Photography: Appreciation through Understanding

The vanishing DoF at large magnifications – CombineZM to the rescue

Comments[0] 05:14PM Jul 15, 2007 by Charles in General

When the magnification is greater than 1X, the depth-of-field (DoF) becomes paper thin; and 3D objects cannot be imaged very well.  For subjects that are completely still, one can take a series of photos with different focus setting and then attempt to combine them.  By this I mean the construction of a composite image by using the sharp parts of the component images.  If you have tried this, you know that there are problems.  First of all, our camera lenses are not telecentric, and the magnification changes with the focus setting.  Therefore, the first step is to resize the images before trying to bring them into register.  With more than a couple of images, this gets to be a lot of work.

As you probably know, there are computer programs for image reconstruction and DoF expansion.  One review of such programs can be found at:  http://www.crystalcanyons.net/pages/TechNotes/3DMicroMacro.shtm

Here Prof. Hart compares various programs and concludes that the freeware program CombineZX does rather well.  Information about Combine ZM can be found at:

http://www.hadleyweb.pwp.blueyonder.co.uk/CZM/Manual/combinezm_help.htm

 
A couple of weeks ago I downloaded CombineZN and finally got around to testing it.  I have only used the automatic mode, but I am impressed.  Here I show a few images to serve as an illustration.  The shots were taken with a Sigma 150mm lens at close to 1:1 focus (1X magnification) with 68mm of extension tubes added to bring the magnification to 1.68.  In all cases I used f/5.6.  I took seven shots with a change in focus the same direction each time.  These are photos of a fly about 2mm in length that has been trapped by a Cape Sundew plant.  In the first image (148 kb, jpg)  I attempted to focus on the closer eye, and the problem with DoF is obvious.  The second image (209 kb, jpg) was constructed by CombineZM from a stack of seven jpg images.  This image was satisfactory from the start, but I did improve a few places with the clone tool.  I have a lot more to learn about CombineZX, but I thought that you might enjoy playing with it also.

By the way, the plant is small.  This photo (228 kb, jpg) puts it all into context.   

Diffraction Problems in Macro Photography

Comments[0] 04:11PM Jul 15, 2007 by Charles in General

Avoiding diffraction problems in macro-photography:  We all know about the loss of resolution that occurs with small apertures (large f#’s), but it is easy to forget that the effective f# is not equal to the one shown in the camera.  The f# we need to use is: f#(effective) = f# times (1 + m).  Here m is the magnification.  My Sigma 150mm macro lens will focus to 1X magnification.  At that point all the f#’s shown should be multiplified by two in order to estimate the DoF and the effect of diffraction.  It gets worse with extension tubes.  I add 68mm of additional extension to get 1.68X and the f#  shown needs to be multiplied by 2.68!  When I forgot this factor and set the camera for f# = 22, I got unsatisfactory images.  As an example take a look at this figure:

Sundew plant (100% crop of 1X macro photos) (635 kb, jpg)

The setting of f/4.5 is probably the best and f/8 is satisfactory, but f/22 is fuzzy.  You can find useful information in John Shaw's book, "Closeups in Nature."

All chapters temporarily off-line

Comments[0] 09:20AM Jun 02, 2007 by Charles in General

Chapters 1 - 9 have been taken off-line while revisions and consolidations are being made.  The tentative table of content of contents can be seen here.

Chapter 9 at last

Comments[0] 06:41PM May 07, 2007 by Charles in Lenses

I am now posting Chapter 9: 
Coming to terms with real (compound) camera lenses  (pdf, 230 kb)

This chapter contains math, but I think the basic ideas can be appreciated without working through the derivations.  Of course, some of us love math, and that is why it is here.  An equation is certainly worth a thousand words!  As always, comments will be appreciated.  Also, please continue to report suspected errors via comments or in email.  Thanks.

