Focus topic. The HP/15 builds on two decades of proven HP/11 performance for digital detectors, in-line inspection and CT.
September 21, 2026
For two decades, the HP/11 has been the reference minifocus X-ray tube for high-resolution and high throughput radiography. The HP/15 keeps everything that made it trusted, and reengineers the rest for digital detectors, in-line inspection and computed tomography.
Inspection changed, the source had to follow
Three shifts reshaped industrial NDT over the last twenty years. Together they changed what an X-ray source has to deliver, and exposed where the legacy design reached its limits.
1
Film → digital detectors
Digital detector arrays (DDAs) have a coarser pixel pitch than film, so more geometric magnification is needed. That demands a smaller, cleaner focal spot — without sacrificing power.
2
Single shots → in-line & CT
Throughput and 3D reconstruction reward a broad, even beam and a focal spot that stays homogeneous across the full emission angle, not only on the central ray.
3
Occasional → continuous use
Inspection now runs around the clock at high duty cycles, making thermal robustness and uptime as decisive as raw image quality.
The HP/15 answers all three:
A cleaner, more symmetric focal spot for sharper images, a wider usable beam for more speed, and two focal spots for built-in uptime.
70%+
Larger usable beam area (50°×40° vs 40°×30°)
2x
Identical, thermally separated focal spots for redundancy
0
Workarounds, even resolution without tilting the tube
Why the HP/11 became the reference
When digital detectors arrived, geometrical magnification became essential, something film never required. The HP/11 was engineered to make that possible. Film has very high intrinsic resolution and can sit directly against the part, so even a relatively large focal spot produces sharp radiographs. Digital detectors changed the rules. Their larger pixel pitch means the image must be magnified geometrically to recover detail, and the moment you magnify, the size of the focal spot starts to blur every edge. That blur is geometric unsharpness: the focal spot is not a point, so each feature casts a penumbra whose width grows with magnification and with focal-spot size.
To magnify and stay sharp, you need a small focal spot — but a small spot concentrates heat on a very small area of the target, which limits power and therefore speed. The HP/11 resolved that tension with three coordinated design moves: a redesigned target topology and cooling system, a carefully chosen target angle that keeps the heated area large while projecting a small optical spot, and redesigned electron optics to shape the beam. The result, small spot, high power, became a de facto industry reference, adopted across the market.
One spot, two sizes
The thermal focal spot is the real area heated by the electron beam on the target. The optical focal spot is what the detector “sees”, that area projected toward the image. By tilting the target, a large heated area is foreshortened into a small projected spot. This is the central trick of every minifocus tube: spread heat over a large thermal spot (more power, longer life) while presenting a small optical spot (sharp images). The art is doing it without distorting the spot or starving the beam at the edges of the field — exactly where the HP/11 left room to improve.
An imperfect focal spot
The HP/11 small spot carries satellites “wings” at top and bottom. They add unsharpness and make resolution unequal depending on the orientation X or Y.
Half the tube, unused
Today’s applications run almost exclusively on the small focal spot, so the HP/11’s large spot is rarely put to work.
A tilting workaround
Most users tilt the tube ~4–5° toward the cathode to even out dose, which stretches the focal spot and trades away sharpness.
Downtime hurts
When a tube degrades, the whole inspection line can stop. Unplanned replacement is costly in both parts and lost production.
A cleaner spot is the foundation of a cleaner image
Resolution starts at the source. The shape of the focal spot is printed into every radiograph and every CT slice. The HP/11 small spot is very compact in the X direction but elongated in Y, where the wings live. Because unsharpness follows the spot’s shape, edges perpendicular to one axis come out sharper than edges perpendicular to the other, resolution is direction-dependent. In CT, where the part rotates through every orientation, that asymmetry smears fine features and reduces contrast on small defects.
The HP/15 reshapes the spot. Through revised electron optics and target design, it is more symmetric and more compact, with the wings removed. The improvement holds not just on the central ray but across the emission angle, which matters because the detector views the spot at an angle that changes across the field.
Homogeneous X/Y resolution
A symmetric spot means an edge is rendered with the same sharpness whatever its orientation. For 2D radiography that means crisper, more consistent images. For CT it means cleaner reconstructions, better small-defect visibility, and fewer orientation-dependent artifacts.
