RE: One more thing about light boxes.

["Creager, Robert S" <CreagRS@LOUISVILLE.STORTEK.COM>]

A remarkable lack of comments for this idea (or are we waiting for Arne to
come back and weigh in).  This seems like a reasonable idea (from a physical
sense, not necessarily a logical sense), and I'm betting we can trigger the
flash(s) from a parallel port.  Just to spark some noise, what about using
disposable flash bulbs (those cubes or strips)?  Or do they make those
anymore?

Later,
Rob

> -----Original Message-----
> From: Chris Albertson [mailto:chrisalbertson90278@yahoo.com]
> Sent: Thursday, November 08, 2001 1:37 AM
> To: Tom Droege; tass@listserv.wwa.com
> Subject: Re: One more thing about light boxes.
> 
> 
> 
> Tom,
> 
> Why not use a strobe light?  Just a normal flash like
> on a 35 mm camera.  These have closely controlled color
> temperature (same as sunlight) and the good ones have
> repeatable light output that is adjustable over four
> to six powers of two.  There is no warm up period and
> you trigger them by closing a contact.   You do not
> have to worry about it aging.  If the strobe is to
> bright you can get ND gel filters from B&H Photo for
> a few bucks
> 
> Best of all the flash provides 100% shutter efficiency.
> This gets around the problem of the Mk IV's slow moving
> shutter.
> 
> All of the methods of making even illumination depend on 
> mixer boxes.  The best
> shape is a sphere because it lacks corners
> and edges.  
> 
> Tom Droege wrote:
> > 
> > You can't dim a tungsten lamp.  You have to run it at the 
> right temperature
> > to get something that has the right spectrum.  Now you have 
> something that
> > ages. Since the filament wears over time, it is a big 
> project to adjust the
> > illumination.  You have to do it with neutral density 
> filters.  These have
> > problems of their own.  Even so, you can't count on the 
> spectrum being
> > constant by just adjusting the brightness.  You really have 
> to take a
> > spectrum.  The whole thing gets really complicated at the 
> 0.001 level where
> > we want to work.
> > 
> > I think it may give better results to use several LEDs of 
> different colors
> > and pulse them.  These can be made pretty well behaved.  I 
> like to drive
> > them with 1-2 ns 100 volt pulses and put an ampere or so through
> > them.  This makes a pretty uniform pulse.  Many of the 
> problems you have
> > with getting uniform light out of an LED go away when you 
> pulse them with
> > an avalanche transistor.  There are temperature effects and 
> the like that
> > are hard to control at low voltage.  Now the brightness can 
> be adjusted by
> > how many pulses one puts in the 100 second open time.  One 
> can easily get a
> > million to one dynamic range.
> > 
> > I have tested PM tubes this way at Fermilab, and got very 
> nice linearity
> > curves over 6 decades.  I was really testing that my electronics was
> > linear.  One does this by running the PM tube into a 
> cascode amplifier for
> > the fans of such things.
> > 
> > This scheme allows one to make nice linearity curves.   
> Even Andrew has not
> > yet asked for linearity data on the CCD.  We probably need to check
> > linearity as we get near full well.  We could get it this way.
> > 
> > As you all can see, this is a topic with far more 
> discussion than action.
> > 
> > Tom Droege
> 
> -- 
> 
> --
>    Chris Albertson             
>    Redondo Beach, California
>    home:   310-376-1029   chrisalbertson90278@yahoo.com
>    cell:   310-990-7550
>    office: 310-336-5189   Christopher.J.Albertson@aero.org
>