The Orion 72mm Skylight Filter offers protection for the front glass element of your lens.
Simply screw it onto the filter thread of your lens (must be a 72mm thread) and it acts as a 'first defence' for your lens glass. Repairs or replacement of lens glass can be extremely costly. Replacing a scratched or broken filter is so much cheaper.
According to the website www dot neocamera dot com, the following is a list of some popular lenses that take a 72mm filter.
Canon EF 135mm F/2L USM
Canon EF 180mm F/3.5L Macro USM
Canon EF 200mm F/2.8L II USM
Canon EF 20mm F/2.8 USM
Canon EF 28-135mm F/3.5-5.6 IS USM
Canon EF 35mm F/1.4L USM
Canon EF 35mm F/1.4L USM II
Canon EF 50mm F/1.2L USM
Canon EF 85mm F/1.2L II USM
Canon EF-S 15-85mm F/3.5-5.6 IS USM
Canon EF-S 18-200mm F/3.5-5.6 IS
Canon TS-E 45mm F/2.8
Fuji Fujinon GF120 F/4R LM OIS WR Macro
Fuji Fujinon XF10-24mm F/4R OIS
Fuji Fujinon XF50-140mm F/2.8R LM OIS WR
Nikkor 1 10-100mm F/4.5-5.6 PD-Zoom VR
Nikkor AF 105mm F/2D DC
Nikkor AF 135mm F/2D DC
Nikkor AF 180mm F/2.8D IF-ED
Nikkor AF 24-85mm F/2.8-4D IF
Nikkor AF-S 24-120mm F/3.5-5.6G IF-ED VR
Nikkor AF-S 24-85mm F/3.5-4.5G ED VR
Nikkor AF-S 24mm F/1.8G ED
Nikkor AF-S 58mm F/1.4G
Nikkor AF-S DX 16-80mm F/2.8-4E ED VR
Nikkor AF-S DX 18-200mm F/3.5-5.6G ED VR II
Panasonic Leica DG Vario-Elmar 100-400mm F/4-6.3 ASPH Power OIS
Pentax HD DA 16-85mm F/3.5-5.6 ED DC WR
Samyang 85mm F/1.4 IF MC Asph
Samyang 85mm F/1.4 IF MC Asph AE
Sigma 150mm F/2.8 EX DG OS HSM APO Macro
Sigma 150mm F2.8 EX APO DG HSM Macro
Sigma 17-70mm F2.8-4 DC Macro OS HSM
Sigma 17-70mm F2.8-4.5 DC Macro
Sigma 17-70mm F2.8-4.5 DC Macro HSM
Sigma 18-200mm F3.5-6.3 DC OS
Sigma 18-250mm F3.5-6.3 DC OS HSM
Sigma 18-50mm F2.8 EX DC Macro
Sigma 18-50mm F2.8 EX DC Macro HSM
Sigma A 18-35mm F/1.8 DC HSM
Sigma C 17-70mm F/2.8-4 DC Macro HSM
Sigma C 17-70mm F/2.8-4 DC Macro OS HSM
Sigma C 18-300mm F/3.5-6.3 DC Macro OS HSM
Sony Alpha FE 24-240mm F/3.5-6.3 OSS
Sony Alpha FE 70-300mm F/4.5-5.6G OSS
Sony Alpha SAL 135 F2.8
Sony Alpha SAL 16-50
Sony Carl Zeiss Distagon T* FE 35mm F/1.4ZA
Sony Carl Zeiss Planar T* 50mm F/1.4
Sony Carl Zeiss SAL 24mm F2.0 Z
Sony Carl Zeiss SAL 85mm F1.4 Z
Sony Carl Zeiss Vario-Tessar T* FE 16-35mm F/4 ZA OSS
Sony FE Planar T* 50mm F/1.4 ZA
Sony GM FE 100mm F/2.8 STF OSS
Sony NEX PZ 18-105mm F/4G OSS
Tamron Di SP AF 180mm F/3.5
Tamron Di II AF 18-270mm F/3.5-6.3 VC
Tamron Di II SP AF 17-50mm F/2.8 XR VC
Tokina AT-X 840 AF D
Zeiss Distagon T* 1.4/35
Zeiss Planar T* 1.4/85
Zuiko 11-22mm F/2.8-3.5 ED
Zuiko 12-100mm F/4 IS PRO
Zuiko 12-60mm F/2.8-4 SWD ED
Zuiko 40-150mm F/2.8 PRO ED
Zuiko 9-18mm F/4-5.6 ED