Re: [APML]: Re: Vacuum pump

[Brad Wallis <wallis@pepe.jpl.nasa.gov>]

I have a crummy editor ... so can not copy the question here ... sorry ..

here are the specs from marvac...


The MARVAC R-10 vacuum pump is a Single Stage Mechanical vacuum pump
It is a 1.5 CFM pump  and ... according to MARVAC .. its "ultimate
vacuum" is about  100 microns

probable practical limit in a chamber with film and with no leaks
is probably no better than a 1 mm vacuum ....

def:  ULTIMATE VACUUM = minimum pressure this pump can pull when
      connected DIRECTLY to a vacuum guage... pumping nothing
      and with no leaks and no volume ...

Marvac Scientific Mfg Co...2931 Cloverdale Av...Concord, CA 94518
Phone: (510)825-4636


...........................

not sure how to answer that question  " is it worth it ? " ... I think you
can get the same results from a handpump or from some long purges with
nitrogen or cold FG ....  i know you can buy a serious pump in surplus for
less than 2x the cost of this pump .. BUT .. you'd have to be careful
and learn some vacuum info before you take that risk ...  a full up
high vac system is about $2K new ...

as i say at our HINTS piece on hypering ... " ANY HYPERING is better than
NO HYPERING" ( at least on Tech Pan !!! )  ( for the new color films, this
comparison is less dramatic ) .....

this pump will not pull the water out of the film ... that i can tell you ...
i really think that keeping things simple is best for most who are doing
astro-photo work ...  a hand pump is probably just fine or a nice long
purge ... even NO purge will get you a big boost ... and close to optimal
results ...  id really think that high vacuum is only for the real fanatics
who are shooting the FAINTEST nebulae and doing 2-3+ hour exposures and
who really need the extra boost  .. and i think there is not much to 
be gained moving from a purge or a low vac to a 1mm vacuum ... 

there should soon be another piece on "HOW TO BUILD A HYPERING SYSTEM"
at the webv site as well as a piece on GUIDING CHOICES .. as soon as
Robert can get some "free time" <HA!> <G> to make the web site revisions ...

Brad Wallis
http://voltaire.csun.edu/wallis_provin.html