Product Name: ND2 - ND400 Adjustable Neutral Density Filter Lens Material: AGC Optical Glass (Professional Glass Material, Not Resin) Frame Material: Aviation Aluminum Frame Thickness: 6.6mm (Ultra - thin Version) Lens Pressure Spring: Screw - in Type Available Apertures: 37/40.5/43/46/49/52/55/58/62/67/72/77/82/86/95/105 Main Function: The adjustable ND filter is an entry - level and practical filter. Rotating the frame allows you to observe the cyclic change from bright to dark. It provides an adjustable ND value range (recommended ND2 - 400), which can meet the light reduction requirements under different light intensities, eliminating the need to prepare multiple fixed - level ND filters. In photography, ND filters can prevent overexposure and facilitate photography with large apertures, long exposures, and slow shutter speeds.
How to Fit Installation Method: 1. The filter is connected to the lens via threads. Align the filter with the lens interface, screw it clockwise into the front end of the lens, and tighten it. 2. Turning counterclockwise will loosen the filter, allowing you to unscrew it. Tips: 1. When using the adjustable ND filter, rotate the frame clockwise for adjustment to prevent the lens from loosening. 2. The frame is rotatable. When installing or removing the filter, screw it to the lower frame position (the metal ring with knurling that connects to the upper frame marked with English labels). 3. For long - exposure photography, the adjustable ND filter is suitable for low - light environments. Generally, avoid shooting in strong - light environments. For long exposures during the day, it is recommended to use a fixed - level ND1000 neutral density filter to adapt to complex environments.
Fourth Eye Professional High - Quality Filter 1. Understanding Adjustable ND ND is the abbreviation of "Neutral Density" in English. In Chinese, ND filters are also called neutral density filters, gray filters, etc. In terms of appearance, there are two types: circular screw - in type and rectangular insert type. In terms of light reduction methods, they are divided into fixed - value quantitative neutral density filters (such as ND8) and variable neutral density filters that can adjust the brightness of incoming light (such as the Fourth Eye adjustable ND2 - 400). 2. The Difference between ND and GND Filters Neutral gray filters are functionally divided into non - graduated and graduated types. Non - graduated ones are ND filters, and graduated ones are GND filters (graduated neutral density filters). Graduated neutral density filters are further divided into soft - graduated and hard - graduated types. 3. The Function of ND Filters The main purpose of using an ND filter is to prevent overexposure of photos. When the light is too bright, using an ND filter to reduce the light entering the lens allows for shooting with a slow shutter speed. For example, when shooting a waterfall with a long exposure time to show the blurred water flow effect under normal light conditions, an ND filter is needed. 4. Choosing Fourth Eye ND Filters Using Fourth Eye ND filters can fully unleash the potential of the lens. The effect of ND filters is difficult to adjust in post - processing with software like Photoshop. Therefore, instead of relying on post - processing, we should focus on using appropriate filters in the pre - shooting stage to improve the shooting quality. PS: There is a formula to easily calculate the exposure time after adding an ND filter. Assuming that the shutter speed for normal exposure without an ND filter is T, after adding the ND filter, under the same lighting conditions, aperture, and ISO settings, the shutter speed with the ND filter = T * x (x is the number marked on the ND filter). For example, for a photo with an original correct exposure time of 1/30 second, after adding an ND400 filter, the exposure time becomes approximately 13 seconds.
Customer must read 1. The frame of the adjustable neutral density filter is a combined frame. Rotating the frame can drive the lens to rotate relatively, achieving the effect of adjustable ND values. By rotating the frame, we can observe the change of the lens from bright to dark. 2. The adjustable neutral density filter uses the principle of stacking two CPL (Circular Polarizing Lenses) to achieve adjustability. The recommended usage range is ND2 - ND400. High - density levels such as ND1000 and ND2000 cannot be achieved. 3. When using the adjustable neutral density filter, first familiarize yourself with the scale range. Mount the filter on the lens and face the sky or a bright area. Rotate from the min position to the max position, and pay attention to the color changes in the viewfinder. When uneven light reduction first appears, note the scale at this position (the slow - shutter switching position). For the subsequent scale range, long exposure is required to eliminate the "butterfly shadow" and "X - shaped shadow". In the high - density range, a long exposure of more than 4 seconds is generally required to eliminate obvious uneven light reduction. Uneven light reduction is a moiré pattern, not a quality problem, and can be eliminated through sufficient long exposure. The Max position is the limit position. There is an obvious "X - shaped shadow" close to ND1000 and it cannot be used. The recommended usage range of the adjustable neutral density filter is ND2 - 400. 4. The adjustable ND filter is a practical neutral density filter. When used in combination with fixed - level ND1000 and ND2000 filters with high - density values, it can meet the long - exposure photography needs in complex environments and is worth having. #### Frequently Asked Questions When using the adjustable neutral density filter, familiarize yourself with the scale range. The operation and precautions are the same as those in the above usage instructions. In the high - density range, diagonal shadows can generally be eliminated with a long exposure of more than 4 seconds. The "X - shaped shadow" that appears at the MAX position is an unusable position and is a positioning point for the lens. #### FOURTH EYE Adjustable ND Parameter Description The adjustable ND (Adjustable Neutral Density Filter) is made by utilizing the superimposed light - adjusting performance of polarizing sheets. The Fourth Eye adjustable ND filter is made by combining polarizing sheets and glass lenses and assembling them on a rotatable metal frame to achieve the adjustable function. The scale of the adjustable ND filter is divided into MIN minimum position -> sudden - change position -> MAX maximum (critical) position. MAX maximum (critical) position: Due to the characteristics of the polarizing sheet, this position is an optical critical non - light - passing position, and a cross - grating optical path (cross - color difference) will be generated. It is the reference alignment position in production and is not recommended for actual photography. Sudden - change position: Generally, it is a scale limited by the effective light - adjusting angle of the polarizing sheet. It can be divided into 20 positions, 10 positions, or random positions without scales. For the Fourth Eye adjustable ND filter, we have two types: 20 - position and 10 - position. Among them, positions 1 to 14 (1 to 7 levels) are normal light - reduction positions, and positions after 15 (6 levels) are positions dedicated to slow - shutter shooting. When using the automatic mode for light reduction at the slow - shutter dedicated positions, fan - shaped polarized light will appear, affecting the image effect. In the M mode, due to the superposition of light exposure, this effect can be effectively eliminated. MIN minimum position: It is the position where the two polarizing sheets do not interact with each other, generally ND2. Optical Parameters Corresponding to ND Values: | ND Value | Visible Light Transmittance | | ---- | ---- | | ND2 | 45 - 50% | | ND4 | 25 - 26% | | ND8 | 11.5 - 13% | | ND16 | 6 - 6.25% | | ND32 | 3 - 3.125% | | ND64 | 1.4 - 1.56% | | ND128 | 0.78 - 1% | | ND256 | 0.3 - 0.4% | | ND400 | 0.2 - 0.28% | | ND800 | 0.12 - 0.13% | | ND1000 | 0.08 - 0.11% | | ND2000 | 0.03 - 0.06% |