Brush and Display Together: Camera Lucida for Light Strokes
Introduction: Brush and Display Together: Camera Lucida for Light Strokes
While Light Strokes let's you paint on the iPad using real brushes and other physical tools, the painting surface isn't on the iPad itself. That makes it difficult to know exactly where your brush is going to end up in your painting when you touch it to that separate surface. This Instructable shows how to build a camera lucida that puts the iPad's display right on the painting surface. That way you can see where you're about to start a stroke, and monitor the digital paint flowing from the actual brush (or other tool) during the course of each stroke, as shown in the video above. This improved feedback allows for much greater control in the Light Strokes painting process (as is taken for granted in both traditional media and touchscreens). If you look at my work on Instagram @rglightsrokes (where I've been posting at least one new painting a day since Jan. 1, 2022), you can see how much more detail I've been able to achieve since adding a camera lucida in mid-February 2022.
There are some excellent camera lucidas on the market, used to assist drawing by superimposing a virtual image of a scene onto a nearby surface where it can be traced. Unfortunately none of those are suitable for this application because:
a. The angle they require between the scene to be drawn and the drawing surface (60° to 90°) is much greater than the 36° angle between the iPad and the Light Strokes painting surface.
b. 983
They're only wide enough for a single eye, since they work with scenes much further away than the tracing surface, which puts their virtual images well below that surface, where binocular vision would only impede tracing. But we'll put the image of the iPad right onto the painting surface, and make the camera lucida wide enough for both eyes to see through it at once, for good depth perception of the approaching brush.
Supplies
* One glass first surface mirror, 6" x 2-3/4" x 1/16" (Boston Craftworks Front Surface Mirror - GLASS)
* One glass 50/50 beamsplitter, 6" x 3" X 5/64" (Two Way Mirrors Teleprompter Mirror 50R/50T)
* Four pieces of carbon fiber tubing, 0.240" O.D.: two 21" long, and two 20" long (TAP Plastics)
* One piece Transparent Bronze acrylic, 7-1/4" x 6-1/2" x 1/8" (TAP Plastics) (and optionally pieces of the same size in other shades such as Lt Smoke and/or Dark Smoke)
* One 5-3/4" long piece of silicone tubing, 1/16" I.D. x 1/8" O.D. (OCS Parts)
* 200 grams PLA (Duramic 3D PLA PLUS)
* A few drops of a flexible adhesive such as E6000 (Eclectic Products E6000 Craft) or silicone sealant (GE Sealants GE5030)
* Eight #8-32 x 1/2" round head machine screws
* Two #8-32 x 3/4" round head machine screws
* Four #8-32 x 3/4" flat head machine screws
* Fourteen #8-32 nuts
* Six #8 flat washers
Other than the usual hand tools you will need:
* 3D printer
* Power drill
* Tools for cutting thin glass (the same as used to cut the mirrors for Light Strokes itself)
Step 1: How It Works
The first diagram shows how the components of the camera lucida are located relative to the Light Strokes hardware, seen from the side. Light rays from the iPad pass through the beamsplitter, are reflected from the mirror, and then from the beamsplitter into the eye. Light rays from the painting surface simply pass through the beamsplitter and directly into the eye, following the same paths as those from corresponding parts of the iPad display after their final reflection.
That's because the axis where the mirror and beamsplitter would meet is equidistant from both the iPad and painting surface. The angle between the beamsplitter and the mirror is 18°, which causes the twice-reflected image of the iPad's display to be rotated about that axis through 2 x 18° = 36°, where it lines up with the painting surface. The mirror and beamsplitter can also pivot together around that axis without affecting that alignment.
The second diagram shows the components that hold the camera lucida at that location. One can easily switch between looking at the virtual image of the iPad on the painting surface, and by slightly raising one's eyes, viewing the iPad directly, over the top of the camera lucida. 582