Tag Archives: Depth of Field

New tool simplifies focus stacking

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Many times when producing images of small subjects we find that there is insufficient Depth of Field (or depth of Focus) to render the entire subject sharply from front to back. Insufficient Depth of Field (DoF) is cause by three factors:

First, we understand that, in addition to exposure,  aperture controls DoF. As we increase the F number we add DoF. However we may not be able to make a good exposure with a big F number like F22.

Another factor is that as we increase the focal length of our lens, the DoF becomes smaller. We could select a shorter lens, but that changes perspective and ability to focus close in the case of a macro lens.

The final consideration is that when the lens is moved closer, the DoF also becomes smaller. Thus we are our best enemy and must deal with self-imposed photographic criteria.

Therefore we have learned to use focus stacking to solve this problem. This requires a series of often many images, each made at a different point of focus from front-to-back. The images are blended into on in the computer using specialized software. The image of the bee (below) is an example of a stacked composite of 50 blended images.

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The several images are captured using different points of focus. Some lenses change magnification as the focus is changes, creating alignment problems. The better approach requires moving the camera a measured increment between shots. A geared focusing rail (below) or an automated programmed focusing rail are specialized tools for changing the focal point without compromising image size.

FocusRailDuo-Sm

Another system uses a rail incorporated into a bellows system to change focus but not scale, as pictured below. There are several choices from several manufacturers to accomplish this movement process.

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Now comes the new tool on the market- The Helicon FB Tube. This new idea comes from the producers of Helicon Focus, the industry leader in image stacking software. Essentially it is an extension tube with integrated electronic micro-controller designed to enable automated focus bracketing in single or continuous shooting modes. The measured tube length is 13mm and adds somewhat to the magnification of the lens dependent upon the focal length. Mounted on the camera in the same way as a usual macro extension tube, Helicon FB Tube automatically shifts the focus by one step with each shot thus producing a stack of images of unlimited length that can be rendered into a fully-focused image.

Helicon FB Tube needs no additional hardware apart from conventional cameras and lenses. Helicon FB Tube has no optics and does not affect image quality. Helicon FB Tube settings are configured through an additional application for Android or iOS. The set contains: Helicon FB Tube with IR Receiver and LED Indicator; Front and Rear Caps; IR Transmitter – connects audio port of a smartphone and Extension cable for smartphone and IR Transmitter.

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The unit has been tested and found compatible with a wide number of camera models and lens. Helicon FB Tube is available with mounts for Nikon and Canon cameras and AF lenses with built-in motor.

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I tested the image focusing ability of the FB Tube making 15 focus step images of the acorns below using a step factor of 70. The camera was a Nikon D800 with the FB Tube and 105mm F2.8 Micro Nikkor. Selected aperture was F5.6. Electronic flash in TTL Mode within a softbox provided consistent light.

To set up the FB Tube a couple of simple settings are made on the smartphone device, including lens focal length, crop factor, aperture and step size. this was relatively straight-forward on my iPhone using the available ap:

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IMG_3537  IMG_3539

The phone then transmitted the data to the FB Tube via an IR emitter plugged into the phone audio jack and aimed at the tubes receiver. as shown below.

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To get started, the first focal point was focused manually at 3.0 CM on the rule. The rest of the images in the series were focused automatically by the FB Tube. Three of those images are shown below -the first, middle, and last- of the 15 image sequence.

Acorn Stack-01FP Acorn Stack-07FP Acorn Stack-15FP

The fifteen images were selected in the computer and rendered in Helicon Focus
Method B (depth map) in a normal manner, rendering sharp focus from front to back. Final adjustments for tone, color and sharpening was completed in Photoshop CC.

Acorn Stack Complete

There are several procedures to make images for stacking. Moving the camera is simple and inexpensive. A manual rail is a bit of an expense, Fully automated, servo motor driven rails and associated accessories are often more than $600. In comparison, the Helicon FB Tube costs $200.

Copyright © Brian Loflin 2017. All rights reserved.

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Which lens do you use?

 

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Nikon D800, Nikkor 105 mm F 2.8 lens.

We are told that the key to making a good composition is to pick the “right” lens and decide where to place it and the camera in relation to the subject.

