Custom work is a specification exercise
Ordering a custom optical element is a specification exercise first and a purchase second. The element does not exist as a fixed catalogue entry, so there is no table to pick from and no model number to quote. What exists is a requirement, stated by the buyer, checked by the supplier, and confirmed before ordering. That sequence, requirement, check, confirmation, is the whole custom process, and every step in it exists to prevent the same failure: an element made to a specification that was never clearly stated. This note walks through the process step by step, using the same discipline that appears on the custom ordering process page and the custom optical filters page.
Step one: describe the optical job
Describe what the element must do with light, in plain terms, before naming any parameter. Must it pass a band and reject its neighbours? Must it cut off one side of a spectrum? Must it split or combine beams? Must it attenuate light evenly? Must it focus light, or turn a beam by a defined angle? That job description decides which category the element belongs to, and it decides which parameters matter. A job described as pass a narrow band leads to different parameters than a job described as attenuate evenly, and a job described as focus light leads to different parameters again. Buyers who skip the job description and jump to parameters often state parameters for the wrong job, and the error only appears when the element is tested.
Step two: list the parameters that decide fit
For filters, the parameters are centre wavelength or wavelength range, bandwidth or pass band behaviour, cut-off depth where it applies, size and shape, and substrate material. For fluorescence work, add the dye or probe name from the documented list, and the excitation and emission requirement. For neutral density work, add the ND value and the wavelength range. For prisms and lenses, add the model description, size, and material, together with the focal behaviour or working distances where they matter. List every parameter that decides fit, even if you are unsure of its value: an unsure value stated as unsure can be discussed, while a missing parameter cannot be checked at all. State the wavelength region every parameter applies to, because a parameter without a region is ambiguous.
Step three: describe the system
Describe the system the element will sit in: the instrument type, the optical path, the mounting approach, and the other elements it must work with. A filter for a fluorescence instrument needs a different description than a filter for a measuring instrument, even if both mention similar wavelengths, because the surrounding optics, the detector, and the light source differ. A prism for a beam-turning assembly needs its angle behaviour and mounting described, not just its name. A lens for an imaging assembly needs its geometry described, not just its shape name. System description is what turns a list of parameters into a requirement that can be checked in context, rather than a list that looks complete but fits no real system.
Step four: state quantity basis and delivery basis
State the quantity basis and the delivery basis you need confirmed, as part of the same inquiry, not as an afterthought. Custom work is often ordered in quantities that differ from catalogue work, and delivery depends on the specification's complexity, so both items need confirmation alongside the specification. No quantity figure and no delivery figure is published for custom work on this site, which is why both must be stated and confirmed in the inquiry. An inquiry that states a perfect specification but omits quantity basis and delivery basis is still incomplete, and it will generate a second round of questions before it can proceed.
Step five: review the confirmation
Review the confirmation against the requirement you stated, item by item, before proceeding to ordering. Check the wavelength region, the band or edge behaviour, the size, the material, and the set composition where a set is involved. Check that the confirmation covers the specification you stated, not a similar specification. A value confirmed for your custom element is your confirmed value: it does not become a new published specification for the catalogue, and it should not be quoted to others as if it were. That boundary protects the next buyer as much as it protects you, because it keeps the catalogue honest about what is documented and what was confirmed for one order only. Equipment names listed by the company, including Optorun OTFC 1300 and Leybold Syrus 1350 coaters and Cary 5000 and Cary 7000 spectrophotometers, are equipment names only, and no photograph on this site is presented as a photograph of custom production. Please confirm the specification, quantity basis, and delivery basis in your inquiry before ordering.
Common custom ordering mistakes
The first common custom mistake is stating a product name instead of a requirement. A name that meant one thing in a previous order may mean something different in a new context, and a supplier who works from a name alone must guess which meaning applies. State the optical job and the parameters, and let the name follow as a label, not as the specification. The second common mistake is stating parameters without a wavelength region. A bandwidth, a cut-off depth, or an ND value without a region is ambiguous, because the same value means different things in different regions. Always attach the region. The third common mistake is omitting the system context. An element that fits one instrument may not fit another with the same nominal parameters, because mounting, geometry, and surrounding optics differ. Describe the system, even briefly, and the requirement becomes checkable in context.
The fourth common mistake is treating confirmation as a formality. Confirmation is the point at which the supplier states what will be made, and the buyer checks it against what was asked for. Skipping that check, or checking only the headline value while ignoring size, material, or set composition, defeats the purpose of the custom process. Review every confirmed item, not just the first one, and query any item that differs from the requirement before ordering. The fifth common mistake is ordering a custom element for a prototype quantity and assuming the same specification will automatically suit production quantities. Prototype and production quantities may share a specification, but quantity basis and delivery basis still need separate confirmation, because they affect how the order is handled. State both, for the quantity you actually need, in the same inquiry.
Keep the written requirement with the order record, so that any later question about what was agreed can be answered from the requirement itself rather than from memory.