Conference hydra::amiga_v1

                   -< Digitizing 35mm Slides with DIGIVIEW >-
    
When I first got DigiView, I tried using my RCA color camera and quickly 
realized that the process of first taking a color picture, only to have to 
digitize the black and white component through the color wheel, was going to 
give inferior results. The "standard" B/W camera you mentioned is "a must".
This camera allows you to adjust the position of the imaging tube within the 
camera to allow you to adjust the focus down to an inch or less.

I also tried to make my own color wheel using various colored photographic 
filters (the kind used in studios and movie sets for lighting) but found that
the color pallette in DigiView is initially balanced for the filters that THEY
provide. There is even a difference in the filters/balance between my DV and the
next rev up (Gold). DigiView Gold is balanced for use with fluorescent lights. 

The best results I've had were with a small light box I built. It is lit
internally with an incandescent bulb. It has a Fresnel (flat) lens near the top
which is covered with a frosted white glass on which the slide sits. The lens is
important because it re-directs the light at the edges of the slide so that it
focuses on the camera lens rather than diverging out to where it will do no
good. This avoids uneven hot spots in the center of the picture since the light
from the edges now ends up at the camera. I haven't noticed any differences in
the results I get when the iris is open or closed, unless the light box is TOO
bright. I usually leave the lens wide open. BTW, since DV allows you to invert
your image to negative, you can also "print" your B&W negatives by simply
putting a negative on the frosted glass and holding it down with another small
piece of glass. 

I built a camera stand for less than $10 using plumbing pipes and flanges, etc.
You can also build a "DigiDroid" to automatically rotate the color wheel. John
Bernard posted the plans elsewhere in this conference. It only cost about $10 to
build. I wouldn't leave home without it. 

Dave

    Thanks for all the input Dave.  Perhaps you could answer a few more
    questions about the slide box you built.
                                                                          
    What size/watt incandescent bulb are you using?  Since I have DV Gold
    should I use a fluorescent lamp?
                                                                   
    Whats a Fresnel lens?
    
    Any suggestions where to purchase a Fresnel lens and frosted glass?
    A Camera shop?  I guess a glass dealer would have frosted glass.
    
    Thanks Again,                                                    
    
    ...Ed

    When I needed frosted glass I went to Edmund's but it's very expensive. 
    i couldn't tell from the directions above whether it's for diffusing
    light onto the subject, but if it is there are safer ways.  Glass in
    proximity to a hot light can crack suddenly in a cold draft or no
    apparent reason.
    
    Anyway, fresnel lenses are also available from Edmund's, in fact some
    of Edmund's stuff is no available from supplusers they sold it to for
    less.  A fresnel lens is a flat lens with concentric rings of rounded
    prisms that bend the light the same way a conventional lens would. 
    they are used in theatrical spotlights, on overhead projectors (under
    the glass that's under the transparency), and in outdoor cigar lights
    ;-).  It is possible to make radio frequency fresnel lenses with
    alternating concentric rings of conductors and open space.
    Glass Fresnel lenses are expensive, but you can't put plastic next to a
    light.  The fresnel lenses in spotlights are very thick for dissapting
    heat, and deliberating bumpy to diffuse the light a little.
    Tom

   <<< Note 3154.2 by AKOV11::SMITH "Reality, just a visible imagination?" >>>

<    Whats a Fresnel lens? Any suggestions where to purchase a Fresnel lens 
<    and frosted glass? A Camera shop?  I guess a glass dealer would have 
<    frosted glass.
    
This was answered in the previous note. Edmund Scientific is a good source for 
many of these type of items. In lieu of a fresnel (pronounced fra-nel') lens,
you might use a pair of condenser lenses such as are used in photographic
enlargers. Instead of frosted glass, you might use 'milk glass' such as might be
sold in shops which do stained glass crafts. It is more opaque and loses more
light but it also difuses the light better. 


The slide copy box I built looks something like this:


         Slide or negative ->   _______     
Milk glass or ground glass -> ___________   
              Fresnel lens ->|===========|  Ventilating holes
                             |           |__   __   __   __
                             |\
                             |  \  mirror set     __
                             |    \  at 45�      /  \  High intensity 12 volt
                             |      \            \__/  automotive light bulb.
                             |        \                
                             |__________\__________________

The box could be made of bent aluminum or plywood lined with aluminum foil to
increase light output. With a slide positioned on the ground glass, set the
camera up so that the slide fills the image field and focus the camera. Then
move the lamp in or out (left or right) until the fresnel lens focuses the light
at the aperture of the camera lens. At that point, the picture should be
uniformly illuminated. 

<    What size/watt incandescent bulb are you using?  Since I have DV Gold
<    should I use a fluorescent lamp?
                                                                   
If the automotive lamp doesn't have the correct color balance, and if you can't 
find a suitable light source, you might try to use a photographic filter 
designed to convert an incandescent source to look like fluorescent. I know 
there are filters to correct fluorescent light for use with daylight or tungsten
films. Otherwise, you may have to play with the color pallette.

Dave

Why can't you just use a small commercial light table?  Most use 
white translucent acrylic and provide a very even light source.  
You could pick up a small piece of this type of plastic at 
virtually any glass shop for next to nothing.  The advantage is 
that it is colorless.

Randy

<	Why can't you just use a small commercial light table?  Most use 
<	white translucent acrylic and provide a very even light source.  

You could. Trouble is, where are you going to get a light table as small as a 
coffee mug (or thereabouts)? I've got one, but it's about 12" x 18".

Dave

Mask it off with illustration board or mat board.  You could even 
make a little thing on the board to position the slide out of the 
leftover board.

Randy

 The folowing was extracted from Amiga World Dec 1989
	For Full color digitizing, mount a two-foot square piece of rear
 projection screen material- (wich can be purchased by the yard from:
		Rosco
		36 Bush Ave.
	 	Port Chester, NY 10573
		914/937-1300
		and
		1135 North Highland Ave.
		Los Angeles, CA 90038
		213/462-2233
    )  - onto a free-standing frame and project an image on it from the rear.
 The Digi-View camera records the image from the front of the screen, and 
 you don't have to worry about even lighting.
					
						Toby

Re .7

You missed my point. Of course it's easy to mask off the unwanted portion of the
light from a light table. My point was that who wants to have to buy and store a
large (and expensive) item when a small one will do.

Re .8
<	For Full color digitizing, mount a two-foot square piece of rear
<	projection screen material onto a free-standing frame and project 
<	an image on it from the rear. The Digi-View camera records the image 
<	from the front of the screen, and  you don't have to worry about even 
<	lighting.
					
The problem here is that you DO have to worry about uneven lighting. This is 
because the light coming through the center of the screen disperses, but with 
the majority going straight through to the camera. At the edges, the light is 
diverging from the main axis and a majority of the dispersed light STILL spreads
out away from the camera, thus leaving what appears to be a bright hot spot in 
the middle. The fresnel lens serves to redirect the diverging rays so that the 
same "number" of rays converges at the camera lens from ALL parts of the image.

Dave