solution and procedure for cleaning SCT corrector?

Upon bringing in my SCT from a recent observing session, I've noticed a few
dew/ frost spots on the corrector as well as some non-fingerprint smudges.
I lost my Celestron manual, but what is the procedure/ solution content for
cleaning the corrector?

Thanks,
John

Goto www.arksky.org and select "guides" from the menu on the left side of
the screen. About half a screen down on the guides window you will see "ASO
fine optics CLEANING SYSTEM: Part 1".
This is probably one of the safest and widely used methods you can use.
Do keep in mind however, no cleaning at all is usually the best option!
People with expensive optics often never touch the lens for cleaning or
otherwise. When selling a good scope you may be asked if the optics have
ever been cleaned. If you have to answer "YES" you could lose a sale.
George D
"John Lepps" wrote in message
nk.net...
Upon bringing in my SCT from a recent observing session, I've noticed a
few
dew/ frost spots on the corrector as well as some non-fingerprint smudges.
I lost my Celestron manual, but what is the procedure/ solution content
for
cleaning the corrector?

Thanks,
John

On Tue, 01 Feb 2005 19:23:56 GMT, "John Lepps" wrote:

Upon bringing in my SCT from a recent observing session, I've noticed a few
dew/ frost spots on the corrector as well as some non-fingerprint smudges.
I lost my Celestron manual, but what is the procedure/ solution content for
cleaning the corrector?

I've had excellent results for many years with Windex and Kleenex, both
by brand name. Probably more important than the exact formula you use
for cleaning is the need to gently remove dust first (by brushing,
blowing, or both). It is doubtful you will ever have problems with a
cleaning solution damaging the AR coating, but scratches are fairly easy
to make if you have something abrasive on the surface.

BTW, it is a good idea to keep the corrector spotless. Unlike a dirty
mirror, which only has minor impact on the image, a dirty corrector
seriously degrades contrast if you have any stray light at all hitting
it. Also, a clean corrector is considerably more resistant to dew
formation. I clean mine every week or two in the summer when dust and
pollen is about, and perhaps monthly in the winter.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

"Chris L Peterson" wrote in message
...
On Tue, 01 Feb 2005 19:23:56 GMT, "John Lepps" wrote:

Upon bringing in my SCT from a recent observing session, I've noticed a
few
dew/ frost spots on the corrector as well as some non-fingerprint
smudges.
I lost my Celestron manual, but what is the procedure/ solution content
for
cleaning the corrector?

I've had excellent results for many years with Windex and Kleenex, both
by brand name. Probably more important than the exact formula you use
for cleaning is the need to gently remove dust first (by brushing,
blowing, or both).

Yeah, I already tried the routine for trying to blow/ remove "dust".
However, what I've had is actually pollen stuck to the corrector after many
nights of dewing. I really wasn't concerned with it, but was concerned with
some of the small smudges I've gotten, made worse by regular dewing. Those
had to come off.

It is doubtful you will ever have problems with a
cleaning solution damaging the AR coating, but scratches are fairly easy
to make if you have something abrasive on the surface.

I guess that's why I don't apply pressure- just drag the cotton across the
surface.

BTW, it is a good idea to keep the corrector spotless. Unlike a dirty
mirror, which only has minor impact on the image, a dirty corrector
seriously degrades contrast if you have any stray light at all hitting
it. Also, a clean corrector is considerably more resistant to dew
formation. I clean mine every week or two in the summer when dust and
pollen is about, and perhaps monthly in the winter.

Never had to have your corrector recoated from frequent cleaning? According
to the great instuctions in the post by Duke, every time an optical surface
is cleaned, no matter what precautions are taken, some of the optical
coating comes off. I don't know this for a fact, but that's what I just
read.

Thanks for the info.

John


_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Wed, 02 Feb 2005 15:42:24 GMT, "John Lepps" wrote:

Yeah, I already tried the routine for trying to blow/ remove "dust".
However, what I've had is actually pollen stuck to the corrector after many
nights of dewing. I really wasn't concerned with it, but was concerned with
some of the small smudges I've gotten, made worse by regular dewing. Those
had to come off.

Pollen is a big concern- when combined with dew, it produces acids that
will etch your corrector coatings. The good news is that it won't
scratch, so whatever doesn't easily blow off can be lifted with fluid.
If you live in an area that has any significant air pollution, other
dust may also form acid when combined with dew. In any case, the
combination of a dirty corrector and cycles of dewing is far more likely
to damage your optics than anything you do while cleaning.


I guess that's why I don't apply pressure- just drag the cotton across the
surface.

It's safe enough to apply light pressure to a coated corrector.


Never had to have your corrector recoated from frequent cleaning? According
to the great instuctions in the post by Duke, every time an optical surface
is cleaned, no matter what precautions are taken, some of the optical
coating comes off. I don't know this for a fact, but that's what I just
read.

Technically that's true, but in the case of AR coated glass, you are
probably talking thousands of cleaning cycles before any coating loss
would become significant. One of my SCTs has had its corrector cleaned
~250 times, the other ~75 times, and both look as good as the day I got
them.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

John Lepps wrote:
"Chris L Peterson" wrote in message
...

