Shortpass vs UV/IR-cut - what's the difference for cameras?
Choosing the right optical filter is key for anyone using cameras in photography, machine vision, or scientific imaging. Two common filters—shortpass and UV/IR-cut—look similar but perform very different jobs. Here is a clear, side-by-side breakdown to help you pick the best filter for your camera application.
Shortpass vs UV/IR-cut: The Quick Camera-Focused Difference
Shortpass filter (SP):
Lets shorter wavelengths through, blocks longer ones. For example, a 650 nm shortpass passes UV, blue, green, and yellow, but blocks deep red and all near-IR. Use it to keep only the short side of the spectrum, ideal for blue LED lighting or when you want to reject longer wavelengths that wash out image contrast.
UV/IR-cut (visible-band or hot-mirror filter):
Blocks both ultraviolet (<400 nm) and infrared (>700 nm), letting in only visible wavelengths (~400–700 nm). This gives a visible-only pass that makes colors and focus true-to-life, because most camera lenses and sensors are not corrected for UV or IR. Commonly used in color cameras and the day mode of day/night security cams.
| Feature | Shortpass Filter (SP) | UV/IR-cut Filter |
|---|---|---|
| Color Fidelity | Skews colors to the blue/green side if you cut above 650 nm. Reds are muted. Great for setups with short-wavelength (blue/green) light. | Preserves normal color balance under white light by removing UV and IR that sensors 'see' but humans don't. |
| Focus & Sharpness | If UV is passed, some optics and sensors can't focus it well—possible haze or blur unless your optics/illumination avoids UV. | Improves sharpness by blocking light outside the visible band, reducing chromatic/focus errors the lens wasn't designed for. |
| Illumination Fit | Match to lighting cutoff. Example: With blue LEDs, a 500–550 nm SP blocks longer ambient/IR light and boosts contrast. | Best for full-spectrum (white) light when you want true-to-eye imaging. Most color cameras include one by default. |
| Applications | Machine vision, fluorescence, scientific setups using specific short-wavelength light. | General color imaging, security cams, astrophotography for most accurate color rendering. |
Real-World Examples
Shortpass: Say you're using blue LED lighting for inspection. You select a shortpass filter with a cutoff near your light's peak, maybe 500–550 nm, to get only the strong blue and block longer ambient/IR. This sharpens contrast and eliminates haze.
UV/IR-cut: Want your camera to record images as close to what your eye sees as possible? Use a UV/IR-cut to block light your camera can detect but you can't see, to deliver natural color and crispness. Many color cameras have a built-in version, sometimes removable for IR night imaging.
Mechanics & Tips- Both filter types come as dichroic (interference) coatings (angle-sensitive) or absorptive glass (less angle-sensitive but lower blocking).
- Hot-mirror UV/IR-cuts reflect IR away to reduce sensor heating—useful in projection or high-brightness systems.
- Day/night security cameras flip the UV/IR-cut in for color daytime imaging, and out for nighttime IR sensitivity.
- Always match the filter to your lighting cutoff. For shortpass, pick a cutoff just past your LED or source peak. For color imaging under white light, default to UV/IR-cut for the most accurate results.
- Angle of incidence matters (see next section); avoid tilting dichroic filters steeply unless specs allow it.
- Don't double-stack UV/IR-cut filters unless needed, to avoid extra reflections or ghosting. Always face the coated side toward the light.
- The edge of a dichroic filter shifts 'bluer' (shorter wavelength) at higher angles of incidence.
- If you can't avoid high angles, ask for a custom coating to compensate for blue shift or consider absorptive glass.
- For most bandpass filters, use close to 0° AOI for predictable results (tolerance is usually ±5°).
- Don't double-stack built-in plus external UV/IR-cut filters unless there's a specific reason.
- Shortpass: Keeps the short side of the spectrum. Tune it to your illumination (may pass UV, may not preserve color).
- UV/IR-cut: Keeps only the visible (best for natural color imaging and for general color cameras).
If you are unsure which filter or wavelength cutoff is best for your lens, camera, or light source, feel free to share your setup for personalized recommendations.
