Televue 4" f5 Comparison

All fine yet very similar, but improved, instruments over the years offered by Al Nagler at Televue; but can anyone provide a more comprehensive reference or offer a detailed comparison of imporvements, including glass types, if possible, for: Renaissance, Genesis, Genesis SDF, TV101, NP 101, NP 101 is ? Thanks.

Ron Rogers said:

....can anyone provide a reference or offer a detailed comparison of imporvements....... NP 101, NP 101 i ? Thanks.

I listened in when a person asked David Nagler "Why the i's?" at NEAF. His answer was that most of their customers for these scopes are imagers using ever bigger CCD chips. The "i's" correct a vignetting problem with the old scopes (NP-101) when imaging with large chips.

Per the TV website: "The NP101 (540mm, f/5.4, 4") maintains their optical specifications yet with redesigned 4-element optical systems. Larger rear lens groups absolutely minimize vignetting in formats up to 50mm diagonal. For these large chips an optional field corrector was developed so the corners of the newly brightened edges would virtually be as perfect as the center of the field."

George N

The original Genesis had a fluorite element in the rear doublet along with ordinary glasses; there was significant color. Supposedly the performance was something like an F30 achromat. Mine had noticeable red defocus that gave the first diffraction ring a red/orange appearance. My particlar sample had a small amount of spherical abberation and a touch of color wedge--I encountered someone elses at a star party that also suffered from about 1/4 wave spherical, but no color wedge.

My current NP-101 is flawless in all respects, color correction like a reflector, absolutely superb wavefront.

In between, the objective and corrector have incorporated various special dispersion (SD) elements, but so far as I know, Nagler does not reveal the design specifics. The original Renaissance achromatic petzval glasses were the subject of a patent disclosure and I raytraced the scope from there--it turned out to have an F11 front end and the corrector brought the final color correction to about F8. From there I guessed at the original Genesis and knowing the fluorite element was the third element, optimised a design that was probably "similar" to the Genesis and confirmed performance around F30ish. If anyone has the glasses of the NP-101, I would dearly love to know.