Increasing Depth of Field of Micro/Macro Lens with Helicon Software

 

The most inventive machine on the planet is the human mind. It never stops being curious and never stops coming up with creative solutions to problems. So it should not come as a surprise that technology, in the form of a software product called "Helicon Focus Lite" (www.heliconsoft.com), has addressed and mainly solved the shallow depth of field problem when using a macro/micro lens at small or moderate reproduction ratios (see below). Here the terms micro or macro mean the same type of lens, those used in close-up photography. To give you some idea just how marvelous this piece of software is, letís look at some flower petals which are of low to moderate contrast and very difficult, at least for me, to even manually focus sharply.

 

  

If Image B does not impress you, think about this. At a focal distance of 16 inches, the depth of field of the Nikkor 105mm is about 0.1875 (3/16) inches (~5mm). From front to back the petals span 1.5 inches and thatís why just about everything in Image A, except the outer edge of one petal, is out of focus whereas most of Image B is in focus; look at the edges and you will see what I mean. The results are not 100% perfect, but I never look a ďgift horse in the mouthĒ. OK, I hope you are excited so letís get into some technical jargon so you can understand a little about the limitations of sharpness for a macro/micro lens.

 

The depth of field (DOF) depends on the aperture setting and focusing distance. With zoom lenses it is still essentially the case but changes in the focal length give different magnifications which make it appear that the depth of field has changed - it stays virtually constant as you zoom in and out. Now a macro-lens has very small depth of field at focal distances of around 3 feet (~1m) or less. At focal distances of 1 foot or less (<= 0.3m), the depth of field is essentially in fractions of an inch (0-5 mm) or close to zero from f/4 to f/22.. All this translates into the simple fact that when photographing close-up of a non-planer object (something other than a flat surface, say a flower or insect), those portions of the image closer or further away from the point where the lens focused will be out of focus. I like the creative possibilities of out-of-focus images but I also like the idea of subject matter being sharp and crisp when I want it to be sharp and crisp. Yes, maybe I am spoiled but now everyone can be spoiled using Focus Lite. Well, letís turn to the depth of field for 105 Nikkor to see what we were up against. Note I used the past tense here.

 

Depth of Field Charts for 105 Micro Nikkor; 

To demonstrate this easy-to-use software, we will employ a Nikkor 105mm f/2.8 Macro lens. LetĎs get a view of just how limited the depth of field can be then apply the Focus Lite software.  These charts are from actual data from that lens:

 

 

Now that we have briefly explored depth of field and what a typical macro/micro lens has for depth of field values at various focusing distances, letís turn to setting up the equipment and see how to use Focus Lite.

 

 

How To Take Images and How to Use Helicon Focus Lite

 

Camera Setup and Sequencing Images:

 

1.                Camera must be on a sturdy tripod with a cable release. The camera must not move during image taking with Focus Lite.

2.                TURN OFF THE  Auto-focus; focus manually.

3.               Focus on the portion of the object that appears closest to the camera.  If you can focus on an edge or where there is good, but narrow, contrast separation (light/dark, dark/light), it will help you focus more accurately. For me this is the hardest part with todayís DSLR cameras, focusing without using the cameraís auto-focus capability.

4.                Once in focus, trip the shutter then refocus slightly further into the object and snap the shutter again. Repeat this process as you step through the object from front to back.

 

Recommendations:       

A.     Use an aperture of f/14 or smaller, even f/22, but be careful at very low apertures; increased diffraction of light at very low aperture reduces sharpness.

B.     When stepping through the object, try to maintain some level of overlap between sections focused on. Do not blur out completely one adjacent section from the next section but keep partial sharpness in the overlap between sections. This is important to do otherwise the software wonít perform well. By partial sharpness is meant, not fully blurred out.

C.     Donít worry about taking too many shots; worry about too few. The number of shots depends on the f/value and the depth of field, which, in turn, depends on the focal distance used. The smaller the focal distance and hence the depth of field, the more shots are needed. In some cases, 2 or 3 shots at say f/16 or f/18 are needed and others times, at closer focal distances, usually at 1.5 feet or less 6 or more shots are needed.

D.     Avoid low f/values, (large apertures) below f/8 and short focal distances, it appears to be very difficult, if not impossible, to get well focused steps when the focal distances are small and the f/value is small. How do you separate 0 from 0 for depth of field???-you get my point!

 

With these recommendations in mind, the next section is a step through example using Focus Lite and a flat desk calendar as the object. This way one can easily follow the focused points used and contrast is optimum, black and white with pink mixed in.

 

Using Helicon Focus Lite

 

Camera and Calendar Setup:

 

1.    Five shots were taken with camera setup shown below.

2.    Point A is the number 27 on the calendar and point B is the number 6 barely legible in the first shot, Image C.

3.    Shots were taken with the lens focused on the numbers 20, 13 and 6 were focal points and mid-way between 13 and 6.

 

 

Text Box: Helicon Focus Lite Interface

  

 

I wonít go into all the details of how Focus Lite works but will explain the simple steps to get good results when using this very handy program.

 

 

Ok, letís see how we actually did. The span actually seen by the lens-sensor combination is not 8 inches from the number 27 to number 6, but 6.9 inches due to the 30 degree tilt of camera lens. Nonetheless we are talking almost 7 inches as a needed depth of field to get sharpness throughout. According to Nikkorís DOF tables for 105mm Micro-lens, the depth of field for our camera-object settings is approximately 0.75 inches and here, we are talking roughly seven (7) inches for the depth of field to cover the calendar span. Well, did we? One only has to look at Image E. I say Focus Lite did an admirable job, but the focusing wasnít too bad either! To really appreciate how well this Focus Lite does, just look at Image F. It is an enlarged area around the number 6 of Image E. You can actually see the separation of dots in the gray dotted-line - nothing is blurred out. This is credit to the lens and Focus Lite.

 

 

I highly recommend Helicon's Focus Lite if you want sharpness throughout your macro lens close-ups. You can purchase an annual license for $30 or a permanent license for $115 as stated in the Helicon web site as of 2009. Well, we now have the best of both worlds: close-ups that are sharp throughout or, if we so choose, ones that are only partially sharp - who could ask for more.

 

Kind regards,

 

Joseph. R. Votano

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