The 'Black Chrome' Screens
The Series IV 'Stiletto' Professional Edition and Deluxe Model incorporate very specialized laboratory-grade gratings to achieve high resolution focusing while minimizing loss of light from the source. The result is that the photographer is able to focus directly on much dimmer stars than with standard ronchi gratings. The ultra high resolution of the 'Black Chrome' screen also compensates for changes in depth of field at very low f/ratios guaranteeing perfect focus even for very fast refractors and CCD imagers with f/3.3 focal reducers. Our 300 lpi ronchi, Hybrid Knife-edge, and CrossHair screens follow identical manufacturing steps to guarantee interchangability. Screens are produced on the very same equipment used to photographically etch computer chips.
High resolution is accomplished by etching the ronchi and knife-edge patterns directly on photo-quality soda lime float glass that is .5mm thick. The ruling pattern itself is vacuum deposited Low Reflection Black Chrome with a minimum 3%-R at 600 nm light. This computerized chemical process results in extremely crisp bar edges and bars that appear darker and more highly visible when focusing. The ronchi ruling itself is 300 lines per inch consisting of line/space widths of .00167" +/- 0.00010" . The knife-edge pattern is a perfect semi-circle. All screens measure 15mm in diameter.
The 'Black Chrome' screens ares truly a state-of-the-art components and the heart of the Series IV Professional Edition. They are well worth the small additional investment for those serious about astrophotography.
"I finally had a few clear nights here for some imaging, so I went on a tear and got quite a few nice images. It was easy to focus with the Stiletto IV and the new screen, even at 3.3. I tested the Stiletto against diffraction spikes and are far as I can tell, you calibrated it perfectly! " - Rob Bensko ( MX7 )
