to decrease slightly—an expected behavior. Line contrast drops, and very fine structures gradually start to merge. However, depth of field remains consistent, and field flatness appears well controlled. Transitions toward the edge areas are smooth, not abrupt, indicating thoughtful optical correction. In this extended zone, detail rendering remains usable for most applications, though with a slightly reduced level of differentiation.

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Edge Zone

In the edge zone, the decline in image quality becomes noticeable. Fine circuit patterns begin to overlap more, and both contrast and resolution drop significantly. There are no harsh distortion artifacts, but edge sharpness is clearly reduced, and darker areas tend to appear slightly “muddier.” Chromatic aberration remains well controlled, with only minimal color fringing. Notably, the lens does cover the full image circle—despite limitations, the geometric projection remains stable all the way to the corners.

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Overall Impression

In its specified configuration, the HLB M Plan Apo 3.5x delivers overall good performance, particularly in the center and extended center zones. The outer areas exhibit the expected weaknesses for a lens with only 0.1 NA on a full-frame sensor, yet they remain free from major optical defects. For many technical applications—such as centrally positioned subjects, typical stacking scenarios, or measurement series—this lens is a practical and usable solution.

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However, those seeking uniform edge-to-edge sharpness at maximum resolution—e.g., for precise structural analysis across the entire field—would be better served with objectives featuring a higher NA or by using a smaller sensor format. Within its optical class, though, this lens shows a solid, reliable profile—with forgiving behavior in focus stacking and usable performance even for documentation purposes in the extended image field.

Imaging Performance – 125 mm Tube Lens

The following test image is another overview shot, this time taken with the Raynox DCR 250 tube lens, which reduces the magnification to approximately 2.19x (instead of 3.5x). Some metallurgical microscope objectives from the mentioned HLB series tolerate this approach, although not all to the same extent. This test aims to evaluate what qualitative compromises can be expected when using the Mitutoyo M Plan Apo 3.5x under these conditions.

Test image with DCR 250: In this combination, image sharpness at the center is only moderate and significantly lower than at the nominal magnification. Outside the image center, sharpness drops off dramatically. A slight pincushion distortion is also noticeable. Darkening in the edge and corner areas is more pronounced compared to using the DCR 150.

The image center still retains a certain level of sharpness, but the finest details are no longer resolved when using the DCR 250.

The edge zone exhibits strong pincushion distortion and intolerable blurriness, which becomes extreme toward the corner (here, upper left). On a full-frame sensor, this combination of objective and tube lens is simply unusable.

In the image shown here, taken with the HLB M Plan Apo 3.5x on a full-frame sensor using a tube lens with only 125 mm focal length, the impact of deviating from the specified configuration (200 mm) on the lens’s optical performance is clearly evident. The rendering across the entire image field is noticeably altered—partly due to the change in magnification, and partly due to imaging errors introduced by the unsuitable tube lens. The detailed assessment is as follows:

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Center

In the center of the image, the optical quality remains usable, though clearly below the level the lens delivers with the correct 200 mm tube lens. Edge sharpness is softer, lines appear slightly smudged, and microcontrast is reduced. Fine details begin to blur together, especially in areas with low contrast. However, the plane of focus still appears stable—there is no overlapping or astigmatism in the center, indicating that field flatness remains reasonably intact.

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Extended Center

Already in the extended center zone, the loss of correction becomes noticeable. Line structures appear duller and less defined, local contrast drops significantly, and early signs of field curvature and blur extension appear. Homogeneous detail rendering declines, and resolution falls visibly short of what the lens delivers with a 200 mm configuration. The differences are substantial enough to negatively affect technical applications such as measurement or structural analysis.

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Edge Zone

In the edge areas, the lens exhibits pronounced optical degradation in this setup. Blurriness increases significantly, and line structures lose almost all edge definition. Particularly striking is the loss of contrast and local detail rendering, resulting in a dull and sometimes washed-out appearance. In the lower edge region, vignetting effects also appear to be present, visibly limiting the image circle—a typical issue with infinity-corrected optics when used with significantly shorter tube focal lengths. Originally corrected for a 30 mm image circle, the lens no longer adequately covers this area in the current setup.

