Expanded depth of focus: Trouble Shooting

sml purp pr c grn (c)“Let the beauty we love become the good we do.”  -Rumi

This is the second in a series of blogs about the photographic technique called expanded depth of focus. For this, multiple digital photos are  taken of the same subject, all identical expect for the area of sharp focus. Then, by computer processing,all the different areas of crisp focus are combined into a single image which is entirely in focus. This allows images to appear more life-like. It is one of the marvals of digital photography that cannot be duplicated with film images.

If you are unfamiliar with this photographic technique, but somewhat interested, please check out my blog post from July 16, which is an introduction to the topic. If you are knowledgeable about this topic, but have no interest in trouble shooting yet, please go to my next post entitled “Philosophy”.

Now I will address the individual who has tried this photographic technique  unsuccessfully. I am referring to those who are saying, “I did everything right, so what went wrong?”  

Being aware: Fully 95% of my unusable series are due to an error of mine that I did not recognize at the time. I overlooked a problem that, if recognized, could have been corrected at the time it occurred. I know this, because as I get more experience and become more aware, I get a much greater percentage of excellent results.

I will be assuming that you used the proper equipment and technique as briefly noted in my post of July 19 (Table of Contents). Some, not all, of my assumptions are that you:

  • used a camera with enough megapixels and file size and file format to give sharp focus for the amount of enlargement required for your computer screen and your planned print size.
  • utilized a lossless file format. Raw images are best.
  • used a focusing rail
  • used mirror lock-up mode for DSLR’s
  • used a shutter release cord or remote control if mirror lock-up is needed
  • used small enough increments between focal planes that the areas of sharp focus overlap. This is critically important, because areas of focus must overlap. Thus the increment of advancement of the focusing rail between frames would be, at most, 1/3 of the lens’s depth for that distance from the subject. Specificly, if a  macro lens is 10 inches from the subject, the depth of sharp focus may be only 3 millimeters (about 1/8 inch) deep. Therefore the increment of advancement of the focusing rail will need to be no greater than 1 millimeter (1/24 inch). However when 3 feet from the subject, this same lens may exhibit a depth of field of 48 mm (2 inches). In this case the correct increment would be, at most, 16mm (0.7 in). To determine your lens’s characterist, take an image of a ruler end on. Take images at the lens’s closest focal distance, then double the distance and double it again. The measurements do not need to be precise. On your computer, evaluate how many sixteenths of an inch are in crisp focus. one third of that distance is the largerst increment between frames that will give good results.
  • been meticulous to avoid any movement of the subject by air movement or change in the shape of the flower due to heat change.
  • used editing software that allowed you to compare and confirm focus and location precisely among frames
  • used sophisticated software for generating your composite
  • were knowledgeable and adept in the use of your software

  Trouble shooting is an expansive topic. Here I will cover only some of the more sneaky problems.

 Tripod

  • Tripod feet can settle into soft ground or leaves, changing the camera position.
  • If tripod was bumped, it may not have returned exactly to its original position.
  • If all of the tripod leg locks/collars was not fully tightened. A leg can shorten, changing the camera position.
  • If the tripod legs were not splayed all the way to their stop, they can spread causing a change in camera position. This is most often a problem when shooting from a low enough angle that the legs needed to be spread wider than usual.If your camera position is low enough to the ground, the center post can touch the ground, allowing the tripod to  rock.

 Camera

If the camera is not fully tightened to the focusing rail, it can slightly twist/torque. This is most likely when shooting in a vertical orientation. That happened to me this morning. I noticed & corrected before any harm had occurred.

Tripod head and focusing rail.

Similarly, if either of these is not firmly secured, they can twist/torque, shifting the position of the camera

Aperture

If the aperture was more than 1 stop away from f/8, the sharpness will be less than the camera /lens is capable of producing. For most lenses, f/8 usually provides the best combination of sharpness & depth of focus. I know that landscape depth of field is considered best at f/16 or a smaller diameter. This does not apply here. I will go into detail about this in 2-3 more blogs from now entitled “Aperture”.

Exposure problems

1) Viewfinder of a DSLR camera, if not covered/capped, will let in light that changes the exposure. This is particularly a problem when direct sunlight falls on the viewfinder.

2) Focusing rail, if not locked with fine/precise lock at each incremental focal distance will change subject location too much. Additionally, if focusing rail was not firmly tightened onto the tripod head, it can twist causing movement of the subject

3)Soft, unsharp images

  • File size too small. In the shooting menu, set file size to the biggest numbers that is offered.
  • Too little data or date loss. This is a problem with jpg images. Shooting in RAW format is recommended for many reasons.
  • Stray light: There may have been bright light impinging upon the lens at a sharp angle.  A lens hood prevents most of this. Check with the company that made your lens for the specific one to use. Some cannot be used for macro work because they cast a shadow upon your subject. A polarizing filter is highly recommended when shooting outdoors and when shooting shiny, wet or alive objects indoors. Besides enhancing colors and decreasing reflections, it usually blocks stray light and can take the place of a lens hood. However, I shoot outdoors with reflectors producing very bright light impinging upon the surface of the polarizing filter from multiple directions. For these conditions, I think that a lens hood and a polarizing filter give the best results. Besides enhancing colors and decreasing reflections, it often can take the place of a lens hood. However, I shoot outdoors with reflectors producing  bright light coming from many directions. I find that a lens hood and a polarizing filter seem to give the best results.

