What kind of filter for cooling fan?

I thought I'd try installing a cooling fan that blows across the face of
my Newtonian mirror (as outlined in Alan Adler's Jan 2002 Sky and
Telescope article). The problem I have is that I don't want to end up
sandblasting the surface of the mirror with whatever grime and dirt just
happens to be near the fan (just look at the back of your computer
sometime). What kind of filter material would work well for this type
of application? Is the standard foam stuff that is used on computers
good enough for outdoors applications?

Thanks

"Doug Brown" wrote in message
...
I thought I'd try installing a cooling fan that blows across the face of
my Newtonian mirror (as outlined in Alan Adler's Jan 2002 Sky and
Telescope article). The problem I have is that I don't want to end up
sandblasting the surface of the mirror with whatever grime and dirt just
happens to be near the fan (just look at the back of your computer
sometime). What kind of filter material would work well for this type
of application? Is the standard foam stuff that is used on computers
good enough for outdoors applications?

Thanks


Doug,

What kind of newt do you have?

Clear skies,

Tom

Doug,

What kind of newt do you have?

Clear skies,

Tom

It's an f/6 10" home made Newtonian.

Woulds it not be better to place the fan at the back of the mirror, in-between
the mirror cell mounts? I have seen this done with an Orion Optics scope
(British), using 3 small PC type cooling fans.

regards,

Geoff GJ

I'd have the fan draw air across the mirror, rather than blow it across
the mirror. No high velocity particles impacting the mirror that way.

Bryan

Doug Brown wrote:
I thought I'd try installing a cooling fan that blows across the face of
my Newtonian mirror (as outlined in Alan Adler's Jan 2002 Sky and
Telescope article). The problem I have is that I don't want to end up
sandblasting the surface of the mirror with whatever grime and dirt just
happens to be near the fan (just look at the back of your computer
sometime). What kind of filter material would work well for this type
of application? Is the standard foam stuff that is used on computers
good enough for outdoors applications?

Thanks

For blowing vs. sucking, see the Dob-fans Yahoo group.

David

wrote:

I'd have the fan draw air across the mirror, rather than blow it across
the mirror. No high velocity particles impacting the mirror that way.

Bryan

Doug Brown wrote:
I thought I'd try installing a cooling fan that blows across the face of
my Newtonian mirror (as outlined in Alan Adler's Jan 2002 Sky and
Telescope article). The problem I have is that I don't want to end up
sandblasting the surface of the mirror with whatever grime and dirt just
happens to be near the fan (just look at the back of your computer
sometime). What kind of filter material would work well for this type
of application? Is the standard foam stuff that is used on computers
good enough for outdoors applications?

Thanks

On 14 Aug 2003 10:17:53 -0700, (Thad Floryan) wrote:

wrote in message ...
I'd have the fan draw air across the mirror, rather than blow it across
the mirror. No high velocity particles impacting the mirror that way.

True, there'd only be low-velocity grit dragged across the mirror. :-)

Think, for a moment, where the air filter is located in your car.

But in the same thought, lets place into perspective how much vacuum
or "air movement" your cars carburator (for us who remember them) or
intake plenum makes compared to a tiny little fan that would fit into
the palm of your hand...
I myself would preferr the draw method, this way any bugs that get
sucked into the fan, have thier guts sprayed outside of my OTA.
As far as a filter material, Someone mentioned filter floss from a
fish tank filter... Thats PERFECT! And very cheap to replace instead
of washing..

Doug Brown wrote:
(snip)
: The problem I have is that I don't want to end up
: sandblasting the surface of the mirror with whatever grime and dirt just
: happens to be near the fan (just look at the back of your computer
: sometime).

How can you compare the two? Unless you install your computer OUTSIDE you
can't. An indoor fan has to deal with house dust. That, is what builds up
on the filter and/or blades. An outdoor fan will not see any of that ...
what WILL it see?? I dunno ... but, while a filter won't hurt .. I think
you're over reacting to a non-existant problem (but, hey, I could be
wrong)

Richard in Boston, MA, USA