[clip]


BTW, it is a good idea to keep the corrector spotless. Unlike a dirty
mirror, which only has minor impact on the image, a dirty corrector
seriously degrades contrast if you have any stray light at all hitting
it. Also, a clean corrector is considerably more resistant to dew
formation. I clean mine every week or two in the summer when dust and
pollen is about, and perhaps monthly in the winter.


Never had to have your corrector recoated from frequent cleaning? According
to the great instuctions in the post by Duke, every time an optical surface
is cleaned, no matter what precautions are taken, some of the optical
coating comes off. I don't know this for a fact, but that's what I just
read.

Thanks for the info.

John



________________________________________________ _

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com





J.L. and C.P.:


Windex or other compound containing ammonia liquid should not be used with
fluorite coated optics. The ammonia reacts with the coating.

Isopropyl alcohol is the best for fluorite coatings, says the maker of my
computer monitor that makes coated screens. That also cleans up
fingerprints in two or three applications with cotton. Technical and
reagent grade may be more expensive than necessary, and 75% drug store
Isopropyl alcohol may work well.

Two or three cleanings will clean off the thin film of airborne auto engine
oils that may be originate from the local expressway. you don't see the
film until you touch the lens surface. The glossy surface will become
noticeably darker and duller with cleaning. The transparent color changes
from glossy pink to a dull purple cast. Rubbing may In time wear off the
minutely thin layer of soft fluorite material.

Kleenex contains minute particulate dust abrasives and rough fibers and
should not be used.

I'm not certain that biologically clean medical cotton balls are that dust
and abrasive free. They probably are, however, I'd research that a bit.
Purpose-made optical cleaning cotton and pads are available.

Nice contributors have posted:

http://www.thermo.com/eThermo/CMA/PD...0001028574.pdf

http://astronomy.trilobytes.com.au/s...t.htm#cleaning


Ralph Hertle

On Wed, 02 Feb 2005 21:43:42 GMT, Ralph Hertle
wrote:

J.L. and C.P.:

Windex or other compound containing ammonia liquid should not be used with
fluorite coated optics. The ammonia reacts with the coating.

I'm not exactly sure what "fluorite" coatings are. However, I've used
Windex for years to clean standard magnesium fluoride AR coatings on my
telescopes, cameras, and also in the lab for laser optics.

White, unscented, unlotioned Kleenex is entirely free of abrasives. I've
looked at enough of it under the microscope. I've never scratched an
optic using Kleenex, and it works much better than pure cotton.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Wed, 2 Feb 2005 15:43:42 -0600, Ralph Hertle wrote
(in article ):


Windex or other compound containing ammonia liquid should not be used with
fluorite coated optics. The ammonia reacts with the coating.
.....
Kleenex contains minute particulate dust abrasives and rough fibers and
should not be used.


Al Nagler himself recommends both Windex and Kleenex. Please see:

http://www.televue.com/engine/page.asp?ID=143

John Lepps wrote:
Upon bringing in my SCT from a recent observing session, I've noticed
a few
dew/ frost spots on the corrector as well as some non-fingerprint
smudges.
I lost my Celestron manual, but what is the procedure/ solution
content for
cleaning the corrector?

Thanks,
John

you should clean off as much grit as you can with running water first.
then I found lightly washing the lens with ivory soap gets off the
fingerprints. isopropyl alchohol (drugstore variety) will rinse off the
residue. distilled water to rinse the alchohol and kleenex to remove
the water. if you dont remove the water you will get spots. you dont
necesairily need the last step because the spots dont affect
performance.

chloe

Bill Tschumy:


Bill Tschumy wrote:
On Wed, 2 Feb 2005 15:43:42 -0600, Ralph Hertle wrote
(in article ):


Windex or other compound containing ammonia liquid should not be used with
fluorite coated optics. The ammonia reacts with the coating.

....

Kleenex contains minute particulate dust abrasives and rough fibers and
should not be used.



Al Nagler himself recommends both Windex and Kleenex. Please see:

http://www.televue.com/engine/page.asp?ID=143







That's an excellent discussion.

Windex and some other cleaners that don't leave a residue and that do
contain ammonia probably can be used safely in certain types of glass
lenses, e.g., Pyrex. I understand that ammonia will damage fluorite
coatings, however.

That is a technical issue. and I don't doubt that experience has resulted
in some good knowledge of the matter.

Some Kleenex contains lotions, and that leaves an oily residue that can be
cleaned with some alcohols.

Polypropanol alcohol that is available at the drug store contains 75%
alcohol in distilled water. That doesn't leave any residues.

Other alcohols, e.g., the methanol or methanol/ethanol mixtures (of unknown
percentages in NJ) used for shellac thinners seem to work OK on coated
camera lenses with sterilized cotton. In NJ that mixture product may also
contain some other solvents in unknown amounts. The methanol/ethanol will
gradually wear away the abrasion resistance coatings on polycarbonate
eyewear lenses. In NJ 99% pure ethanol is available at liquor stores.

I wouldn't use auto windshield cleaners or preparations that promise to
shed water; they may contain silicones or other water repellents, and they
are difficult to remove from the windshield. They are not clear and streak.


Ralph Hertle