Inside Focus

Inside Focus

Outside Focus

Outside Focus

Eyepiece: 6 mm Zeiss Abbe ortho EP (617x magnification)

“The design is the same as for refractor 80_1, except the longer focalratio. The colorcorrection is equal to modern douplet ED Apos. Due to the longer focallenght the colorcorrection is clearly better than in refractor_1. Except for one minor difference : on the both images on the left side (inside focus) you can see a very tiny brighter center , on the right side you see a tiny darker center. This comes from an ultrathin central zone in the lens, which could be easily smaller than 1/10 wavefront p.t.v. Such an lens would also test with around 99% strehl and could be called is called 99.99% perfect.”

Markus Ludes (APM-Telescopes)

”The above simulation was done with the green-channel of the most inside-focus image.

Using 1/6 wave undercorrected LSA and 1/10 wave overcorrected HSA the best simulation was found at 7.4 waves of inside focus. This simulation seems to be reasonable good for the outer three rings. The inner-structure is ill-defined in the original and therefore the simulation-quality is not very high. Although the center seems slightly brighter in the original image this is also present in the simulation without using a zone. Using the above LSA/HSA amounts a total wavefront error of 0.211 (1/5) PTV and 0.051 (1/20) RMS is expected.”

Cor Berrevoets