I ache, therefore I am
Quote:Interesting idea but photographic filters are rarely anywhere near 1/4 wave RMS & when placed at the objective end of the scope will usually cause a significant loss of resolution.
Turbo film does not need to be "flat" to work well but should definitely not be under tension.
Quote:How flat is 1/4 wave? The Tiffen fiter is described as being opticallhy pure Water White glass which is ground flat to a tolerance of 1/10,000th of an inch.
Quote:What about Hoya Clear Filters? They are used as a filter replacement by those who modify their DSLR for full spectrum sensitivity.
Quote:For the image quality to be maintained, shouldn't all lens elements and filter glass be at least 1/4 wave or better all the way down to the sensor cover glass?
Bob diagonally parked in a parallel universe...
Quote:I would suggest using either a Baader Red CCD filter or a Baader IR/UV filter - these are specified as being polished to 1/4 wave: http://www.alpineastro.com/filters/filters.htm The only problem with going that route is the fact that the filters are only 50.8mm unmounted. That's barely enough room to fit in the cell window.Astrodon filters are also specified as being 1/4 wave on fused silica substrate... again I'd go with the Red CCD or IR/UV: http://www.astrodon.com/products/filters/e-series/