Focal spot shape HP/11
Focal spot shape HP/15
A wider beam, and what it buys you
A bigger usable field is not just convenience. It changes the geometry you can build and the speed you can run. The HP/15’s 15° target and anode assembly open the usable beam to 50° radial × 40° axial, against 40° × 30° for the HP/11, roughly 70% more usable area at the same distance. Just as important, the spot stays clean and small across that wider angle, so the extra coverage is genuinely usable, not just brighter in the middle.
More dose, more speed
A larger field lets you move the detector closer to the source for a given coverage. Dose at the detector scales with the inverse square of the distance, so closing that gap delivers markedly more dose, which you can spend on faster acquisition at the same resolution, or on higher resolution at the same speed.
No more tilting
X-rays are generated just beneath the target surface and must pass through the target material before leaving the tube. Toward the anode side, they travel through more material and are more strongly attenuated. This dose reduction is known as the heel effect.
A 15° target angle reduces attenuation and moves the significant dose falloff toward the edge of the usable field. HP/11 users can compensate by tilting the tube approximately 4–5° toward the cathode. However, this changes the angle at which the detector views the spot, stretching it in the length direction by more than a third. The HP/15 is designed for 15° from the outset, providing more uniform dose and a small focal spot without this trade-off.
Two spots - one insurance policy
The spot that used to sit idle now keeps the line running. Instead of a large spot that sits idle, the HP/15 carries two nearly identical small focal spots, thermally separated on the target. The second is effectively a built-in spare. If the first degrades, you switch to the second and keep inspecting rather than stopping the line for an emergency tube change.
Plan service, don’t fight fires
Used the same way, the second spot has a similar lifetime to the first, so replacement can be scheduled into a maintenance window instead of striking mid-production. That also means less local spare inventory to finance and store.
From specification to application - see the difference with HP/15
Parameters: 225 kV, 1.5 mA, 10 f, M3.96, FOD 450.
Measured in the lab, visible in the image
Every claim here is backed by focal-spot measurements following the ASTM E1165-20 user method, and by side-by-side images under identical conditions.
Focal-spot geometry
Measured across angle, not only on the central ray, the HP/15 holds a smaller, more symmetric spot, confirming the cleaner shape and wider usable beam.
CT image quality
On identical scans the HP/15 delivers sharper, more homogeneous reconstructions with better defect visibility and less focal-spot distortion.
Turbine-blade comparison
Same technique, same parameters: the HP/15 shows sharper Y-direction edges and more uniform resolution than the HP/11 - including the HP/11 tilted by 4°.
Clearly defined focal spots
Specifications now follow the ASTM standard, providing a focal spot size value that reflects achievable system performance.
The HP/11 is here to stay
It remains in the Comet portfolio and remains the right tube for established film and lower-magnification workflows. The HP/15 answers what has changed since then: digital detectors, in-line throughput, and CT.
Specifications of the HP/11 and HP/15
Feature | MXR-225HP/11 | MXR-225HP/15/04-04 | What this means for you |
| Target Angle | 11° | 15° | Root cause of gains below |
| Focal spots (ASTM E1165-20) | 0.63 mm / 1.0 mm | 0.4 mm / 0.4 mm | Smaller defects detected |
| Small focal-spot shape | Asymmetric, with wings | Symmetric, compact, no wings | Sharper edges, no wing blur |
| X/Y resolution homogeneity | Direction-dependent | Homogeneous | Same resolution in every direction |
| Usable beam coverage | 40° × 30° | 50° × 40° | Detector closer, faster scans, smaller footprint |
| Dose homogeneity | Typically requires ~4-5° tilt | By design, no tilt needed | Simpler integration, no tilt fixture |
| Small focal spots for redundancy | One | Two, thermally separated | Second spot keeps the line running |
| Max. continuous power | 800 W | 850 W | More dose, shorter exposure |
A note on standards
Many users know the MXR-225HP/11 as a 0.4 mm tube. That value comes from EN 12543-2:2008, evaluated at a 30 % threshold, which does not include the wings of the focal spot. Since the 2021 revision, EN 12543-2 uses the Integrated Line Profile method, the same method as ASTM E1165-20. This method includes the wings, because a real radiograph includes them too. Measured this way, the same focal spot is 0.63 mm. All values in this document follow ASTM E1165-20, for both tubes.
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