Posts Made By: Robert Apruzese

Hi Roland; I was wondering when you will be able to announce the replacements for your oil spaced 105mm f/6 and 130mm f/6
scopes? Will they be air spaced like the new 160mm? Will they be "all spherical"?
Thanks.

Go to the Woden optics home page, http://www.wodenoptics.com/
and click on the link that says diagonal
calculator. The program that downloads works perfectly.

The following was borrowed from Roger Ceragioli's refractor web site; would anyone care to comment (e.g Roland, etc.)

"I have seen one 10" f/9 triplet from a commercial maker and it showed no visible color error. That is not to say, however, that the telescope gave a stellar performance. On the contrary, by introducing airgaps back into apochromatic lenses--which inevitably show strong internal curves--we bring back the old problems of the Zeiss B and Taylor triplets, namely their great sensitivity to temperature and to internal alignment. I was rather aghast to see the severe spherical aberration in the 10" lens, due to the falling temperature that night. Because of the great thickness and mass of the lens, as well as the fluor-crown's very high coefficient of thermal expansion and its insulted position in the middle of the lens, this $40,000US extravagent objective never performed as well that night as a decent 10" Newtonian would. My impression is that the owner found this true on other nights as well and lamented that the lens could not keep up with the falling temperature. Other examples of this type of instrument also show the same problem I am told by my optical acquaintances. So while the smaller lenses of this type in the 160mm range may be fine, it would appear to me that the makers of the larger lenses have overreached the limits of what triplet apos are capable of--at least the air-spaced variety. It is a shame that oiling, the revolutionary technical advance introduced by Wolfgang Busch and Roland Christen almost 30 years ago, has been abandoned. Oiled lenses even of rather large thickness show much more moderate variation of spherical aberration during cool-down in my experience. Perhaps the large air-spaced beasts will work well on tropical islands where the diurnal temperature variation is minimal. But people who live in temperate climates may wish to be careful of large air-spaced ED lenses."

April 2006 - January 4, 2013, best cat ever.

If an air spaced objective has too wide an air space, will this contribute to under correction or over correction? Same question if the air space if too narrow. Final question: For a 60mm f/16 objective, does anyone have an educated guess as to what the optimum air space gap would be ? Thanks in advance.

Last January I purchased a TMB lens in cell from Markus and had a machine shop adapt the cell to my U.O. 80mm refractor. The lens is optically perfect, period. No color on anything, perfect star images, etc. If I didn't already have a tube assembly for the lens, I would have opted for a light tube version, as the lens plus cell is much heavier than the achromat lens + cell it replaced. You really can't go wrong with a TMB lens. Comparisons to AP or Tak or TV are really pointless in my opinion. They all make lenses that are, from a practical standpoint, perfect. Go with what is available and affordble. For me it was the TMB lens in cell.

This is what Roland Christen had to say in a posting in this forum on 5/6/2004 about the optical problems of the 102/6:

"did one more simulation with F1 glass (which causes overcorrection of spherical and blue chromatic) and added a turned down edge. The result is a nice yellow halo at focus. The size of the yellow halo will depend on the amount of turn down.

Roland Christen"


So, a turned down edge does explain the yellow halo seen when the objective lens is not stopped down. By the way, a turned down edge is an "edge" defect.

With respect to buying any Burgess scopes used, "caveat emptor" should be the rule of thumb. But I still cannot condone sellers stretching the truth and screwing unsuspecting buyers. The seller should be sending the scope back to BO, not unloading it on some poor sucker.

This is Marmalade, my 18 year old sweetie.

Parallax instruments sells extruded, seamless aluminum tubing, their web page is: http://www.parallaxinstruments.com/index2.html