Optolong Clear Focusing Filter 1.25″
With a 98.5% transmission of the visible spectrum region of 420-680nm, the Optolong Clear Focusing Filter can be used to easily focus your photographic subject before imaging.
This is especially helpful when doing astrophotography through narrowband filters, since the subject is often so dim that focusing is difficult. The Optolong Clear Filter also makes a good dust shield.
The Optolong 1.25” Clear Focusing Filter is made Schott glass that has been multi-coated with ion-assisted deposition technology to ensure scratch resistance and stability on the central wavelength, or CWL. The filter cell is made of lightweight, strong metal and is CNC machined, sand-blasted, black anodized, and then laser engraved. The result is a super thin filter cell that will produce a clear aperture of 26mm.
Quality Filter Materials:
- Schott B260 substrate material from Germany, 2.0mm thick
- CNC machined and black anodized aero-metal filter cell that is ultra-thin to provide largest clear aperture; Laser-engraved to prevent fading
- Multiple layers of anti-reflection non-cementing coatings applied via electron-beam gun evaporation with Ion-assisted deposition
Optolong Filter Manufacturing Processes and Parameters
- Filter substrate is fine-optically polished to 1/4 wave and <30 parallelism over both surfaces
- Surface quality, according to MIL-O-13830, is 60/40
- 98.5% transmission at visible spectral range 420 – 680nm
- High value transmission of pass-band and optical density of off-band is assured through Optolong’s planetary rotation system, a homogenous and precise coating procedure
- Thin metal cells have a clear aperture of 26mm for 1.25” filters
- Each filter comes with a plastic case with high pressure EVA case lining