Verified Photomontage

Field Photography

Field Equipment - Photographic Digital SLR Camera with standard lens (full frame) A second camera is useful (compact will do) Tripod with 3-way head A 2-axis bubble level (hot-shoe mounted) Telephoto lens Additional kit for panoramas Levelling base for tripod head Panoramic head (2 sliding plates)

Field Equipment - Survey Maps and plans Compass Hand-held GPS (distant viewpoints) 5m and 30m tape Ranging poles (if no visible control points) Survey marker paint or pegs/nails (for survey) Notepad and pen Watch (or check camera time) A surveyor with survey instruments

The Camera Digital SLR with a standard lens.

Most DSLRs use a cropped sensor – this changes the focal length of any lens used.

Some clients or authorities may insist on the use of a full-frame* camera.

* A full-frame camera is one in which the sensor size is 36mm x 24mm, the same as the traditional frame size on 35mm film cameras.

Cropped sensor cameras

Cropped sensor cameras may be used provided they can be matched with a suitable standard lens.

For example, Canon* cameras such as the 7D and 70D use sensors smaller than full-frame that give a X1.6 magnification factor.

A standard 50mm lens would result in images with a 80mm focal length (50 x 1.6) if used with a cropped sensor camera.

* Other manufacturers may use different sensor sizes

Sensor sizes

Cropped sensors are smaller than full-frame sensors and the effect on the image is an apparent magnification.

Lenses for cropped sensor cameras

A lens must be used with cropped sensor cameras that will give the equivalent of a standard focal length.

For example, a 30mm lens on a cropped sensor camera would result in an image with the equivalent of a 48mm focal length (30 x 1.6) on a full-frame camera.

This is within the standard focal length range of (45-55mm).

Which Camera? A full-frame DSLR camera is recommended for verified photomontage work and there are a number of suitable models on the market, e.g. The Canon 5D and 6D or the Nikon D600.

Never use a compact camera or phone to take photographs for verified photomontage because you don’t know what focal length is being used.

The Lens

Choosing the correct lens for verified photomontage work is as important as using the correct camera.

It’s not a good idea to use the basic kit lens supplied with your camera.

You should consider a number of points…

Focal Length

Wide angle < 45mm Standard = 45mm to 55mm Telephoto > 55mm

Standard lenses are so-called because they give an image that is equivalent to what the human eye sees – a field of view of 40 degrees of arc.

Understanding Camera Lenses

Zoom or Prime Lens?

A zoom lens has a variable focal length. A prime lens has a fixed focal length.

Zoom lenses are best avoided because:

1. It’s often impossible to be precise about the focal length.

2. Focal length may vary slightly between frames.

3. Image quality may not be as good as the equivalent prime lens.

Which Lens?

The best lens for photomontage work is a good quality prime lens with a fixed focal length of 50mm for full-frame sensor cameras or an equivalent standard focal length for cropped-sensor cameras.

All lenses have some optical distortion but macro lenses tend to have the least, so a 50mm macro lens may give the best results.

Aperture

The aperture setting controls the amount of light entering the lens using an iris.

The aperture setting is known as the f-stop and is expressed as a number such as f/2.8

Most lenses have a sweet spot* at around f/8

Aperture also controls the depth of field…

* The sweet spot is the aperture which gives the best (sharpest) image quality for any given lens.

Depth of Field

Depth of Field Shallow Deep

Depth of field refers to that part of the line of sight that is in focus.

Small f-numbers result in a shallow depth of field and large f-numbers result in a deeper depth of field.

Depth of Field

Depth of Field Shallow Deep

f / 2.8

f / 8

f / 22

Aperture changes Depth of Field

Depth of Field Shallow Deep

The aperture setting changes the depth of field.

Depth of field causes a change in the image.

Therefore, the aperture should always be fixed when taking photographs for photomontages.

Use Aperture Priority Mode

Depth of Field Shallow Deep

When taking photographs, set the camera mode to Aperture Priority (Av).

The correct aperture is a balance between maximum depth of field and staying close to the sweet spot (often f/11).

Shutter Speed

Shutter speed controls how much light hits the sensor or film plane.

Since it does not affect the image (as aperture does), it doesn’t matter what speed is used unless the subject is fast-moving.

Any speed will do

Since the camera is always on a tripod, even slow shutter speeds (slower than 1/60th of a second) can be used without causing camera shake, although it is advisable to use a cable release.

Sensor sensitivity

Sensor sensitivity is the third of the “three pillars” of photography, the other 2 being aperture and shutter speed.

Sensitivity is known as ISO and is expressed as a number, the higher the number, the higher the sensitivity.

Typically, a modern camera will have an ISO range of 100 to 25600.

