HDR Aquisition - Pano Head Setup

Before we begin.  Sorry this post has taken so long to finish.  Life gets in the way!  Enjoy!

Part of the art and science of taking good panoramic imagery is stitching together multiple images with as little parallax shift as possible.  This means you need to align the nodal point/entrance pupil around the center of your rotation axis of the panoramic head.

Most everyone I know refers to this "no-parallax" point of the lens as the "nodal point" but while writing this entry I have found that this is actually called the Entrance Pupil.   Here's a little bit of a cut and paste from that wikipedia entry.

The geometric location of the entrance pupil is the vertex of the camera's angle of view^[1] and consequently its center of perspective, perspective point, view point, projection centre^[2] or no-parallax point^[3]. When the optical system is physically rotated about its entrance pupil, the perspective geometry of its image does not change. In panoramic photography, for example, it is important to rotate or pivot the camera about its entrance pupil in order to avoid parallax errors in the final, stitched panorama^[4][5]. Depending on the lens design, the entrance pupil location on the optical axis may be behind, within or in front of the lens system; and even at infinite distance from the lens in the case of telecentric systems.

Ok now you know what then entrance pupil is what next.  Lets calibrate our Nodal Ninja.  The Nodal Ninja like most panoramic rigs operate in a similar manner.  You have to align your camera in 2 different axis in order to have your camera in the proper position on the pano head.

A. Align the center of your lens with the center rotation axis of your panoramic head.

We'll call this adjustment the left-right adjustment.  First mount the camera on the Horizontal arm.  Rotate the horizontal arm until the camera is pointed directly down at the center rotational point of the pano head.  Now adjust the "left-right" of the vertical arm until the lens is directly over the center rotational point.  It is sometimes easier to put a longer lens on the camera so you can see the center of the rig a big better.  Once you have this properly adjusted for your camera this setting will never change no matter what lens you have on the camera.

If this isn't correctly aligned you will get a broken image at the nadir point of a stitched panoramic.

John Houghton explains this very well.

An indication that the lateral position is not quite right is a broken, sawtooth edge to the head at the nadir in a stitched panorama (an unpatched nadir, of course).  The example on the right is a typical example:

The top of the head looks somewhat like a circular saw. In this case, the "teeth" are set for cutting with a clockwise rotation of the saw.  This indicates that the entrance pupil is offset to the left of the pano head axis, as viewed from the back of the camera, so the camera needs to be shifted a little to the right. If the saw is set for cutting with a counter-clockwise rotation, then the camera needs to be shifted to the left. (image to the right is from John's site) 

B. Align the entrance pupil of your lens with the center rotation axis of your panoramic head.
Next we will align the front back position of the camera on the horizontal arm.  A simple way to do this is to line up two vertical items.  Place one close to camera and the second item further way.  From a center framed position these two items should appear to be stacked on top of each other.  Rotate the camera to the left and right about 20-30 degrees.  When rotated the two items will be in exactly the same position if the camera is aligned.  If the two items do not appear to be "stacked" on top of each other, then simply adjust the forward or back position camera until the items are aligned.

Fisheye Considerations

John Houghton also notes that you need to be aware the entrance pupil for a fisheye is not centered on a single point.  Basically he says that you want to adjust your entrance pupil to correspond with the angle your stitch.  He also notes that this will compromise the accuracy of your zenith and nadir points, but stitching software is usually good enough to fix it.  Check out his site for the full explanation.

Now your probably wondering why bother with both axis when shooting with a fisheye?  You could easily use a simpler rig like the Nodal Ninja 180.  With the NN180 you only align the entrance pupil on one axis and not two.  Wouldn't this be easier on set?

This is true.  But using a panoramic head designed specifically a fisheye limits you to just using a fisheye.  The NN5 allows you do use any lens.  And depending on the lens used you get a significantly higher resolution final panoramic than one created using a fisheye lens.  If you need to capture a high resolution sky or cityscape your in trouble if you only have a fisheye rig.  End of the day if you have the extra coin to buy multiple rigs... go for it!  They happily sell you more than one, but for me one rig that can do both is a bit more cost effective.

