The extremely high resolution of the Better Light scanning backs can make some stunning images. Details which cannot be resolved with lower resolution cameras leap out at the viewer. The penalty for all this extreme detail is a much shallower depth of field in the image.

In the past this meant the photographer had to move the camera further from the subject, change lenses or stop down to get more depth of field. These adjustments can often result in the necessary exposure values going out of the allowable range for the scanning back, resolutions lower than desired for the final image, or exceeding the diffraction limits of the lens.

This has now changed with the advent of extended focus programs. When fed a set of images shot at different focal points, an extended focus program will combine the in-focus parts of each image together to produce a single image with an increased depth of field.

How They Work
To make an extended focus image, a sequence of images, called an “image stack”, is created in one of two ways; fixed or variable focus.

Fixed focus programs require the images to be created by focusing on one part of the subject, then moving the entire camera forward or backward to place the focus plane at the next part of the subject. Moving the camera with a set focus will maintain the magnification but it can be more difficult to achieve, depending on the camera used for the imaging.

Variable focus imaging means that the camera is fixed in position with each image created by changing the camera’s focal point to move the focus plane through the object. With this method, the magnification is changing as the focus point is moved.

A Web search yields several extended focus processing programs, but few are available for both Mac and Windows. Two that are cross-platform are Focus Extender (www.reindeergraphics.com) and Helicon Focus (www.heliconsoft.com).

Focus Extender
Originally designed for processing extremely shallow focus microscope images with fixed focus images, this is a Photoshop plug-in module with versions for both Mac and Windows. It requires fixed focus image stacks only with all the images aligned to each other, the way a microscope works. This means that the sizes of the objects and their positions in the image must not change, only the focus changes. These conditions are extremely difficult to achieve for product shots and even for copy shots it is very hard to precisely center the object on the copy board. For these reasons, fixed focus only programs, such as Focus Extender, are not recommended.

Helicon Focus
Working with both fixed and variable focus image stacks, Helicon Focus is a stand-alone program. It can take 8-bit or 16-bit per channel images, runs on both Mac and Windows computers, and has the ability to work with multiple processors to make everything crunch together faster, depending on the license you purchase

The bad news is that Helicon Focus cannot process images larger than about 400 MB in size. The actual size is somewhat difficult to pin down, but it is somewhere between 300 to 400 MB. So those photographers that always shoot their Super 8K Better Light scanning backs at 150% resolution, 16-bits per channel, will have to scale back the image size in order to use Helicon Focus.

If you can live with these restrictions, Helicon Focus is a great tool to add to your imaging tool chest.

To make the image stack, begin by setting up the shot and focusing on the front-most scene item to be in focus. Take the image, then move the focus toward the back of the scene. It is best to have the in-focus area of each image overlap with the in-focus area from the previous image. Continue moving the in-focus area back through the scene until the entire scene has been captured. The image stack is now ready for Helicon Focus.

Start Helicon Focus then select the image stack. Click the “Run” button and sit back. As it processes each image a preview of the result is shown in the processing window. The effect as you watch is that the depth of focus grows from the front toward the back.

If you have a camera with a scale indicating the focus setting, such as found on some rail cameras, finding the front and back focus positions then moving the focus a set number of scale divisions can make this process easier.

Also, using ViewFinder’s “Auto Naming” feature will make it easy to name each shot and keep track of where you are in the sequence as you make the images.

EXAMPLE IMAGES:

Watch
This subject is a watch with the clasp locked so the watch was self-supporting. This resulted in about a 2.5 inch distance from the watch face to the clasp. To make the image the camera was focused on the front face, then the clasp and a reading from the camera’s focusing scale was noted for each focus point. Six images were taken from the watch face to the clasp, then combined in Helicon Focus to produce the extended focus image seen below.

First Image – Focus on front of face		Sixth Image – Focus at back of band		Resulting image with Helicon processing Click here or on image for enlarged view.

Photographic Items
This extended focus image was created from 16 images. The front lens standard was tilted forward slightly to align the plane of focus better to the plane of the objects. In each image the depth of field was around 2 inches. When the entire set was stitched together the resulting image has about a 16 inch depth of field.

Image 1 of series – focus at closest point at base of loupe		Image 16 of series – focus at farthest point on light meter

Result of Helicon processing of all 16 images – precise focus front to rear

Map
To simulate a large, flat object, such as would be encountered for a fine art reproduction, a map was imaged so that when focused on the center the corners would be out of focus. The map was then re-imaged with the focus at the corners and the center out of focus. When combined by Helicon Focus, the resulting image is sharp from corner to corner.

	CENTER-FOCUSED IMAGE		CORNER-FOCUSED IMAGE		EXTENDED-FOCUS IMAGE
UPPER LEFT
CENTER
RESULT