Material specifications: 100% high quality optical resinOptical properties: 0.6, 0.9, 1.2 optical density, 25% - 6,25% of light transmittance in the top part, 2F - 4F stops light reductionOptical density tolerance: +/- 1%Available dimensions:75x90mm, 84x100mm, 100x150mm, 150x170mmVISIBLE LIGHT SPECTRUMLIGH TRANSMITTANCEMEDIUM GRADUAL ND filters have various density throughout filter space (from dark to light with hard transition). It means that light incoming to camera is reducing gradually. This is very useful in situations where some of parts of the photography are overexposed (too much bright sky). MEDIUM Filter is perfect for non-straight horizonts. It is very good compromise between HARD and SOFT.MEDIUM GRADUAL ND filters are able to use with full or gradual filters in stacking mode.