Largest APO built in the last ~10 years?

John Steinberg wrote:
What are the current *practical* limits on size of an APO refractor?

I don't think the necessary material is available in blanks much larger
than about 14". Assuming you use a 1/3 diameter sub-aperture corrector
to achieve apochromatism, then it should be possible to achieve a
40-45" diameter apochromat.

Of course, you could always create a very large glass blank by
cementing together polygonal "puzzle pieces". I know this was done
back in the 1960's to create calcium fluoride lenses larger than the
available raw material would allow.

Using the latter technique should allow you to make a truly monumental
APO refractor, assuming that thermal expansion wouldn't cause cracking
in ordinary use.

I think if the survival of the species depended on it we could make an
apochromat considerably larger than 100" in diameter.
Brian
www.caldwellphotographic.com

What are the current *practical* limits on size of an APO refractor?

Pocketbook.

;-)

Chuck Taylor
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************************************

--
-John Steinberg
email: lid

What are the current *practical* limits on size of an APO refractor?

Obviously availibility of glass is the big problem, but even if glass
becomes available, as the size is increased, so does the deflection of
the glass under its own weight, this will definitely set a limit for
the size of very large apo. Another problem is the color correction, as
the aperture is increased so does the chromatic aberration, for
instance if a given formula results in an acceptable color correction
for a 6" F/8, a much larger apo based on a similar design may have to
go up to F/12 to f/15 to allow for the same color correction, resulting
in a huge & massive instrument. As the size is increased negatives pile
up big time making very large apo's not cost effective and or
practical.
My guess is that 12" is the practical limit for the super size apo with
fluorite element.

Thanks,
Vahe

vahe240d wrote:

My guess is that 12" is the practical limit for the super size apo with
fluorite element.


Actually, modelling after James Baker's suggestion, I found you might be
able to cheat a bit on that, e.g.:

http://users.rcn.com/rflrs/baker2-75z.len
http://users.rcn.com/rflrs/baker2-75z.txt

Thanks,
Vahe

Actually, modelling after James Baker's suggestion, I found you might
be
able to cheat a bit on that, e.g.:

Cheating no doubt will result in considerably larger apo, as long as
the design remains on paper or on the computer screen everything should
appear just fine. But try to build that, you now face tons of practical
problems that are non issue during the design. When you face these
practical problems the real fun begins, and cheating will not save the
day.

Thanks,
Vahe

John Steinberg wrote:
How big and what are the specs?
Where is it located?
Who built it?
What are the current *practical* limits on size of an APO refractor?

Believe Markus Ludes of APM has commissioned a 21 inch APO from LZOS
for his own personal use. This may be the largest APO on the planet.
Believe there are also a couple 14 inch APOs out there that were also
built by LZOS.

Cheers,
Tom Mack

On Fri, 14 Jan 2005 00:33:47 +0000, "Richard F.L.R. Snashall"
wrote:



vahe240d wrote:

My guess is that 12" is the practical limit for the super size apo with
fluorite element.


Actually, modelling after James Baker's suggestion, I found you might be
able to cheat a bit on that, e.g.:

http://users.rcn.com/rflrs/baker2-75z.len
http://users.rcn.com/rflrs/baker2-75z.txt

It's good that this is all speculation. Because if anyone were
going to spend the kind of money that would take, they could
invest in any kind of reflector, get a better instrument for
what, about 1/5th the cost? And the mirror could be larger too.
-Rich

RichA wrote:



It's good that this is all speculation. Because if anyone were
going to spend the kind of money that would take, they could
invest in any kind of reflector, get a better instrument for
what, about 1/5th the cost? And the mirror could be larger too.

Let me guess... you like reflectors over refractors?

-Rich

wrote:
John Steinberg wrote:
How big and what are the specs?
Where is it located?
Who built it?
What are the current *practical* limits on size of an APO
refractor?

Believe Markus Ludes of APM has commissioned a 21 inch APO from
LZOS
for his own personal use. This may be the largest APO on the
planet.
Believe there are also a couple 14 inch APOs out there that were also
built by LZOS.

Cheers,
Tom Mack

There is the ARIES 12" Fluorite doublet (in Japan) and it does work.
14" (kurtz-flint based) triplet APO by LZOS still wait it's buyer.
How it will performs under sky is still a question. Thermal problems
can be significant.
As for 21". There is no warranty, that it will be succesfully realized
and that it will really work - again thermal problems and figure
stability (due to gravity).


VD

wrote:

John Steinberg wrote:
How big and what are the specs?
Where is it located?
Who built it?
What are the current *practical* limits on size of an APO refractor?

Believe Markus Ludes of APM has commissioned a 21 inch APO from LZOS
for his own personal use.

That figures uber alles!



This may be the largest APO on the planet.
Believe there are also a couple 14 inch APOs out there that were also
built by LZOS.

Cheers,
Tom Mack