P3D Re: Viewer variable illumination

[Steve Berezin <sbere@xxxxxxxxxxxxx>]

"Dr. George A. Themelis" wrote:
> 
> >From: sbere@xxxxxxxxxxxxx (Steve Berezin)
> 
> Correction:  By "AC current" you mean 110 VAC from a house outlet.
> It is the high voltage that makes possible to use simple rheostats

Does this mean when I get a 110V battery I can use a household rheostat
:-)

> (like in Kodaslide and Realist AC viewers) not the AC current per se.
> Also, I do make a series of voltage-regulated power supplies to power
> 2.5V light bulbs.  Yes, they are time-consuming for me to make but
> they are not too expensive and they are well-worth it IMO.

I was referring to actually adding the voltage regulated power supply
into the body of the viewer.  Adding it to the outside is a simpler
process.  

> 
> >I found that graduations in brightness can also be achieved by moving
> >the reflector closer to the light source.
> 
> There is a danger here:  The closer the bulb is to the reflector,
> the steeper the illumination drop-off at the edges, and this
> can be a problem if the viewer is supposed to support 7p formats or
> wider.  

The LifeLike, unless opened up, can only view Realist and smaller
format.  I have noticed much less illumination drop off than with
earlier era viewers.  Like many of Seaton Rochwite's other designs the
LifeLike does have certain peculiarities.  As you mentioned, I have
noticed in illuminating viewers the size of the image does make drop off
more of an issue.  For example illuminating a View-Master viewer is much
easier than lighting a medium format viewer.  


The ideal would be to have the bulb located at equal distances
> from all points of the reflector.  You lose intensity but you gain
> uniformity.  What is more important for you?  (Such design does not
> exist... the deWijs "Comby" light supply has two halogen bulbs, one
> for each side of the slide).


I haven't seen the light supply for the Comby.  Can you describe how it
works?  Does it use a halogen bulb and a diffuser (along with a
reflector) or does it use just a reflector mechanism?

In response to Al Knecht Dr. T Mentioned:

>  noticed you mentioned ,"finger-free lighting" in your list of viewer 
> desirable qualities.  This feature is not in my list, as I believe it
> causes more trouble that benefits.  In a sequential or demonstration 
> viewer I understand how this is an advantage but in a single-slide 
> viewer it is easy to press a button while looking through the viewer.  
> The drawback of these designs (one example is the Life-Like viewer) is 
> that this "finger-free" operation is achieved with electrical contacts 
> that are not easily accessible for cleaning.  Flicker is common at 
> points of contacts and these need to be cleaned from time to time.  
> More contacts which not easily accessible is a problem IMO.
> 

I am not sure I understand this correctly. I have not found these
contacts much less assessable than the contacts of any 1950s style
viewers.   They seem to involve taking the top off of the viewer and
abrading the area where the contacts (copper 'spring' material) are
pressed together when a slide is placed in the viewer.  The contact
actually seems slightly more reliable than the contact involving the top
button and the contact on the other 1950's era viewers. The actual on
and off switching is done with a normally closed microswitch on the
bottom of the viewer which seems relatively trouble free compared to
on/off switches of most vintage viewers.  


> 
> George Themelis

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Steve Berezin
Berezin Stereo Photography Products
21686 Abedul
Mission Viejo, CA 92691
USA