The Zerochromat???????????

Welllllllllll I have to say when I came across this scope in the latest issue of Astronomony Technology Today my curiosity was peaked. I went to their website to find out more about it. The site was not a wealth of information, but it did explain what is going on. So is this the next step in the evolution of the refractor or just a new twist on old ideas. I know folded refractors have been around for quite a while. What makes this scope so interesting to me is the simple design of the objective. Here we have an 8" color free refractor with all its benefits of unobstructed aperture without the nose weight of a triplet lens group in cell at about 2/3 the price. Collimation issues? I don't know. Maybe they are able to fix the mirrors in place and they never need to be adjusted. Some of the negatives I see is there doesn't seem to be much in the way of options. It looks like the diagonal is integral so dielectric upgrades may not be possible. The focuser may or may not be replaceable if it is lacking in smoothness or weight carrying ability. It appears to be a single speed. The light cone makes 3 passes through the tube like an SCT so tube currents come more into play, but the cool down time of the objective may make that a push. The overall weight is much less than a comparable APO triplet of equal size. The weight savings comes in making the color correction at the small end of the light cone. This probably won't appeal to many imagers as it is slow at f/12. It kinda makes me think of a MCT minus the central obstruction. So is getting rid of the c.o. worth about 3X the expense? That's certainly worthy of debate. So whatdayall think? Is this just an oddity to be relegated to the astronomy hall of obscurity or the perfect compromise between the high dollar APOs and the long focal length reflectors?

DanL

It's a twist on an old idea. Dialyte scopes are as old as the first achromat - going back 150+ years (invented by Plossl around 1850). They were first proposed as the answer to the problem of getting good flint material in large sizes. Back then one could obtain good crown glass, but in order to make an achromat, one needed an equal size flint glass of high quality. Problem was, nobody made a good high quality flint (even Alvan Clark used to complain bitterly about the junk flints that he had to work with). The Dialyte tried to solve this by sung a full aperture crown up front with a small aperture flint some distance down the tube. These scopes did sort of work, but fields were narrow because the design has inherent lateral color.

The modern dialyte has been updated using computer design software, so now one can do this using a number of carefully spaced small aperture lenses mounted at several places inside the tube. The front element is a simple inexpensive crown singlet. All color correction is done down inside the tube.

Another variation of this is the Schuppman medial telescope which uses a similar concept of full aperture singlet with sub-aperture correctors. Most of these designs are long focus with limited field sizes, but for visual planetary they would be well suited.

Rolando