Birding in Costa Rica

Comments[0] 06:16PM May 07, 2007 by Charles in General

Exploring Costa Rica with a camera was a great adventure.  We spend spend two nights each at five life zones.[Read More]

Birding trip to Costa Rica

Comments[3] 10:55PM Apr 06, 2007 by Charles in General

I will be on a photo shoot in Costa Rica for the next two weeks.   "Science in Photography" will be on hold, but I will be having fun trying out a Canon 70-300mm IS lens, a Manfrotto 676B monopod, and a Better Beamer.

Updated Table of Contents

Comments[0] 03:11PM Mar 31, 2007 by Charles in General

I have completed Chapter 9 on understanding compound lenses, and I am now getting help with proof reading.  Also, I have updated the Table of Contents.  The new version is available here.

Figures for Chapter 4

Comments[0] 08:43PM Mar 15, 2007 by Charles in General

New figures have been added to Chapter 4 (pdf, 188KB) to illustrate changes in image size and perspective, and work is proceeding on Chapter 9: 

 Tentative Title for Chapt. 9:

 Coming to terms with real (compound) camera lenses

(Nodal planes, entrance pupil, stops, and all that)

I expect to be able to post Chapter 9 in a couple of weeks.

Lens Equivalents

Comments[0] 12:18PM Mar 04, 2007 by Charles in General

I was happy that Nathan Myhrvold noticed my essay “Lens Equivalents,” on Luminous-Landscapes and that he took time to comment on it.  Our discussion/debate was a lot of fun, but a face to face discussion would have been much better.  Debates online never seen to be completely satisfactory.  Probably because feedback is delayed, and one cannot see immediately which points are being accepted and which are not.  Also, I suspect participants do not read carefully enough comments that appear to contradict their own.

Chapter 15 (tentative)

Comments[0] 06:23PM Mar 02, 2007 by Charles in Vision

Here is a draft of Chapter 15:

The Limits of Human Vision – How Good Does a Photographic Image Need to Be?

 (pdf, 214 KB)

Biology is not my forte, but I do like to learn things.  I find the design and operation of the human eye to be fascinating and certainly relevant to the design of photographic equipment.  I am on thin ice here, so please help me with your suggestions and criticisms.  If you prefer to contact me by email, check the “About page” in the upper left hand corner.

Chapter 8

Comments[2] 12:34PM Feb 26, 2007 by Charles in Lenses

This post offers a draft of Chapter 8:

Chapter 8:  How to Make Lenses That Are Good Enough for Photography

(pdf, 276 KB)

This one concerns the complexity of modern lenses required to correct aberrations, minimize flare, etc.  It is fairly brief, but it covers a lot of ground.  As always, comments are appreciated.  I would certainly like to correct errors and misconceptions; but I also need to find out what parts are not understandable as written.

Chapter 7

Comments[0] 11:24AM Feb 19, 2007 by Charles in General

With this post I am presenting:

Chapter 7:  What is behind the rules of optics?
(pdf, 98KB) 

This chapter deals with modern physics and the rules of optics, and it provides a glimpse of the strange universe we live in.  It is far removed from practical photography, but it does introduce ideas that are useful in understanding optics in general and, in particular, the interference effects we will encounter with lens coatings.  If this kind of thing does not interest you, feel free to skip ahead to lens design issues, etc.

 The updated, but still tentative, Table of Contents can be found here.

Chapters 4, 5, and 6

Comments[4] 10:25AM Feb 17, 2007 by Charles in General

Chapters 4, 5, and 6 are posted.  Comments, are appreciated.
[Read More]

Pixel size, F-stop, and resolution

Comments[7] 02:20PM Feb 15, 2007 by Charles in General

Resolution tests are presented for different pixel sizes at a variety of F-stops.[Read More]

Chapters 1, 2 and 3

Comments[3] 03:50PM Feb 13, 2007 by Charles in General

With this post I am making available the following Chapters:

1.  What is photography

2.  What is Light

3.  The Camera

I would appreciate any comments.  Additional chapters will follow in a few weeks.