Experimenting with Tele Stereo Photography3d-con.com/2018/files/THEMELIS-TELE-3D.pdf ·...

Experimenting with

Tele Stereo Photography

By George Themelis

Tele what ???

Tele = From a distance (far away)

telephone, telegraph, television, telescope, telekinesis

3D Photography

from a distance

Tele Stereo - Why?

1. There is a physical barrier

2. Subject feels uncomfortable / threatened

3. Photographer feels threatened

4. You want the subject to be unaware that it’s being photographed

5. Special effects (perspective compression)

6. Other advantages (reduced DOF in close-ups)

7. Photographer’s choice

Two Types of Telestereo

1 - Using wide angle/normal lenses

Hyper tele stereo photography, aka hyperstereo

2 - Using long FL (telephoto) lenses

Close-up tele stereo photography

These have different challenges

Examples

Using wide angle/normal lenses

Hyper tele stereo photography, aka hyperstereo

Example of “Compressed Perspective” http://www.dailymail.co.uk/news/article-3756633/

Spectacular-photograph-blood-red-moon-rising-Manhattan-looks-like-Mars-hovering-Big-Apple.html

Hyperstereo Subjects

• Single camera hypers from a plane (or boat or other moving platform)

• Landscape hyperstereos (Grand Canyon, etc)

• High perspective cityscapes (from a building, etc.)

• Fireworks

Large Stereo Base ~ 1/30 x (near) Object distance

Examples

Using telephoto lenses

Close-up tele stereo photography

Close-up Tele Subjects

• Wildlife, animals, birds, animal close-ups, zoo

• Other nature close-ups (flowers, etc)

• People, portraits, street photography

• Long distance action (sports, shows, etc)

• Compressed perspective

Think: Binoculars

Stereo Base can be smaller, alignment is critical

• What and Why?

• Two types of telestereo

• Theory and metrics of close-up Telestereo

• Focal Length (F) & equivalent focal length

• Magnification (M) + ways to increase it

• Stereo Base (B) & Relationship between F and B

• Equipment

• Single camera

• Twin cameras

Outline

Focal Length

From: http://www.digital-photography-student.com/wp-content/uploads/2009/11/Focal_Length_Diag.png

Magnification

Size of Image - Where?

• On film / sensor

• On camera’s screen

• On computer display

• In projection

Technically, on film/sensor. A macro lens capable of 1x magnification, produces an image on the sensor that has the same size as the object.

A practical solution around this ambiguity is to assume a “full frame” (24x36mm) sensor.

Magnification

Magnification = Size of Image / Size of Object

24mm

M = 24mm / 240mm = 1/10

Magnification

Magnification = Focal Length / Distance

Magnification

Two ways to increase the magnification

Increase the focal length

Reduce the distance (get closer)

Please Note:

• Increasing the focal length enlarges the image. The focal length acts as a scaling factor. Everything (foreground and background) becomes equally larger.

• Enlargement after taking the picture also acts as a scaling factor (everything becomes equally larger). It has the same effect as using a longer focal length lens in the first place. In most cases you cannot tell if the magnified image that you see is the result of using a long focal length lens or cropping and enlarging an image.

• Reducing the distance or getting closer. The distance affects the closer objects more than the far objects. So it affects the perspective (ratio of size of near vs. far objects).

Three ways to increase the magnification

1. Increase the focal length

2. Crop and enlarge

3. Reduce the distance (get closer)

Types of Cropping:

From: https://photographylife.com/what-is-crop-factor

1) In camera 2) Using software 3)

Digital Format Sensor

(mm x mm) Crop Factor

Full frame eq. of 300mm lens

Full Frame camera 36 x 24 1.0 300 mm

Samsung NX (APS-C) 23.5 x 15.7 1.5 450 mm

Micro 4/3 (Panasonic) 17.3 x 13 2.0 600 mm

No matter if the cropping takes place inside the camera or later, using software, the bottom line is that the final image appears as if it was taken with a lens of a certain (longer) “equivalent” focal length

Crop Factor

Q: What Focal Length lens produces an image of the moon that fills the frame?

