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 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.
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
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”.
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 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.
- 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