Wildlife Photography Tips 8 - Image Stacking
(I have received this request, so here goes. I will address some of the questions in this post, and follow up in future posts.)
OK, share a little more info with us if you will. Aperture, ISO, Lighting, Distance between photos, Overlap. Do you denoise and PP all of your photos before running thru your stacking program, or afterward. What flavor stacking software are you using. Using a macro slider or refocusing your camera, or are you tethered to a computer and it's making the slices for you. Fill us in and I'll think of another dozen questions.
Focus stacking and editing – How I shoot and edit.
I am new to the focus stacking process, but not macro work as I have a degree in Biological Photography and have been shooting close-up and macro natural history subject for the past 40 odd years. Hopefully you find some of this useful.
Lens choice, Aperture and Shutter Speed
I guess aperture and shutter speed will be the first on the list of items to ponder when setting up. I have always been into the “simplify, simplify, simplify” mode for a long time. I shoot with the 105mm Micro Nikkor lens because, uh, it is the only macro lens I own. Pretty simple. There are many focal lengths, reversal rings, etc., that could be used. Once you get something, just practice with it until you are very familiar with its qwerks and foibles.
I had the 55mm micro for more than a decade because I couldn’t afford the price of the 105mm. The 105mm, or any of the macro lenses near that focal length – 100, 90, etc., provide just the kind of working space, between front lens element and subject, to capture many critters who would be shy and difficult to get really close to. I shoot a wide variety of plant and animals and find the medium focal macros the best all-around.
When I have procured the specimen of choice (this will have to be on a different thread – Capturing and procuring the photographic specimen), I very rarely shoot wider open than f/11 and never stop down past f/16. In fact, I would say over 85% of the stacks, if not more, are at f/11. Shooting at f/16 provides me with more depth of Field (DOF), but I find the overall crispness in the final image requires more editing in post processing (PP). So it seems to save me some time with the stack blending process in the long run. Now most of the stacking I do is for images from 1.5:1 to 1:4. I have little desire while in the field, to attempt 2+ magnification shots.
For close-up and macro, I almost always shoot with an electronic flash…set to manual. Why? To simplify my exposures. Once I have determined the correct flash distance to provide f/11 properly lit, I have both the camera and flash set to manual, the lowest ISO my camera provides (100 with the D610 and 64 with the D810), 250/sec. Now my final concerns before capturing the images are number of slices (stacked shots) and timing for those exposures.
Number of Slices
For this post I will assume the subject is at 1:2 or ½ magnification. I will take a ruler or tape measure and measure the distance from the nearest part of the scene, to the farthest part in the scene that I want to be sharp. (NOT JUST THE SIZE OF THE SUBJECT). (By the way, any text that is in CAPS, is something I consider important).
Many times the habitat or scene context is important to the information I am supplying with the photo. It also provides me the control over the amount of DOF by allowing me to soften the foreground and background in PP as needed for final usage instead of having to reshoot the image. It is much like the reasoning for “not” shooting your images too tight. If a client requires text to be used with the image, your image won’t be used if someone else has provided space in their similar image. I call it “Play Space”. So be sure to have a bit of “play space” around your subject and the whole field is included in your calculations. You are dealing with 3 dimensions in stacking, so be alert to space in width, height, and depth.
After I measure from front to back, I will take on the average of 12 shots/inch of depth, increasing the number to 15-20/inch as I pass through the subject being shot. These numbers are not fixed because if I chose to increase magnification, I would also increase the number of shots. I have included an example of the method I use for stack shooting.
See Fig 1. In this figure, the scene does not have a lot of depth. The slices in red are a bit closer together than the blue slices. That is because the subject falls into the red zone – closer together means more data is collected for that area in which the subject is emphasized.
See Fig 2. In this figure, the scene has a lot more depth. The red slices are captures through the most significant part again, but you will also notice that the red slices are also closer together as you focus closer to the front lens. This area (orange shading) would be the same as if I were increasing the magnification by moving the lens closer to the subject A, (increasing its magnification). I would also shoot these captures closer together as the DOF decreases as I get closer. The area behind the subject still has the same spacing the blue lines have in Fig 1 as it is the same working distance as before.
Camera Placement and Capturing Method
There are different methods of image capturing. One is to hand-hold the camera and press the shutter release button at the precise moment you feel you are focused on the slice you want to take. If you have a steady hand, and you are not attempting too many slices with excessive magnification, this system could work for you.
The second is to mount your camera on a rail, which is in turn mounted to a tripod, then focus set for a specific focus magnification. The series of captures are taken as you move the camera up or down the rail. This usually provides a very sharp set of images due to the use of a tripod. The drawback to this method is that the sensor plane to subject is constantly changing and subsequently so is the magnification. Some of the software programs have worked out this issue and compensate for it during the post processing.
Another method I have used on occasion is having the camera tethered to the computer. This means you have software that runs the capturing process. They work well, but do not provide you with the ability to place some of the image slices closer than others, and you will be working with live view on your monitor instead of viewing the live image through the prism of your camera.
The method I have found most useful is having the camera mounted on a tripod, and focusing manually throughout the scene. This enables the camera sensor to shoot all of the exposers from the exact same angle at the exact same magnification like the tethering. But you have control over the distance between captures more quickly than tethering. This could be very important when shooting live specimens that move.
The next post will deal with the procuring and shooting the specimen.
Fig 3. This is an illustration of my basic tabletop setup. Flash with softbox, camera, and tripod. If it appears that the softbox is very close to the subject, IT IS. Placing the soft box so the light is diffused and as wide as possible, lessens the harsh shadows cast by the electronic flash.
I will deal with specimen prep and working with live animals in another post. I will also cover post processing on a later post as well. Stacking requires more patience than just shooting macro images. Be prepared to spend time in the setup and capturing process and you will do fine.