24mm

M = Image of Moon / Size of Moon M = F / I (distance of moon) Size of Moon = 2,100M Distance of Moon = 239,000M 24mm / 2100M = F / 239000M

F ~ 2700 mm

Questions:

1. What focal length lens took this picture?

2. Distance of the photographer from the buildings?

3. Bonus: For 3D, what stereo base should you use?

1. ~ 900mm

2. ~ 28 miles

2D Photography

Metric/ Variable

Size S’=SF/I

Perspective dS=dI/I

Focal Length

F + Distance

1/ I + +

3D Photography

Metric/ Variable

Size S’=SF/I

Perspective dS=dI/I

Depth P=FB/I

Focal Length

F + + Distance

1/ I + + + Stereo Base

B +

Stereoscopic Deviation

aka “Parallax”

Small differences (horizontal displacements) between the right and left picture, which, when fused by the brain, provide a sense of depth

P

The Challenge in 3D photography Keep stereoscopic deviation with certain limits

You can measure P easily by

overlapping the two images

(using StereoPhoto Maker) and

measuring their displacement

in pixels. It’s better to express it

as a ratio.

• If the distance (I) is large (telestereo) and the focal length (F) normal or small, then the stereo base must increase (Hyperstereo)

• But if the focal length is also large, then it’s unclear if the

stereo base should increase or can remain small (close-up telestereo). It all depends on the distances of near and far objects

Stereoscopic Deviation

Stereoscopic Deviation

P = M B

P = M (B/I) t

Constant Magnification (you increase the focal length and step back so the magnification remains the same): The stereo base should remain constant.

For close-ups, macro (there is no infinity, subject has limited depth, t): You should increase the stereo base in proportion to the distance.

P = F B / I Distances do not change: As you increase the focal length, you should reduce the stereo base proportionally.

Question: If I increase the focal length, what should I do with stereo base, increase it, keep it the same, or decrease it? It depends!

In practical terms, when using long focal lengths to take close-ups, the stereo base can increase a bit or remain constant. It does not have to be too large. That’s why binoculars work.

Type of picture Recommended B/I

Distant Stereo ~ 1/30

Macro ~ 1/10

Close-Up ~ 1/20

3D Similarity Principle You can take a close-up picture with longer lenses from a distance or with shorter lenses closer

Pictures that have the same:

• Magnification (F/I)

• Convergence ratio (B/I)

Look surprisingly similar provided that the background is blocked

Camera Equipment

1. Stereo camera + cropping

2. 2D camera(s) + long lens

Going through the 2D camera route, you can use one camera and shift (cha-cha) to photograph subjects that don’t move, or use two cameras synchronized for moving subjects

Stereo Camera

A standard stereo camera ( B~ 50-75mm ) can be used to take close-ups

Stay back, zoom in and crop later

2D Camera

1. Camera w/ inter-changeable lenses & a long lens

2. Camera w/fixed lens with wide zoom range (superzoom)

Samsung NX500 camera with a vintage 300mm

mirror lens (600mm equivalent)

Panasonic FZ2500 “bridge” camera with 24-

480mm (equivalent FL) built-in lens

Camera w/interchangeable lenses Sources for lenses:

Buy new or used (ebay, etc.) Three types of lenses:

1. Camera manufacturer (OEM)

2. Third Party Lenses (Generic)

3. Vintage / Legacy Lenses

Buying Used /Vintage / Legacy Lenses

Older lenses often have issues with: • Fungus • Haze • Element separation • Excessive “dust”

Always inspect a lens using a flashlight

Make sure that you can return the lens. Ask before buying about the optical condition of the lens.

Adapting Vintage / Legacy Lenses Vintage lenses can be adapted to many digital cameras using simple and inexpensive adapters:

These are hollow tubes serving two purposes: 1) Adapt the lens mount to camera mount 2) Adjust for infinity focus

No communication of the lens with the camera: 1) Manual Focus, 2) Manual setting of f-stops

Mirror • Long FL & compact size

• They have a fixed aperture

• They have a unique Bokeh

• Lower contrast

• Relatively inexpensive

Most common mirror lens:

500mm f8 ~$50 (Generic)

~$100-$200+ (Name brand)

~$500+ (premium)

“Bridge” Cameras

• Bridge cameras bridge the gap between expensive single-lens reflex digital (DSLR) cameras and point-and-shoot cameras

• They are larger than point-and-shoot

cameras (they look similar to DSLR cameras - see the Panasonic FZ2500)

• They have smaller sensors • They have fixed (not interchangeable)

lenses • They have wide zoom range (aka

“superzoom cameras” - travel or bridge)

Why use Bridge Cameras?

