155mm Working Distance Zoom Lens: Setups for 60, 30 and 15 mm FOV

155 mm is not a property of the 12.5X zoom body — it is one published step in its auxiliary-objective table, and the most useful one.

Why 155 mm Working Distance Keeps Appearing in Inspection Specs

Most zoom lens requests arrive with a field of view attached. A smaller group arrives with a distance: the fixture exists, the light ring is mounted, and the gap between lens and part is already fixed at roughly 150 mm to 160 mm.

The 12.5X family answers that with an accessory, not a new body. Its auxiliary-objective table lists seven steps: 297 mm at 0.25X, 120 mm at 0.3X, 155 mm at 0.5X, 93 mm at 0.75X, 77.4 ± 2 mm with no objective at all, 48 mm at 1.5X and 34.5 mm at 2X.

155 mm gets specified most because it is the widest-coverage step that still leaves real clearance: one objective spans a 60.7 mm field down to 1.2 mm with nothing but an adapter change, and the standoff clears a ring light and a safety gap.

The Combination That Produces 155 mm: 12.5X Body + 0.5X Auxiliary Objective

Two parts make the number: a 12.5X continuous zoom body — PMS-LZL-12101, LZL-12100D15 or LZL-12102-M12, published 0.58X–7.5X, 12.5:1, 2/3" image circle — and the 0.5X auxiliary objective (SKU 75205) on the front.

The objective is the front optic, which is why it owns the distance: it refracts the bundle so the object plane sits 155 mm ahead instead of 77.4 ± 2 mm.

Three lines follow, and all three get misread in quotations and datasheets:

• Distance belongs to the objective. 155 mm holds while the zoom ring turns from 0.58X to 7.5X.
• The bare body is a different number. Without an objective it is specified at 77.4 ± 2 mm. Both figures are correct — different front optics.
• The adapter never touches it. A TV tube sits downstream of the object plane: magnification and field of view change, standoff does not.

For the optics rather than the rule, see what an auxiliary lens actually does.

Effective Magnification at 155 mm — and What You Cannot Change

Effective magnification is base zoom × objective factor × TV factor. At 155 mm the objective factor is locked at 0.5X, so two variables remain: zoom position and the adapter behind the body.

With a 1X TV tube the range runs 0.58 × 0.5 = 0.29X to 7.5 × 0.5 = 3.75X; a 2X adapter cancels the objective and returns 0.58X–7.5X. Those are calculated, not measured, and the magnification and FOV calculator reproduces them.

Three things stay fixed:

• Clearance. 155 mm holds for as long as the 0.5X objective is fitted.
• The zoom ratio. Every tier keeps the body's 12.5:1 span; the rounded table values approximate it.
• The 2/3" ceiling. A larger sensor vignettes the corners instead of widening the field.

What changes is coverage: one adapter swap moves the field of view by a factor of two.

Three FOV Tiers at 155 mm: 60 mm, 30 mm and 15 mm

One objective, three adapters, three coverage tiers. Every row holds the distance at 155 mm and changes only what happens behind the body.

Table 1 — FOV calculated as sensor dimension ÷ effective magnification on a 2/3" sensor (8.8 × 6.6 mm). 155 mm is a published working distance; effective magnification is calculated from base zoom × 0.5X objective × TV factor.

The ~15 mm row deserves a second look. The 0.5X in front and 2X behind cancel out, so magnification returns to the published 0.58X–7.5X and the field matches the bare body at 77.4 mm — the same coverage with a calculated 77.6 mm more clearance.

Pick rows by largest feature: a module face takes the 60 mm row, a 30 mm part takes the middle, an edge or seal line takes the 15 mm row.

What Each Tier Costs in Resolution and Depth of Field

Published resolution for the 12.5X body is 13 µm at 0.58X, improving to 3.05 µm from 4.5X — bare-body figures. Fit the 0.5X objective and one detector pixel covers approximately twice the object-side length at the same zoom, calculated from the magnification ratio alone. Recovering bare-body sampling means zooming higher, which costs field of view. The ~15 mm tier is the exception: 0.5X × 2X restores bare-body magnification, so published figures apply unchanged.

Brightness follows the same trend — the same light spreads over more pixels — so check illumination per tier. Depth of field is the honest gap: POMEAS does not publish DOF for these combinations, and the body figure does not transfer, because a front objective changes magnification and effective aperture. See working distance versus depth of field and a real case on improving DOF.

Table 2 — Sampling and brightness comparisons calculated from the magnification ratio, relative to the bare 12.5X body at the same zoom position. DOF for these combinations is not published.

155 mm vs 93 mm vs 297 mm: Choosing the Right Tier

The 155 mm step is the medium working distance tier — the middle child: 297 mm with a 0.25X objective above it, 93 mm with a 0.75X objective below. Compared at one adapter, the trade-off needs no arithmetic.

Table 3 — Calculated as base zoom × objective factor × 1X TV tube on a 2/3" sensor. WD values are published.

Now the part usually missed: two different steps can deliver an identical field of view, because objective and TV factors multiply.

Table 4 — Same calculated magnification and FOV; the two working distances are 142 mm apart (calculated: 297 − 155).

