Pay attention to when using the proper focal length, you can get clear image of the sun.

About a ND filter

ND filter, also known as the grey density mirror, attenuation mirror.Its effect is weaken light, and won't impact to the color of the original object, can reproduce the contrast of scenery.In astronomical photography, main purpose to use ND filter is to prevent excessive exposure, such as shooting the moon and the sun, can be shown the effect of the captured is invisible to the naked eye.ND reduction were roughly ND0.3, ND0.6, ND0.9, ND3.0 models, such as digital represents its obscuration degree respectively, the greater the number, the stronger the light reduction ability.

ND filter commonly used categories:
ND - 2: we can cut 1 aperture and 50% of the amount of light;
ND - 4: can cut 2 levels of aperture and 75% the amount of light;
ND - 8: can cut 3 aperture and 87.5% of the amount of light;
ND - 400: the amount of light can cut 9 aperture, suitable for long days time exposure and photograph the sun.

ND Filter Priciple Schematic Diagram：

Different wavelengths of light through the ND filter, ND filters can reflect or absorb was not the light transmission parts, with evenly reduce the spectral transmittance of a part of, to avoid light damage to the camera sensor or other optical.