Linear Light Field Capture

Linear Capture Overview

A compressed output of a Linear Capture, rendered in Unreal Engine.
Linear capture of light fields is one of the most common light field capture methods, either in the physical realm with a camera rail, or in digital tools like Blender, Unreal, Unity, 3ds Max, Cinema 4D, and others. If you can move a camera left to right (or right to left), you're set!
Okay, so what are the rules? How much should my camera travel? How far should my subject be from my camera? Great questions! There are a few formulas that will determine where to position your subject and how far your camera will need to travel.

Visual Explanation

In this example , we have a camera with an FOV (field of view) of 58 degrees (equivalent to a 39mm lens). We can see through the visualization that there's a specific area where the two camera views overlap and some areas at the edges where they don't. So, what's the deal here? In short, as long as your subject is within the overlapping view cone and is visible in all of your views, you'll be able to get a great light field.
The distance between these two triangles is labeled as the travel and the height of the intersection is labeled as the distance. The triangle we want to solve for is actually the white triangle in the middle there, but split in 2 to give us a right angle.
We've got this triangle now, but what does this mean? Will my subject have to be at the focal point between these two views? Not exactly! What we've just determined is the minimum distance in which your subject can be relative to your camera. For a proper photoset, you'll want to ensure that your subject is in the purple region, meaning that it's visible in every view in between!
You can see in the image set above that 48 different triangles are overlapped on top of one another. This is representative of the captures you'll make, where each triangle represents 1 view. You can see that while the inner triangles overlap at different points with one another, the only point where all views overlap is still the original triangle we uncovered in our first steps above.

Subject Size, Camera Distance, and Travel Distance

In general, the closer your subject is to the tip of the triangle, the closer it is to the maximum depth the Looking Glass can provide at maximum focus. This means that in HoloPlay Studio, you'll have to slide the focus slider all the way to the maximum in order to get your object in focus. In practice, this isn't great, since it gives you less freedom overall with the image.
Instead, what you'll want to do is position your subject a bit further away from the inflection point of all these views. This will give you more freedom overall with the values you can set focus to within HoloPlay Studio.

Rules and Mathematics

This formula links the distance of travel to the minimum distance of the camera to the subject. This is dependent on the field of view of your camera. In this example, we're using a camera with a field of view of 58 degrees, or a 39mm lens, for those more photographically inclined.
tan⁑(cameraFOV/2)=(Travel/2)/distance\tan(camera FOV/2) = (Travel/2)/distance
Whoa, there! That's a bunch of math, what's going on?! Don't worry about this formula too much, it's actually rather simple! In order to determine the distance to the subject, we'll need to plug in our camera's FOV, then this formula will give us the relationship between travel and distance.
Let's say we're using a camera with a 58 degree FOV. In this case, our formula would become:
tan⁑(58/2)=(Travel/2)/distance\tan(58/2) = (Travel/2)/distance
tan⁑(29)=(Travel/2)/distance\tan(29) = (Travel/2)/distance
.55=(Travel/2)/distance.55 = (Travel/2)/distance
distanceβˆ—.55=Travel/2distance*.55 = Travel/2
distanceβˆ—1.1=Traveldistance * 1.1 = Travel

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If you have any questions about light field capture you can reach out to the team on Discord or post feedback or requests at our feedback forum!