 Lens

  •  Lens distortion is particularly a problem when your subject enlarged or “bloomed” out near the edge of the frame.  That presents bizarre data from this area to your stacking software. However, the central portion of the frames will probably give good results. Some editing software can remove lens distortion. I have experience only with Canon’s Digital Photo Professional software. It will remove the distortion of some Canon lenses, but it’s time consuming and this does not guarantee that it will give good stacking results.
  • Focusing ring/collar was touched when reaching for the camera or focusing rail. This can happen even when there’s no noticeable movement of the focusing collar. I have to be careful about this because I steady the camera with my left hand while changing the position of the focusing rail with my right hand.

Subject moved

  • Change of support structure: If a flower is getting even the slightest support from one of its petals or leaves (or a petal, leaf or stem of an adjacent flower) any subtle change of its shape can allow a shift in your subject’s position.  This is more likely if there is an intermittent breeze or if I potted plant has recently been moved.
  • Similarly, if a petal, leaf or stem of your subject flower is in contact with petal, leaf or stem of an adjacent flower, then any movement from a breeze can move your subject flower. If there are lots of leaves touching, movement of any portion of the plant can move your subject. To prevent this, wait until there is no movement of any part of the entire plant before shooting. The more complex the interactions among the plant parts and the stronger the wind, the more likely it is that your subject will not return fully to its original position. Although this is true, I shoot outdoors all the time and find this problem to be rare unless the intermittent wind is quite strong.
  • Flowers frequently change shape during a shoot if they were freshly cut or if they were recently moved from shade to direct sun or vice versa. I find this less of a problem if a cut flower has only the bottom ½ inch of the stem in the water.

Because there are so many possible problems, I recommend shooting two series of everything when beginning to get experience with this technique. Start the set up for the second series of images from the very beginning, just as though it was the first series.

I hope this has been useful information for someone. You are welcome to ask me about particular issues that you would like help with.

If anyone would like assistance with processing of their photos, please check out my web site at NaturePhotoRehab.com

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3 comments on “Expanded depth of focus: Trouble Shooting

  1. LubbyGirl says:

    This is very informative – thank you for sharing your knowledge. I’m such a beginner at photography, but I love it so much. Many of the things you mentioned here (like mirror lock-up mode and focusing rail) I don’t know, but now I will have to find out! I have a Sony DSLR and am trying different things with it, to learn how it works.

    • Thank you for your kind words.
      Welcome to a world of magic and “miracles”.

      Sony makes great DSLR’s. Your approach of taking your time and trying different things with your camera is perfect.

      I have given some more information about mirror lock-up in my blog from last night (Sharper Photographic Images – Part 2). Its importance is that in DSLR’s an internal mirror pops up and away from the sensor immediately before the shutter opens (“mirror slap”). This mirror motion causes a slight and very brief internal camera shake during the time when the shutter is open. In mirror lock-up mode, the first press of the shutter release button causes the mirror to go up and stay up (and the viewfinder and screen goes dark). Press the shutter release a second time and the shutter itself is activated and the viewfinder and screen return to their normal function. Mirror lock-up is used in conjunction with a corded (plug into the camera) shutter release button or a remote control. Your camera may have come with a remote (wireless) shutter release. If so, it will work fine. Mirror lock-up improves the sharpness of images from tripod work, particularly close-ups. It’s not useful, however, when a camera is hand-held. Mostly mirror lock-up is used by photographers wanting to achieve absolute sharpness for enlargements and framing or for having a more sale-able images. I use it whenever my camera is on a tripod.

      A focusing rail attaches to the tripod head. Then the camera is mounted on the focusing rail. This rail is useful only for very close-up work such as flowers. When the lens is close to the flower, the usual focusing ring/collar on the lens makes too big an adjustment to be useful. The focusing rail allows tiny and back-and-forth movements of the camera to fine tune the focus. They are expensive. A focusing rail is not likely to be worthwhile for you at this time.

      Thank you again for your comments.
      I hope to hear from you again, not only regarding my blog topics, but about any photography questions that you may have.

      • LubbyGirl says:

        Wow – thank you for this reply. I learned a couple of things I had no idea about. Now I know why I’ve never heard of these two things, cuz I don’t have them. But I still thoroughly enjoy my camera, and some day, Lord willing, I’ll be able to afford one of those focusing rails – AND a super-duper zoom lens that I’ve been drooling over. As close as I’ll come to owning one is if the store is disgusted with the drool all over it and gives it to me. 🙂

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