"Medium" Thinned CCDs

[Tom Droege]

Posted to CCD-world:
-+-+-+-
Tass is an amateur/professional group that is attempting to survey all the
sky all the time in simultaneous filters.  The cameras just being placed in
operation are duals with V and I filters.  They have 400mm f/4 optics which
should get decent all sky measurement to mag 15.  Depending on our strategy
we should get around to the whole sky every month or so with the 16 V-I
cameras under construction.  We also have lenses for 4 B - R cameras.  To
keep the cost down and because this is a survey, we glue the filters into
place and use camera-filter combinations with narrow band lenses.  

Most professionals seem to encourage us to do this project.  

I am financing this out of my pocket.  Some people when they retire buy
expensive automobiles.  I build survey cameras and give them away.  So far
I have spent $100-200 thousand dollars on this project.  I don't like to
add it up.  We are beginning to publish from the data from the first round
of cameras.   Given the cost of thinned CCDs I will not finance the B part
of the survey.

OK, I know the people on this list have good thinned CCDs squirreled away
in safes.  I also know the way the world works.  They will stay there as
back ups until they are no longer useful to anyone.  

I would like to have you consider donating them to the tass project.  We
could then do the B, R part of the project.  I assume that a BVRI survey
will be more useful than just a VI survey.  Some day people will say why
wasn't tass supported to do the B part of the survey.  Well, I intend to
make everyone feel guilty when the time comes. 

1)  We can use noisy chips.   Do you have chips in your safe that you will
not use because they have noisy amplifiers?  The discussion seems to
indicate that you have.  These are just fine for tass.  We have 7 arc
second pixels and are operating mostly from amateur locations.  The sky is
always much brighter than the amplifier noise even at a good location.   50
e- noise would not be seen.  I doubt that any of you have chips whose
amplifiers have that much noise.   

2)  "Small" chips are right for us.  Do you have 2k x 2k thinned chips in
your safe that work and now have shifted to 2k x 4k chips?  We can put them
to good use.  

OK, we have not proven ourselves yet.  We will soon.  At the moment we are
suffering the usual problems of getting a major project up.  We are down to
the last big problem, I believe.  I have 40 specially designed lenses
sitting in my garage and they all have greater than design coma.  Sigh!
(Possibly the B lenses are OK - but we have no B sensitive CCDs to use with
them.)  Somewhere along the line of volunteers that designed them a mistake
was made and we have wrong spacers in the 5 element lenses.  But we will
fix this and soon the V I survey will be running.  

I estimate it would take a year for any of you to decide to give us chips,
and another year to figure out how to do it through the government
bureaucracy.  We will be ready before that time.  No, I have not approached
any funding agency.  I figure I can either do the project, or attempt to
get it funded.  I don't have the energy to do both.  If I can't get thinned
CCDs with minimal effort, we just won't do the B part of the survey. 

Tass wants to do this job, it is not so necessary for us to get the credit.
 We could name the whole project after someone who gave us a thinned CCD,
or whatever works.   It is also good for your government funding to support
amateur projects that get the general public involved.  We do that.  Just
see our web page.  

Tom Droege
-+-+-+-
For information about CCD-world, send email to owner-CCD-world at cfht.hawaii.edu.