VHX-Class Digital Microscope

The Category, Not the Brand

VHX is a product name used so widely that it has become a shorthand for a class of instrument: a motorised digital microscope with a zoom head, focus stacking and on-screen measurement, used for quality inspection rather than for laboratory work.

The characteristics below describe that class. They are not a specification of any particular model, and no POMEAS instrument is claimed to be equivalent to any specific product in it.

Focus Stacking and the Depth of Field It Buys

The defining capability of the class is that it builds a single image from several focal planes. A high-magnification objective has a shallow depth of field, so no single frame contains a rough or inclined surface entirely in focus. Stacking acquires frames at successive heights and combines the sharply focused region of each.

The result is an image whose apparent depth of field exceeds the objective's own, which is why these instruments can show a whole fracture surface or a deep groove in one view.

The limit is that each frame is acquired at a different moment. A moving part cannot be stacked reliably, so the technique assumes a static sample.

On-Screen Measurement and Its Calibration

Distance, angle, radius and area measurements are taken on the displayed image against a calibration established at the same magnification.

The accuracy of those measurements is bounded by the optics: object-space resolution, distortion across the field and the stability of the magnification. A calibration at the field centre does not automatically apply at the edge.

Across the POMEAS microscope units that publish them, object-space resolution spans 0.2 to 75 um and distortion is 0.06 %. Those two figures are what a measurement claim rests on.

Motorised Zoom and Its Working Distance

A motorised zoom changes magnification without a lens change, and on this class of instrument the working distance changes with it because the optics move.

Across the POMEAS microscope units working distance spans 22 to 55 mm. That range is modest because the illumination path occupies the same space, and it sets what can be presented under the lens.

The practical consequence is that a part with tall features may not fit under the high-magnification configuration at all, and the choice of presentation becomes part of the specification.

How to Judge Any Instrument in the Category

Ask for object-space resolution in micrometres, working distance, field of view at each magnification and the distortion figure. Those four describe the capability.

Ask how the focus stack handles sloped surfaces and how many frames it acquires, because the acquisition time determines whether the method is usable in a production cadence.

Ask how the calibration is verified and how often. An instrument whose calibration cannot be re-checked supports visual judgement, not controlled measurement.

Where the Category Fits and Where It Does Not

It fits where the feature is small, the surface is three-dimensional and the result has to be documented. Fracture surfaces, tool wear, weld cross-sections and micro-assembly inspection are its natural applications.

It does not fit where the field is large and the measurement is whole-part, because the field of view at high magnification is small and stitching introduces its own error. For those, a vision measuring machine is the correct instrument.

Deciding between the two is a question about field size and feature size, not about magnification.

Frequently asked questions

Is VHX a brand or a category?

It is a product name that has become shorthand for a class of motorised digital microscopes with zoom, focus stacking and on-screen measurement. The characteristics are shared across the category; they are not a specification of one model.

How does focus stacking extend depth of field?

It acquires frames at successive focal heights and keeps the sharply focused region of each. The combined image appears to have a depth of field larger than the objective provides. It requires a static sample.

Can I measure on the screen image?

Yes, against a calibration established at the same magnification. Accuracy is bounded by object-space resolution, distortion across the field and magnification stability, so a centre calibration does not automatically hold at the edge.

What is the working distance on this class of instrument?

Across the POMEAS microscope units it spans 22 to 55 mm. The range is modest because the illumination path occupies the same space in front of the part.

How many figures should I ask for?

Four: object-space resolution in micrometres, working distance, field of view at each magnification, and distortion. Together they describe capability without depending on how magnification is quoted.

When is a measuring machine better than a digital microscope?

When the field is large and the measurement is whole-part. A digital microscope is the right instrument when the feature is too small for a large-field system to resolve.