The spot pattern shows the performance of the lens (and C8 system) to be diffraction limited. The Daystar filter is modelled as a BK7 window of clear aperture 31.75mm and thickness 23mm, as specified in the Daystar QPE white paper. The optical prescription for the C8 Edge scope comes from the website of Vladimir Sacek, "Notes on Amateur Telescope Optics" ( ). It is a 4-element design comprising 40mm diameter achromatic doublets from Edmund Optics (-80mmf and 120mmf) and (eBay) (-120mmf). The first figure below shows a WinLens analysis of the telecentric lens. My first images taken with this system can be found here on the forum: The focal reducer's operating demagnification is simply determined by fixing the image distance to the camera to the required value. For a focal reducer, I use a simple system of two closely-spaced achromatic doublets of 300mm focal length each to achieve focal ratios at the camera of f24 to f36 (corresponding focal reductions of 0.43x to 0.29x). Consequently, I used 4.4x for an acceptable degree of vignetting which can be removed by flat-fielding. I have found that, after focal reduction to give my design goal of f25 to f35 at the camera, the final image becomes progressively more subject to vignetting (by the filter), the higher the telecentric magnification. Focal reduction after the H alpha filter would then be used. lar/FP.htm) show that it is not unreasonable to aim for focal ratios of around 50 (implying a magnification of 50/10.27= 4.9x for the C8). The calculations of Christian Vladrich (. I have analyzed designs up to 8x magnification. I also wanted to use as high a telecentric magnification as possible to fully optimize the operation of the Daystar filter. My design goals were to keep the lens train as short as possible and use off the shelf lenses, with a preference for achromatic doublets. The telecentric magnification is about 4.4 with a (design) field angle of 0.012 degrees. I thought I would add some information about the latest telecentric lens I've designed for use with a C8 Edge.
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