Taking your time at this step will result in panoramas that take minutes to stitch together.  And the team back at the office will love you for it!  In fact they may pick you up on their shoulders and parade you around the office, like the hero that you are!

Next time, lets shoot some pictures!

Here is a quick resource list that I came across in my research for this entry.  These guys have put together some very good sites which inspired me while writing this blog entry.

Michel Toby's website
johnpanos.com - Finding the No-Parallax Point
The Nodal Point (This has a very cool laser plotted graph of a sigma 8mm lens's entrance pupil)
Nodal Ninja website
Digital Grin (nodal point tutorial)
The Really Right Stuff
Big Ben's Panoramic Tutorials 
vrphotography.com
The "Grid" tutorial

Sony Announces devlopment of new Single Lens 3d Camera

This looks pretty cool.

Buttery smooth 3d and frame rates up to 240 fps!  Here's the cut and paste...  or the original link.

This technology combines a newly developed optical system for single lens 3D camera which captures the left and right images simultaneously, together with existing high frame rate (HFR) recording technology to realize 240fps 3D filming. Sony will demonstrate a prototype model incorporating this technology at "CEATEC JAPAN 2009", to be held at Makuhari Messe convention center in Chiba city, Japan, from October 6th.
In existing half mirror 3D camera systems with separate lenses for the left and right eyes, the parallax range is adjustable, enabling the depth of the 3D images to be modified. However, when operating the zoom and focus functions of such systems, the sensitivity of the human eye, in particular to differences in the size and rotational movement of dual images, as well as any vertical misalignment or difference in image quality has meant that complex technology has been required to ensure that each camera lens is closely coordinated, and there are no discrepancies in the optical axis, image size, and focus. The introduction of a single lens system resolves any issues that may occur as a result of having different optical characteristics for each eye.

Enlarge

Optical system for single lens 3D camera

Furthermore, by using mirrors in place of shutters, incoming light can now be simultaneously separated into left and right images and recorded as it reaches the parallel light area (the area where diverging light from the point of focus on the subject matter becomes parallel) of the relay lens. The separated left and right images are then processed and recorded with the respective left and right image sensors. As there is no difference in time between when the left and right eye images are captured, it is possible for natural and smooth 3D images to be captured, even of scenes involving rapid movement. Optical tests have shown that a frame rate 240fps represents the limit of human visual perception, and beyond that it becomes difficult to detect differences in terms of blur and "jerkiness" of moving images (where images that were continuous are now seen as a series of distinct snapshots). By developing a 240fps frame rate CMOS image sensor with properties close to the human eye, which is capable of capture natural images of even fast moving subject matter, Sony has succeeded in enhancing the quality of 3D video images.

The combination of Sony's new single lens 3D system and its 240fps high frame rate technology has realized a single lens 3D camera system, based on universal properties of the human eye, which enables natural and smooth 3D images with no accommodation-vergence conflict to be recorded.
Technological Features:
1. New single lens optical system
- Captures left and right images simultaneously to deliver natural and smooth 3D images with no accommodation-vergence conflict.
- Eliminates the need for lens synchronization, ensuring easily accurate control of 3D zoom and focus functions.
- When polarized glasses are not used, viewers with still be able to see natural 2D images, as the disparity of the images for left and right eyes are within the range that human eyes can recognize as a blur.
2. 240fps image capture to realize high quality motion images
- Realizes high quality capture of 3D content including fast-moving subject matter such as sports.
Source: Sony

Cross Polarization Photography and Skin Texures

Hello Everyone,

Here is a good trick for capturing only the diffuse component of a person for the basis for diffuse texture maps in a sub surface scattering shading model.