Identical magnification and field, different standoff — so field of view cannot pick a distance on its own. Take the WD from clearance and the sampling from feature size, then let the adapter fix coverage. DOF is unpublished for both combinations. If your standoff is nearer 300 mm, the 300 mm working distance route covers the 0.25X step and its corners.

Which Sensor Fits Behind the 12.5X Body

The 12.5X body is specified up to 2/3". Treat that as a field-of-view limit: field of view is sensor width ÷ magnification, so a bigger sensor looks like it widens the field, but only if the image circle covers it.

Table 5 — HFOV calculated from the 0.5X-objective + 0.5X-TV configuration (0.145X–1.875X). Active areas are the sensor sizes POMEAS specifies.

The 1" row is the trap: the arithmetic looks attractive until the corners arrive black. The sensor and image circle matching guide shows how to check coverage against the image circle, which matters more here than pixel count.

Manual or Motorized at 155 mm

At 155 mm the manual-versus-motorized question is not about distance: the standoff is identical on both. It is about how often the zoom position changes.

Manual suits one continuous recipe — set the ring at commissioning, let the adapter do the tier switching. The detented variant (LZL-12100D15) adds repeatable click positions for returning to a known magnification. Motorized earns its place when the configuration switches itself: one recipe reading a module face at 0.29X, then 3.75X for a seal line.

Two details decide it: wiring (controller, link, PLC recipe) and repeatability (recalled positions versus a scale read by eye). The manual versus motorized guide covers the rest; compare the coaxial LZL-12101 body with the manual 0.58X–7.5X version.

Where 155 mm Configurations Are Used

Three process patterns account for most 155 mm requests.

Clamped assemblies with fixture walls. A housing sits in a nest with walls on two sides and a clamp on top. The ring light must clear the clamp, and one exposure must cover the top face: 155 mm with a 0.5X adapter gives a calculated 60 mm field, then zooms for a gasket line.

Populated boards in a conveyor nest. Tooling locates the board, so the lens cannot come close. A calculated 30 mm field covers a connector block; travel from 0.29X to 3.75X covers block and joints from one station.

Small parts in a holder. Ferrules, lens barrels and cannula tips face the lens with no room for a short standoff optic. The 15 mm tier gives a calculated 1.2 mm field at the tight end for edge and burr checks.

If the part is fixed and the field is the unknown, the reverse route is selecting backwards from a 30 mm field of view. If distance, FOV or camera is already fixed, start from the zoom lens configuration guide.

Spec, Order and Verify: A 155 mm Checklist

The usual failure is not optical but a line item: an objective without the right adapter, or a body ordered at 77.4 mm when the drawing says 155 mm.

• Confirm the distance reads 155 mm. A 150 mm requirement is a fixture change, not a lens option.
• Name the objective: 0.5X, SKU 75205 — the only step at 155 mm.
• Name the adapter: 0.5X (75105), 1X (75110 / 75110G) or 2X (75120), matched to your tier.
• Cap the sensor at 2/3" and reject any 1" field-of-view figure for this body.
• Ask about DOF in writing; it is not published for these combinations.
• Ask about the WD tolerance: the bare body is 77.4 ± 2 mm, the 155 mm row carries none.
• Check illumination at the tight end rather than assuming it.

Then verify on a sample: put a scale at the real part height, capture at both ends of the zoom travel, measure. A calculated 30.3 mm that matches your own measurement confirms the configuration — a single 10–4 mm FOV selection shows how that loop runs.

FAQ: 155 mm Working Distance Questions

What exact configuration gives 155 mm working distance?

A 12.5X continuous zoom body with the 0.5X auxiliary objective (SKU 75205) on the front. The 155 mm figure is published in the 12.5X auxiliary-objective table, and it holds at every zoom position from 0.58X to 7.5X.

How much field of view do I get at 155 mm working distance?

Three tiers, all calculated on a 2/3" sensor: a 0.5X TV tube gives 60.7 × 45.5 mm down to 4.7 × 3.5 mm at 0.145X–1.875X, a 1X TV tube gives 30.3 × 22.8 mm down to 2.3 × 1.8 mm at 0.29X–3.75X, and a 2X TV tube gives 15.2 × 11.4 mm down to 1.2 × 0.9 mm at 0.58X–7.5X.

Does changing the zoom position or the TV tube change the 155 mm working distance?

No. On this route the working distance is set by the front auxiliary objective, so it stays at 155 mm from 0.58X to 7.5X and through any adapter change. The zoom ring and the TV tube change magnification and field of view only.

Which auxiliary objective gives exactly 155 mm, and what are the neighbours?

The 0.5X objective is the only step published at 155 mm. The nearest steps are 0.3X at 120 mm and 0.75X at 93 mm, with 0.25X at 297 mm beyond that, so a meaningful change in standoff moves you to a different objective.

Is 155 mm enough clearance for a fixture or a light ring?

It is enough for most fixture and light-ring stacks, but treat it as a budget: add the fixture wall, the light ring and a safety gap, then compare the total with 155 mm. If the total is larger, the next step out is 297 mm with the 0.25X objective.

Should I choose 155 mm, 93 mm or 297 mm?

Choose by clearance first. The 93 mm step with a 0.75X objective gives the finest object-side sampling at a 1X TV tube, 155 mm balances clearance and sampling, and 297 mm buys the most standoff at the cost of sampling. Compare calculated field of view second.