What is a UV/IR Cut Filter
Camera sensors are typically sensitive to a broad spectrum of light, including ultraviolet (UV) and infrared (IR) wavelengths. This can result in color distortions and a decrease in image sharpness when taking standard photos. To address this, UV/IR cut filters are used to block these unwanted wavelengths, allowing only visible light to reach the sensor.
For photographers who want to explore both UV and IR photography while still having the capability to capture regular images, UV/IR cut filters are essential. They enable a smooth transition between specialized UV/IR shooting and conventional photography, preserving image quality across different types of shots. By using a UV/IR cut filter, you can enjoy the full spectrum capabilities of your camera while ensuring that everyday images remain sharp and color-accurate.
The IRC 700nm filter
Tangsinuo's BCF700 filter is an Infrared Cut 700nm filter, which they sell as a cheap option of a Baader 700nm filter. With its sharp cutoff at 400nm and 700nm, is designed to block UV and IR light while allowing visible light to pass through. This kind of sharp cutoff is effective in providing a clear boundary for the transmitted wavelengths. However, this design may not be optimal for addressing certain color balance issues, particularly the red leakage that can occur with many camera sensors.
BCF700nm Test and Sample Images
A filter test was conducted using a still life scene that included a color chart and a gray card for accurate white balance (WB). The setup featured a plant with green leaves to check for any IR leakage on the vegetation. Initially, the WB was set to Auto, and then a custom WB was performed on the gray card during post-processing. The images below illustrate the color deviation when compared to those taken with a non-converted camera.
Key Points about Sharp Cutoff Filters:
Sharp Cutoff Characteristics:
A filter with sharp cutoffs will abruptly stop transmitting light outside its specified range. This can be effective for blocking unwanted UV or IR light, but it might not handle color balance issues as well as filters with more gradual transitions.
Red Leakage and Sensor Sensitivity:
Camera sensors, especially those with silicon-based detectors, are often more sensitive to red wavelengths. Sharp cutoffs might not adequately manage the red leakage, potentially resulting in color casts or dominance in your images.
Gradual Transition Filters:
Many modern UV/IR cut filters use a more gradual transition to address the specific needs of camera sensors. These filters, like those found in heat-absorbing or blue-turquoise glasses, provide a smoother transition between transmitted and blocked wavelengths. This can help reduce color casts and maintain a more balanced color reproduction.
Absorptive vs. Dichroic Filters:
Absorptive filters, which absorb unwanted wavelengths rather than reflecting them, tend to offer smoother filtering compared to dichroic filters. Dichroic filters reflect unwanted wavelengths and can create sharp cutoffs, while absorptive filters typically provide a more gradual filtering effect, which can be beneficial for managing color balance and reducing red dominance.
Aftermarket Solutions:
Many aftermarket UV/IR cut filters are designed with these smoother transitions in mind, addressing common issues like red leakage and color casts. These filters are often optimized for better image clarity and color accuracy, making them a good option if you are experiencing issues with color balance using standard filters.
