[alt-photo] Re: a large-format horizontal enlarger with tilt shift mechanism?

[Richard Knoppow]

----- Original Message ----- 
From: "Ryuji Suzuki" <rs at silvergrain.org>
To: <alt-photo-process-list at lists.altphotolist.org>
Sent: Monday, November 29, 2010 2:12 PM
Subject: [alt-photo] Re: a large-format horizontal enlarger 
with tilt shift mechanism?


> From: Greg Schmitz <coldbay1 at gmail.com>
> Subject: [alt-photo] Re: a large-format horizontal 
> enlarger with tilt shift mechanism?
> Date: Sun, 28 Nov 2010 23:49:13 -0900
>
>> There is also the Procabin 67 projector - which has a 
>> good
>> reputation, if format is not an issue for you.
>
> Since I'd be projecting an inkjet digital positive, it's
> probably better to start with a larger size.
>
>> Are you trying to make prints on a photosensitive 
>> material
>> or display what you already have - not sure since you
>> referred to a "projector?"
>
> Neither.
>
> I'm projecting an image on rear projection screen, and 
> have
> some foreground subject (still life or live model or what 
> not)
> lit by studio flash system, and photograph a new image. 
> This
> technique used to be common in movies (using continuous 
> light
> source) but much of it got replaced by digital editing 
> process
> nowadays. Sure, Photoshop CS5 has a new feature called 
> "refine
> edge" and it's easier to cut out a picture and place it on
> another layer of background image, but I'd rather prefer 
> to do
> this in actual physical space like the old days.
>
> If alt process means doing something in ways other than
> the mainstream methodology, I think this sure qualifies...
>
     I think you would do best by making a projector from a 
view camera. You would have to build a suitable back to take 
a holder and to match to the light source. For large screen 
projection some sort of condenser source is necessary. One 
can use a parabolic reflector as was done by Elwood in their 
enlargers but making such a mirror might be expensive. 
Whatever the source it must provide even illumination 
especially the structure of the lamp should not be imaged on 
the screen.
     Ancient motion picture practice was to use lantern 
slide size transparencies for rear projection of stills. One 
problem is that the fall off of illumination of the 
projector adds to the fall off in the camera. In motion 
picture practice this was minimized by using the longest 
throw possible. Rear projection for both still and moving 
images was often done using two connected stages so that the 
projector could be placed well back of the screen. Various 
typse of "high-gain" screens were experimented with. Ideally 
the screen would be a Fresnel to concentrate the light from 
the projector to the camera but it would be limited to 
distances for both that worked. A diffusion source would 
probably have too much loss. Getting enough light is 
definitely a problem and is not trivial.
     Since the distance of the lens from the image is long a 
normal camera lens used with the front facing the projection 
screen would be closer to its optimum correction than an 
enlarging lens. I should mention here that any lens with 
fixed elements is completely corrected at only one subject 
distance. For camera lenses this is infinity or close to it; 
for an enlarging lens it is at whatever distance corresponds 
to the magnification ratio the lens is expected to be used 
for. There are special lenses for photo-mural use. Beause 
light is an issue the lens must be one that has good 
performance at large openings.
     In the past there have been projectors made for stage 
presentation that might work for this. I have no idea where 
to find them now but its worth doing some searching.
    Good luck and success with your project.

--
Richard Knoppow
Los Angeles, CA, USA
dickburk at ix.netcom.com