Posted 30 January 2008 - 03:20 AM
Any one had the chance to use a Zeiss AS100/1000? I am really interested how good these are (were) as they use an aspheric doublet and one low dispersion schott element.
Any views appreciated, thanks.
Posted 30 January 2008 - 04:41 AM
I have no direct experience of the AS100/1000 but I own an AS110/1650, thus I may give you some infos (...Gerd has an AS130/1950 â€” luck him ! â€” so he may add his own views...;â€“)
These are *very* good (that "very good" usually spelled as "excellent"). They don't really use low dispersion elements, rather a Steinheil design with a leading Flint (KzF2/BK7). One surface is indeed aspherized to correct a residual fifth order spherical aberration in the green part of the spectrum. These AS are conceived as "planetary" instruments, so with a global correction shifted towards the red (which is indeed perfectly focused together with the green) where the more interesting planetary wavelengths are located. This is done at the expenses of the blue part of the spectrum which is heavily undercorrected. So much that this tends to produce almost no blue halo (blue light is too much defocused, so it becomes invisible), but rather a spurious bluish hue in the black sky.
Figure is *extremely well corrected* and *extremely smooth*. These scopes do not break under any reasonable magnification... No gain by using neither a Wratten #8 or a Semi-Apo filter (with this one colors are less warm but I find an induced lessening of both contrast and resolution, not to mention light).
Using a Zeiss binovier brings of course the best views, although I have to confess that most of the times I prefer the purity of the straight-through view where, using Zeiss Orthos, you don't quite see where the sky ends and the barrel begins...
The AS â€” conceived by Zeiss as "improved achromats" (what today is usually called semi-apo, whatever that means) â€” are supposed to have a 50% improvement in the color correction over a regular Fraunhofer BK7/F2 Achromat. In a week time I shall be putting my new AS63/840 (same design as the AS100 and AS110) against both a Telementor (C/63/840, regular Fraunhofer) and a Royal-Astro 60/1200 (idem Fraunhofer). Being f/13.3 +50% equal to f/20, I shall be able to let you know if these claims are true.
But this is just color correction. The rest of the pudding is in the overall correction and smoothness of figure. And here these AS are among the best.
Hope this helps,
Posted 30 January 2008 - 06:29 AM
Posted 30 January 2008 - 06:41 AM
I am lucky to have some friends who give me the opportunity to observe with several Zeiss stuff,
but not with a AS 100/1000
My experiences relate to Zeiss
C50/540, E 50/540, C63/840, C80/500, AS 80/1200, C110/750, AS 110/1650, AS 130/1950, AS 150/2250.
Also APQ 100/640, APQ 130/1000, APQ 150/1200
I can show you a table from the archive of Wolfgang Rohr-Germany where you can see something interesting
about the different colour errors of the AS lenses.
Dieter Lichtenknecker, Germany describes in the sixties the colour error with a value,
the RC (Rest Chromasie) which means rest colour error at 1mm exit pupil.
The effective value RCeff is RC/Exit Pupil
In the table color error smaller than the value of 1 means Apochromat.
A value between 1 and 2 means Semi-Apochromat.
A value greater than 2 means Achromat.
A BK7/F2 110/1650 Achromat has a colour error value of 6.7 at 1mm exit pupil.
You can see how well corrected a AS lens is, also the AS 100/1000.
(Ed, your TAK TSA is much better colour corrected)
The AS lens is a invention from August Sonnefeld in 1926.
It was manufactured by Carl Zeiss Jena from 1926 until 1995.
Sorry for my bad English language.
Posted 30 January 2008 - 07:55 AM
That's quite an interesting table...!!! Thanks for sharing it...!
Would you please send a hi-res version to my private email address?
Thank you so much !
Posted 30 January 2008 - 09:08 AM
I had a Zeiss AS100/1000 for many years. The correction and figure of the lens was first class, couldn't ask for better. As far as the chromatic aberration, there is some. Of the Zeiss AS scopes, I have owned the AS63/840, the AS80/1200 and the AS100/1000. The AS80/1200 had virtually no CA, but the 63 and 100 showed some; conclusion - the short-flint element in the AS lens does very well at f/15. In his landmark article in the Feb. 1963 Applied Optics, entitled "Planetary Telescopesâ€, James G. Baker called the Zeiss AS lens a semi-aprochromat.; I donâ€™t believe Zeiss ever claimed that. The AS100 is a great scope and you really canâ€™t go wrong with it. The value is going up on these scopes each year and so if you later decide to sell it, you wonâ€™t loose anything.
Posted 30 January 2008 - 10:56 AM
I have not been able to find much info on the web on these fine refractors so this really helps.
Posted 01 February 2008 - 04:21 AM
the existence of a APQ 200 lens is almost as mysterious and legendary as the Holy Grail
Posted 02 February 2008 - 09:41 PM
I had not heard of an APQ200 either. The last catalog I have from 1995 only lists the APQ100, APQ130 and APQ150. Do you know when it was supposedly made?
I thought that the Zeiss Presto was the only mysterious Zeiss apo. When I contacted Dr. Wimmer at Zeiss about those, he said that only about 30 were ever made and they were prototypes and only a little more than a handful ever found there way into an OTA.
Posted 03 February 2008 - 08:03 AM
Posted 06 February 2008 - 04:29 AM
in the mid 90ties Zeiss has planned to make a APQ 200 lens.
Before any opportunity to order one, the Executive Board in Jena approved the closure of the sector amateur telescope.
So nobody knows except the Zeiss people whether such a lens was made.
It is a myth.
Maybe one day, one plunges into?