Plano-convex vs double-convex lenses

PHOSLENS catalogue guidance · Updated 15 October 2026

Choosing between a plano-convex and a double-convex lens starts with the light entering the lens and the required output. Use the geometry as a starting point, then compare the complete model specifications. A matching diameter and focal length alone do not establish suitability for your system.

A quick geometry comparison

Plano-convex (PCX)

One flat and one convex surface. A common starting geometry for monochromatic focusing or collimation where one side of the optical path is approximately collimated.

Double-convex (DCX or biconvex)

Two convex surfaces. Often considered for finite-conjugate imaging or relay arrangements with comparable object and image distances. Performance changes as the conjugate ratio changes.

For a PCX lens focusing a collimated beam, the curved surface normally faces the incoming collimated light. When collimating a diverging source, it normally faces the outgoing collimated side. Confirm orientation for the actual design rather than applying “curved side toward the source” to every arrangement.

Describe the optical task before choosing a model

Write down whether you are focusing a beam, collimating a source or relaying an image. State the object and image distances, or identify the side that is collimated. For an imaging inquiry, include the required magnification and field of view. This lets the discussion start from the optical task instead of a shape label.

Browse the published plano-convex lens series and double-convex lens series, then retain the exact candidate model names. Use the lens specification finder to narrow available catalogue records; open each result to review its full series and model table.

What to check in the catalogue

1. Wavelength and material. Record the operating wavelength or band and the exact listed glass grade. If transmission information is missing for your conditions, include that question in the inquiry.
2. Coating. Check the stated coating type and wavelength range for the individual model. Include the intended incidence conditions and any required reflectance or transmission criterion.
3. Aperture and mounting. State the beam size or required usable aperture, mechanical envelope and mounting constraints. Ask for confirmation where only the outside dimensions are published.
4. Focal and mechanical distances. Distinguish effective focal length from back focal length: EFL is referenced to a principal plane; BFL is referenced to the last optical surface. Include available working space and the distance definition your design uses.
5. Acceptance criteria. Specify the tolerances and inspection records you need. Leave unpublished parameters as questions; do not fill them from a similar model.

The optical parameter guide explains catalogue terminology. Geometry advice does not establish spot size, image quality or laser damage suitability for a particular PHOSLENS model; those require model-specific information and system validation.

An example inquiry brief

Use a brief such as: “We need to focus a collimated beam. Operating wavelength: [value]; beam diameter: [value]; target focal distance: [value and definition]; mounting space: [value]; required quantity: [value]. Please review these candidate model names and confirm the specified material, coating and acceptance requirements.”

For a finite-distance imaging arrangement, replace the beam description with object distance, image distance, magnification and field requirements. Add a sketch if it clarifies the distances.

Move from selection to an inquiry

Add the candidate models and quantities to your quote list. Include the operating conditions in the request, following the optical inquiry checklist. If the catalogue does not cover your requirements, use Custom Requirements to start from a drawing, sample, specification or design brief. Commercial terms and project-specific requirements are confirmed in the quotation.

Technical reference and preparation

Geometry, orientation and EFL/BFL definitions were checked against Edmund Optics: Understanding Optical Lens Geometries. The inquiry checklist is adapted to the current PHOSLENS catalogue and quotation workflow. This guide was prepared with AI assistance and checked against the cited reference and current catalogue links.