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Overall Impression

This image clearly demonstrates that the HLB M Plan Apo 3.5x, when used with a 125 mm tube lens, is operating well outside its optimal performance range. The theoretical reduction in magnification to approximately 2.19x not only alters the image geometry but also disrupts the optical correction: sharpness, contrast, and field performance all visibly deteriorate across the image, with the most severe losses occurring toward the edges.

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For technically precise applications or high-quality focus stacking on full-frame sensors, this configuration is not recommended. To fully utilize the potential of the lens, it is best to adhere to the specified 200 mm tube lens. While even at that setting the corners are not perfect, the image is significantly better corrected and centrally stable—making it suitable for many practical applications. Use with a 125 mm tube lens, on the other hand, remains a visible compromise that consistently affects image quality.

Comparison HLB M Plan 3,5x – Canon MP-E 65 mm – Tube Lens 208 mm

The direct comparison with the Canon MP-E 65mm macro lens at the 3.5x setting is intended to show how the HLB M Plan Apo 3.5x performs alongside this highly sharp macro specialist. Shown above is the upper right quarter of each respective full image.

HLB M Plan Apo 3.5x (left) compared with the Canon MP-E 65mm at 3.5x (right). The top row shows the upper right quarter of the original full-frame image (focus stack), while the bottom row shows a sixteenth of the original image, scaled up accordingly.

The image field of the HLB lens (top left) shows an overall uniform and stable optical performance, especially considering its moderate numerical aperture of 0.1. In the center (bottom left of the top left image), the lens impresses with clean line rendering, good separation of fine structures, and nuanced contrast transitions. Even in the magnified detail view (bottom left), the image remains stable—the circuit traces are clearly defined, microcontrast is restrained but clean.

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In the extended center area, the lens maintains its performance level, but at the edge (top right of the top left image), resolution visibly begins to decline. Lines become softer, details start to blend, and contrast decreases. Nevertheless, the image field remains forgiving: there are no significant aberrations such as chromatic fringing, astigmatism, or distortion. The structure remains visible, albeit with reduced precision.

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In direct comparison (top right), the Canon MP-E 65mm at 3.5:1 delivers noticeably crisper detail in the edge region: the circuit patterns appear slightly sharper, microcontrast is higher, and lines show less merging than with the HLB. While the Canon’s optical performance also drops toward the edges, it remains more stable overall than that of the HLB.

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In the center (bottom left of the top right image), the Canon also performs well but appears slightly coarser—it exhibits stronger edge contrast, though with reduced nuance in fine structures. The detailed view (bottom right) reinforces this impression: the image looks “bolder” but not necessarily more highly resolved. The structures appear denser and more harshly rendered, but less finely separated than with the HLB.

Evaluation

Overall Impression
The comparison presents a balanced picture of two very different lens concepts. Under ideal conditions (200 mm tube lens, full-frame sensor), the HLB M Plan Apo 3.5x delivers consistent and well-corrected performance with only a slight drop in quality toward the edges, but overall strong uniformity. The Canon MP-E 65mm, on the other hand, at the same magnification, shows a slightly denser but less differentiated rendering in the center—yet clearly surpasses the HLB in edge sharpness.

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For technical applications requiring high edge resolution, the Canon remains optically competitive despite its age—especially given its flexibility. The HLB, however, stands out for its even field performance, flat-field rendering, and exceptionally long working distance—typical strengths of a precision-engineered industrial objective.

Considering the price (in 2025, the HLB costs significantly less than half of the Canon MP-E), it offers a remarkably good price-performance ratio, particularly for users who prioritize smooth, distortion-free image structure. The Canon remains a versatile macro solution that shines in scenarios where maximum sharpness under flexible shooting conditions is critical—especially at the edges.