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Posts Made By: Markus Ludes

February 5, 2004 07:07 AM Forum: Equipment Talk

WANTED<<<Reflector vs. APO >>>WANTED

Posted By Markus Ludes


a 175 mm apo offers ultrahigh contrast , excellent choice for douple stars and Planets. Due its smaller aperture and no central obstructionit is also way less effected by seeing turbulences, which means the real good nights with 175 mm aperture will be many more than with larger size.

The SC scopes I know will have zero chance on Planets and douple stars against the Apo. On Deep Sky you may see in the SC a brigher Image but much less contrasty, so the Apo will show you some details in Deep Sky stuff which you will not see in the SC

The classic Newtonian can be optized for everything, but you need to accept to deal with tweaking the collim,ation, always , mirrors which need to be cleaned from time to time and a open tube which also will be effected very much by the seeing many times

Leaves the Mak. A bigger Mak 10" or 12" will be also way more often effected by seeing, but if you buy a very high quality Mak and you get seeing like we have had last year in Florida it will beats the Apo , excapt on widefield observing where the apo offers wider field due its shorter focallenght.

Solution: buy a Apo 175 for everyday use and a 16" Mak for the small faint stuff and best seeing for planets

best wishes

March 8, 2004 06:53 AM Forum: Refractors

Astigmatism Question, back to reality.

Posted By Markus Ludes


if you see astigmatism in a lens, no matter if achromat or apo or whatever, than mostly it is not in the glas.

there are several possibilities alone or together :

1, most comon problem in low priced achromats: cells are not matched in inside diameter with glas diameter, so lenses can shift sidewards
2, spaces are not using matched thickness.

how to correct such problem without return of the optics:
- you can drill for each lens at the edge of the cell with 120° spacings threads and use plastic screws, they can allow you to push the lens onto perfect axis

good luck

March 10, 2004 08:44 AM Forum: Chinese Optics Imports

Re: Bill Burgess, get back to basics.

Posted By Markus Ludes

If someone want such a scope with no delay, I mean from stock, we selling them all over the year here in europe and have happy owners

a review of our modell was posted here

I am self promoting this refractors as low power rich field refractors and cannot undelrine all findings of the reviewer

best wishes
Markus Ludes

March 11, 2004 09:13 AM Forum: Refractors

Symmetry in Star Testing

Posted By Markus Ludes

Alan say :No lens has perfect color correction, and there is always some variation in focus across the spectrum. For simplicity, assume we have a lens corrected for C and F. The green light focuses slightly closer to the lens than either the blue or red.

Markus : sorry but shall a real apo not show 3 wavelenghtes at excact same focuse ???????????

Alan say :.....Based on this, it is hard to see why there would be symmetry in white light. Different things are going on inside focus than outside focus. This will always be true, unless all colors come to exactly the same focus (reflector, anyone?).

Markus:if the optics is superb polished you will see a perfect symmetrie even in achromats with same contrast, only the colors you see on each side of focuse are diffrent.
The diffrence in a perfect corrected lenses between inside of focuse and outside of focuse is nothing than the diffrent colors, but the fressnell rings and here contrast must be 100% equal if the optics is perfect polished

Alan : If you want to see what the correction for spherical aberration is, you really need to isolate the green light.

Markus: Alan here above you are correct , but with a real superb Fraunhofer achromat design or other semiapo or apo design, all optimized for green , usual the spherical aberration on outer wavelenghte is very similar. Only photographic corrected systems show diffrent wavelenght optimisations.

Look again the the white lioght startest images of perfect corrected, achros, semiapos and apos and see its true, simply because its a physical law, that it have to be this way


March 22, 2004 07:41 AM Forum: APM

New TMB 25 mm aspheric Ortho 25 mm

Posted By Markus Ludes

next 25 mm TMB eyepiece image


March 30, 2004 09:13 AM Forum: APM

March 30, 2004 09:15 AM Forum: APM

April 30, 2004 04:21 AM Forum: Astro Binoculars

Filter for the clones from APM, Burgess ?

Posted By Markus Ludes

Sun filters can be always used because screwed on front of the objective, or just fittet over.

On our modell we use eyepieces with special filterthread, so we can offer custommade screw in filters

best wishes

April 30, 2004 08:59 AM Forum: APM

May 13, 2004 10:28 AM Forum: Maksutovs