Sinar Two-Sided, Partial Mirror for 4x5. Use???

[neil poulsen]

Along with other Sinar equipment, I have a two-sided, partial mirror that fits onto the back of a Sinar 4x5. By "partial" mirror, I mean that it reflects part of the light, and it also passes the remainder of light. On occasion, I see them up for sale on EBay.

I imagine that it's for copying, since the previous owner did copy work. But , I'd like to know its purpose, and how this partial mirror can be used?

[Greg]

539.11
Semi-reflecting 50/50% mirror
Solves lighting problems in close-ups, projects images to a background screen with front projection set-up and can be used for numerous special effects

quoted from August 1986 Sinar catalogue

Only used one one time to try to simulate a professor looking down at some microscope slides... Proved a lot easier to just lie on the floor and shot up through a large plate of glass with the microscope slides resting on the glass.

[David Hedley]

In the Sinar "Creative Large Format' book, they show a set up with the semi-mirror at 45° in front of the lens, and before the compendium lens shade. Consequently, the camera is simultaneously taking a picture both straight on (as normal), and also at 90° to the camera, where there is a screen with an image to be superimposed over the main scene.

Alternatively, it looks like the semi-mirror can be used to light a close-up subject directly from the front through the mirror.

An interesting piece of equipment, but not one I would use on a daily basis!

[LabRat]

Usually used as a beam splitter... Can combine two images if both were shot on a black background... (One example is the tired, old wedding image of bride in glass while hubby makes a toast...) Or projections/matte shots to add a background (life before fotoshop !!!)... But a PIA to set-up!!!

Then there's on-axis lighting for no shadows, or to shoot into cylinders, etc...

But one of the more practical applications was when a cinematographer showed me a rig he fashioned that split the beam with an adjustable white plex lightbox, that when mounted on camera, when looking at a contrasty scene, he would slowly turn up the light level, and in the dark shadows, it would combine with the lightbox image and raise the shadow level + reduce the (apparent) contrast... (This was probably useful for something???) Maybe for flashing shadow areas while exposing???

And maybe fun to use as an obie that gives the portrait sitters that mysterious retinal catchlight look like those cyborgs in the film "Blade Runner", or at least as a subtle fill light???

Would be fun to play with!!!

Steve K

[neil poulsen]

Sounds interesting. Seems like it would have to be a high-quality mirror to combine photos, and do some of the other things that have been described.

Mine can mount into a supplemental standard. So indeed, might be fun to experiment.

[rdenney]

But one of the more practical applications was when a cinematographer showed me a rig he fashioned that split the beam with an adjustable white plex lightbox, that when mounted on camera, when looking at a contrasty scene, he would slowly turn up the light level, and in the dark shadows, it would combine with the lightbox image and raise the shadow level + reduce the (apparent) contrast... (This was probably useful for something???) Maybe for flashing shadow areas while exposing???

That's the way the contrast control unit on a Bowens Illumitran works, but it doesn't use a semi-mirror--it just uses a piece of glass. And the effect is still too strong--when I play with that again, I will use a neutral-density gel to reduce the output of the contrast-control light source.

Rick "who has not yet been tempted to add one of these to his Sinar kit" Denney

[neil poulsen]

I can think of another application.

I built a device for copy work that shoots a laser beam perpendicularly from a painting. Mounting the semi-mirror onto the back of a 4x5 camera with the lens removed, if the beam reflects directly back to the laser, then the plane of film will be parallel to the plane of the painting. So, the painting could be on a tilted easel, and it would still be easy to make the two planes parallel.

To carry this a little further, being a semi-mirror, the laser would be seen from the rear of the camera. So, if the laser beam is centered on the mirror, then the film is centered at the location of the laser on the painting, making it easy to properly align the film to the painting.

All this of course, assumes that one is not using digital.

[Bob Salomon]

I can think of another application.

I built a device for copy work that shoots a laser beam perpendicularly from a painting. Mounting the semi-mirror onto the back of a 4x5 camera with the lens removed, if the beam reflects directly back to the laser, then the plane of film will be parallel to the plane of the painting. So, the painting could be on a tilted easel, and it would still be easy to make the two planes parallel.

To carry this a little further, being a semi-mirror, the laser would be seen from the rear of the camera. So, if the laser beam is centered on the mirror, then the film is centered at the location of the laser on the painting, making it easy to properly align the film to the painting.

All this of course, assumes that one is not using digital.
Why wouldn't this work on a view camera that accepts digital backs? You can always set up with the ground glass back in place to check alignment and then, after aligning, focusing, composing, replace it with the digital back.
But then couldn't you also do this with the laser going through a reflex viewing system on either film or digital?

[neil poulsen]

It would work fine. (If I had a digital back.) :)

It also works with a DSLR, but it's a little more trouble. If the laser centers on the lens cap, and at the same time, the location of the laser device (on the painting) centers in the viewfinder when viewing the painting, then the sensor is aligned with the artwork.

But, I'm careful to make sure I haven't forgotten to place the lens cap on the camera.

A friend and I did some copy work for a while, and in the beginning, we used gravity (and a level) to align the sensor vertically, and used dimensions to either side of the artwork to align horizontally. This meant that we had to keep the artwork vertical, implying that we had to, in some way, pin or use a sticky clay to attach the artwork to a wall. To me, that was unacceptable.

This device allowed us to simply rest the artwork on a non-vertical easel.

[Bob Salomon]

It would work fine. (If I had a digital back.) :)

It also works with a DSLR, but it's a little more trouble. If the laser centers on the lens cap, and at the same time, the location of the laser device (on the painting) centers in the viewfinder when viewing the painting, then the sensor is aligned with the artwork.

But, I'm careful to make sure I haven't forgotten to place the lens cap on the camera.

A friend and I did some copy work for a while, and in the beginning, we used gravity (and a level) to align the sensor vertically, and used dimensions to either side of the artwork to align horizontally. This meant that we had to keep the artwork vertical, implying that we had to, in some way, pin or use a sticky clay to attach the artwork to a wall. To me, that was unacceptable.

This device allowed us to simply rest the artwork on a non-vertical easel.

This is basically how a parallel mirror for alignment like a ZigAline works. Both Linhof and Hasselblad sold them as well for copy work.