• Very long zoom range

• Simplicity of fixed lens & good matching of focal lengths

• Excellent image stabilization (can shoot hand-held at 1/100s @ 500mm FL)

• Good camera build & macro capabilities

• Disadvantage: Small sensor

Maximum Zoom - FZ2500

• Extended Optical Zoom: When using a smaller image size, the zoom can be extended without any deterioration of the image quality. When the image size is cut in half, the zoom increases by √2

• Intelligent Zoom: According to Panasonic, intelligent zoom can extend the focal length by 2x with minimal image deterioration. I am not sure how this works.

• Digital Zoom: The camera crops and enlarges the image. With digital zoom it is possible to extend the focal length by 4x, but the image quality deteriorates.

In theory only the optical focal length matters. Any operation to increase this is done digitally (by cropping or cropping & enlarging) and this can be done either by the camera, or (better) later by the user and software.

In practice, there are advantages in being able to extend the focal length while taking the picture. It allows the photographer to see, frame, focus, expose the subject better.

Image Size (MP)

Extended Intelligent Digital

20 480 960 1920

10 677 1354 2707

5 960 1920 2840

Major Issue when using Long FL Lenses

Alignment

From: https://www.bhphotovideo.com/explora/

photography/tips-and-solutions/how-test-your-lens

Vertical Alignment

• If the center of gravity of the lens is in the front of the bar, I control the vertical alignment by adjusting the rail mounting screw.

• Having a grid on the camera

helps align the images.

Adjusting Vertical Alignment

Area of overlap when the lenses

are pointed parallel.

Horizontal Alignment

If the cameras are pointed parallel, there will be partial Image Loss (= M x B)

The lenses must converge!

When using Long FL Lenses

Focus is Critical

• Auto Focus: Either converge the cameras accurately (so they point to the same object at the center) or adjust the focus area so the cameras focus at the same object (which can be off the center)

• Manual Focus: Lenses must be focused individually.

Focusing is critical because of very narrow DOF. It helps to enlarge the image area.

Twin Panasonic FZ2500 cameras

Testing the twin camera rig in the field

Disaster

• Rig heavy to carry and not easy to set up quickly

• Vertical alignment not working when cameras are pointing up

• Convergence hard to adjust in lower light

• Result: Maybe one decent pair

Bottom-to-Bottom configuration

Jasper Twin Vertical camera Mount

• Portable - can be held with a grip or monopod • Can be aligned vertically well and remain aligned • Easy to adjust convergence (horizontal) control • Smaller stereo base (~100mm/4” for my cameras)

• Disadvantages: Fixed spacing, vertical orientation

https://www.stereoscopy.com/jasper/vertical-toe-in.html

5472

3648

3:2

3648

2736

4:3

Cropping of Panasonic FZ2500 Images

1. Switch from vertical to Horizontal: 5472 pixels → 3648 = 1.5x enlargement

2. Enlarge 2736 pixels → 1080 = 2.5x enlargement

1.5 x 2.5 = 3.75x (maximum enlargement factor) EF = 480mm x 1.5 = 720mm x 2.5 = 1800mm

1.5x - 3.75x

While maintaining HD resolution

How close can I get?

Type of picture Recommended B/I

Distant Stereo ~ 1/30

Macro ~ 1/10

Close-Up ~ 1/20

B = 100mm

I = 3 m

I = 2 m

I = 1 m

Two issues with telestereo

Size distortion

(due to compressed perspective)

Depth distortion

(a.k.a. Cardboard Cutout)

Issue with telestereo

Size distortion (due to compressed perspective)

Problem: Farther objects appears to be larger (and near objects appear to be smaller).

Problem with subjects of known size (people) or sensitive subjects (portraits)

Remedy: Reduce the stereo base

Issue with telestereo

Depth distortion (a.k.a. Cardboard Cutout)

Problem: Objects appear to be cardboard cutouts, i.e. they lack depth within. Problem is apparent when depth is discontinuous.

Remedy: Increase the stereo base. Compose differently.

• 3D photography from a distance

• Why? you cannot come closer (or for a reason)

• Two types of telestereo - Normal (hyperstereo) and close-up (using telephoto lenses)

• Variables and their relationship - Pictures that have the same magnification (M = F/I) and same convergence ratio (C = B/I) appear very similar (same object size + same depth)

• Equipment - 3D camera (zoom and crop), 2D cameras and a long lens or built-in long lens

• Alignment (and focus) is critical when using twin cameras

• Perspective distortion and cardboarding can be a problem with telestereo

Summary - Telestereo

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