It quite true that you can fill the frame with a portrait and make the head size the same dimension in the frame regardless of the lens focal length used. Even though this is true, there may be a better choice for selecting one focal length over another. Let’s evaluate a few images all made at the same spot:

20mm-8356-LG-Sm    60mm-8361-1-LG-Sm

This image on the left is made with a 20mm Wide Angle lens. It is quite obvious the face is distorted by the wide angle. In addition, the lens was just over one foot from this lady’s nose- quite uncomfortable for the subject.

This image on the right is made with a “portrait” lens, a fast 60mm F2.8 prime. It still is a bit wide and the lens to subject distance is still quite uncomfortable. With these two lenses the background is more defined that desirable.

85mm-8366-1-LG-Sm     105mm-8376-1-LG-Sm

The left image (above) is made with a fast 85 mm, F1.8 prime. It is beginning to look better. There is more comfort with the subject. Yet, the background is still somewhat more defined than desired.

The image on the right is a prime 105 mm F 2.8 lens. The working distance is very comfortable, the background becoming soft and there is little distortion of the subject’s face.

The next pair of images (below) are made with focal lengths in the telephoto range. They look much better than those above.

135mm-8386-LG-Sm    200mm-8391-LG-Sm
Camera: Nikon D800. Nikkor lenses: 20mm F2.8, 60mm F2.8, 85mm F1.8, 135mm F2.8, and 70-200 F2.8 zoom.

The left image is a 135mm F2.8 prime and the right, a 200mm F2.8 zoom . Both of these lenses produced good frame-filling head shots with pleasing facial features and nicely softened backgrounds. All images are made on a full frame Nikon D800 digital SLR at an aperture of F3.5.

So, in my book you can’t beat the image quality and feeling with the two telephoto lenses. For years and years, the choice for portraits on full frame cameras has been the 105 mm lens, regardless of whether shooting on film or in digital. We can now understand why.

So, the concept of a “portrait” lens for digital is a little misleading. The 50mm F1.4 is and always has been a great choice for editorial portraiture. This is because of the ability to better manage the Depth of Field and to tell a story, not for its focal length. For many this lens is simply just too short to use for pleasing head shots.

However, with a full frame 50mm lens on a crop sensor camera, the 50mm acts much more like a 75mm in its angle of view and  because you may be a bit further back.

Still it’s hard to beat the longer lenses. The advantages are many. You may fill the frame further from the subject, reducing distortion and improving a soft bokeh and shallow Depth of Field in the background. The narrow angle of view allows a small  “slice of life” to be made, eliminating many background distractions. Additionally, if you are shooting with lights or lighting modifiers, you have more working room if further back.

Copyright © 2016 Brian Loflin. All rights reserved.

 

 

 

 

 

 

 

Showoff your Subject- Manage the Background

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Northern Cardinal female, Nikon D800, Nikkor 80-200 F2.8 lens, 1.7x teleconverter.

 

To achieve the very best from every photographic composition it is very important to assure the subject stands out in the frame. To do this you must manage the background.

There are three basic ways to manage the background: Separate the subject from the background by using a very small Depth of Field; Use contrasting tone values; and Use complementary colors. The more of these effects that are used in a photograph, the more successful that composition becomes.

The first method is to set off or separate the subject from the background by muting all background distractions by using a minimum amount of Depth of Field  (or depth of focus).  To do this effectively first focus carefully on the subject and use a small F number aperture. The small F numbers provide a very small amount of the scene, both in front of and behind the point of focus that is in acceptable focus.

It is not reasonable to simply use the smallest F number provided by the lens. It is important to have enough DoF to cover the subject in its entirety. Larger subjects require a bit larger DoF.

Here is a comparison. The first image below is of the branch where the cardinal was perched. It was made with a lens at 340mm and at F29. The second image was made at F4.8. The comparison is quite evident. It is also important to remember that the DoF gets smaller as the lens focal length gets longer.

_BKL5594-1-SmDeep and distracting background above. Few distractions and smooth, pastel background below.

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In the next post we will review the second technique, use of contrasting tone values.

Copyright © 2016 Brian Loflin. All rights reserved.