Bascially what you need to do is filter both your lens and your light source. In this case I am filtering a pair for canon 430 EX speedlights with linear polarizing film. The speedlights are mounted on a custom bracket. The purpose of the bracket is to align speedlights with the camera lens in order to evenly light our subject. (me)

First lets look at the results.


(note: the small amount of reflection/specular light on the right hand image is the uncorrected lights in my kitchen. Ideally you would take your photo in a more controlled setting. Also for this example I did not have 2 flash units available so I just used one directly on the hot shoe of the camera)

Why does it work?
Well when I first learned this trick back in the day.. I was just told "it works". But I wanted to know why so I did some digging. Here is what I've found.

I am paraphrasing The Handbook of Cosmetic Science and Technology, Third Edition. Cross polarization photography lets you differentiate between regular glare and back scattered light. The back scattered light is the complextion within the skin.

Both the camera lens and the flash have a filter placed in front of them. When the orientation of the filters are perpendicular (cross polarization) the regular glare is blocked and only the back scattered light is captured.


But when the filters are parallel only the reflected polarized light passes though the filter to be captured by the camera.

What do I need to take photos like this?

The Basics

• Camera
• Circular Polarizer for your camera
• Linear Polarizing Film (to filter your flash)

More Advanced Setup

• Camera
• Circular Polarizer for your camera
• External Flash units (I used 2)
• Linear Polarizing Film (to filter your flash)
• Flash diffusers (make sure the one you buy fits your flash)
  
• Flash bracket (My good friend and boss Les Ekker helped me make a nifty bracket)
• An external hot shoe extensions
• An adapter to connect more than one flash to your PC sync port
• Extra tripod mounting plate
• some standard "quarter/20" screws (1/4 inch screws with a 20 degree pitch threads). This will fit a standard camera mounting hole.
  

The Flash Bracket


Les had some extra 1/4 aluminum stock laying around so after some carefull planning we drilled a bunch of through holes. 2 hole for the hot shoe adapters. 1 hold for the camera, and the last through hole we threaded and attached a standard tripod mounting plate.

After we did all that... we threw the thing in a vice and gave it a good twist. This was to align the flashes as best as possible with the front of the lens.

presto chango.... hand dual flash bracket! (when I say we...I mean Les, he did most of the work as I drank a beer in his shop.)

Making the flash filter



The flash filter was simple to make. I ordered a sheet of the polarizing film and simply used a sharp exacto knife to cut out a shape that matched the end of the diffuser. We simply taped the film to the end of the diffuser with some common "silver" tape that you can find at the hardware store. I think its generally used to repair dryer hoses. The silver tape will help contain any light leaks from the flash and focus as much light out through the filter.


Shooting Conditions

When shooting you want to control as much as the light as possible and have little or no reflective/specular light sources. (light fixtures, computer monitors, windows etc...)

make sure to focus and have fun.


Now what do I do with these...

Once you've taken a set of photos in each position (perpendicular and parallel) you can do some fancy photoshop action by either inverting or using difference matting techinques to derive a specular only map. These 2 images will take you a long way.


But wait there's more....

This technique works on all kinds of stuff. I've used it to shoot rubber tires, plants, leather and a bunch of other stuff...


here is a link to a page that I came across in my researching for this project.... just wanted to give some credit to naturescapes.com

Here is a flickr gallery that has more pictures of the rig.
enjoy

Andy

HD Lens to 35 mm equivalents

While on a shoot with an HD camera you will almost definetly here the question

"What is the 35mm equivalent of this lens?" Well you can do some fancy math... or use a handy cheat sheet from Panavision. Of course it's only accurate for Panavision lens but it give you a pretty good idea of what your seeing in a 35mm equivalent across the board.


You can down load the full PDF and a simular one here from Panavision's website. This was another gem from Les. He has a photo copy of a photo copy of this document and I did some digging with the help of Johnny B at work and found this on the web.

Enjoy!