Sensitivity vs. Image Quality

Greater sensitivity to light means that photographs can be taken when light levels are low, which is a good thing.

But, at higher sensitivity levels, the resulting image is subject to increasing “noise”.

Noise will reduce image quality and lose fine detail; so there is always a trade-off.

ISO

ISO 100 ISO 25600

Which ISO is best?

For photomontage work, we want the best image quality your camera can achieve.

Therefore, you should always use the camera’s base ISO. This is usually the lowest value, typically ISO100.

This value should be set explicitly because the default on most cameras is Auto, meaning the camera can decide.

Focus

All modern cameras use autofocus to ensure pictures are correctly focussed.

However, even small changes in focus can change the image.

The framing of the two images on the right is the same but the result of different focus is clear.

Use Manual Focus

Do not use autofocus – set your lens to manual focus.

Focus manually on the horizon or some intermediate point, depending on subject.

Maximizing depth of field

As a general rule of thumb, you can maximize depth of field by focussing about one third of the way to the horizon.

This will ensure that as much of the image as possible is in focus, from foreground to horizon.

If your camera has depth of field preview, you can do a visual check.

The Tripod

The tripod should be sturdy enough not to cause camera shake but light enough to be easily portable.

It should be able to support a camera at eye-level.

There are many suitable tripods available such as the Manfrotto 055XB.

The Tripod Head

For single-frame photomontages, a simple 3-way head is all that’s required.

It is convenient to use a head with a quick-release plate so that the camera can easily be mounted and removed such as the Manfrotto 808RC4.

Heads for Panoramic Views

A more complex head arrangement is required if the views are panoramic.

1. The plane of rotation of the 3-way head must be horizontal, this requires a levelling base fitted below it.

2. The effects of parallax error must be eliminated and that requires an arrangement of sliding plates above the 3-way head so that the nodal point of the lens can be positioned on the axis or rotation.

Levelling Base

The levelling base sits between the tripod and the levelling head.

Once the tripod is setup, the levelling base is adjusted so that the plane of rotation is perfectly horizontal.

This will eliminate stepping in the panorama.

The levelling base shown here is the Manfrotto 338.

Panoramic Heads

Dedicated panoramic heads are available but as we are only concerned with horizontal panoramas, a simple arrangement of 2 sliding plates is all we need.

One plate for forward-backward movement and one for left-right movement.

Sliding Plates

I use a Manfrotto 454 micro-positioning plate for forward-backward adjustment mounted on a 357 sliding plate for left-to right adjustment.

The movement facilitated by this plate combination allows the nodal point of the lens to be positioned on the axis of rotation.

The Manfrotto 454 micro-positioning plate.

Panoramic Photographs

A panoramic image is constructed from two or more images taken with a standard lens and manually stitched together in Photoshop. Auto-stitching is not recommended because it introduces distortion.

Parallax Error

Parallax Error

Light rays travel unequal distances to the image plane as the camera rotates, causing parallax error.

The nodal point of a lens is a point of singularity through which all light rays pass. Rotating the camera about the nodal point eliminates parallax error.

Parallax Corrected

Parallax Corrected

Camera support with panoramic head

Panoramic head setup and front to back positioning

Panoramic head setup and side to side positioning

Planning

Weather conditions

Time of day (position of sun)

Eastern viewpoints shot in the morning

Western viewpoints shot in the afternoon

Information Recorded

Camera location, grid reference or triangulated measurements or survey quality GPS

Ground level AOD (if no GPS available)

Camera height above ground (centre of lens)

Photo of tripod in position (a second camera)

Information Recorded

Control point locations (3 minimum)

Control point photographs (telephoto lens)

Bearing of view (with compass)

Time of day (rendered shadows)

Camera viewpoints should be clearly marked using a surveyors nail, wooden peg or marker paint.

A photographic record of tripod positions is made so that the same locations can be found again in the future. This is a fall-back in case survey markers are lost or not possible.

Survey of Viewpoints

GPS Survey of Viewpoints

Viewpoint surveyed using a Leica SmartRover with an accuracy of sub 20mm. This uses ground station correction in addition to satellites for greater accuracy.

Survey of Control Points

GPS Baseline A total station is used to survey control points for each viewpoint. Before that can be done, a baseline (around 100m) must be set up using an additional GPS point. Using this method, control points up to 1km from the viewpoint may be fixed.

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The 3D Model

A 3D model of the proposal is built in AutoCAD. A visual marker is added for each viewpoint and a camera perspective constructed. Control point locations are indicated with a visual marker. Perspective views of proposed buildings and control points are printed to EPS. EPS file is then rasterised in Photoshop and matched with the photograph.

Building the Photomontage

existing scene background mask building render layer mask render detail yr 1 planting yr 15 planting

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