PlymouthWoodworker wrote:
I've tried 2 methods of focusing for macro focus stacking. The first is to keep the camera in a fixed position and turn the focus ring to focus at different depths by eye. The second is to use a rail on the tripod that allows the camera to be moved closer or farther from the subject without moving the focus ring. This method allows movement in measurable increments (matched to depth of field), but also changes the perspective slightly since camera-to-subject distance is changing. I would be interested in additional pros, cons, and preferences. Thanks.
I've tried 2 methods of focusing for macro focus s... (
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Linda mentioned my focus stacking so I'll share my opinions and experiences, both good and not so good. Essentially there are three ways to change the focal point, move the camera toward the subject with the focus point set, move the subject toward the camera with the focus point set and third is to keep both the camera and the subject locked in position (as much as possible) and change the focal point with the lens.
What may work best could depend on the lens used. Microscope objectives and reversed mounted lenses do not lend themselves well for adjusting the lens focal point. Many lenses used do not even have that ability. The goal is NOT to touch the camera. The slightest movements or vibrations are difficult to contend with and may result in blur and ghosting.
Helicon Focus Tube is a fantastic device for it changes the focal point of the lens and it is very, very good for focus stacking images in the field (it is great for studio work too). It would surely be my choice if I were to take to the field and it eliminates the guesswork of how far to manually turn the lens focus ring.
The distance of the "steps" are dependant on the camera sensor size (full frame, crop, etc.), amount of magnification and the f/stop. As magnification increases the distance of travel between shots decreases. When using microscope objectives at 10X, I am in the 8-micron per distance step for each shot in the stack and the number of images number in the hundreds.
Typical macro lenses do have some degree of depth of field although it may be very shallow. Flat dept of field lense have virtually no depth of field so each photo it takes is a tip of a hair thin. When venturing into that domain, computerized focus rails are a necessity and no vibrations can be tolerated. I have my camera rig mounted on a concrete floor on a 500-lbs laboratory cabinet with two inch thick granite and vibration isolators on the base of the cabinet and under the granite. I shoot in the mirror up mode and I pause 2-seconds between shots to let any transient vibrations settle. I operate the camera with the PC and after setting up the session, I never touch the camera and when I hit "start" I leave the room and all lights are out except for the subject's illumination. Of course it is not necessary to go to these extremes unless the goal is high levels of magnification which to me is between 10X to 20X.
Diffraction also increases as magnification increases so finding the sweet-spot of the aperture will vary from lens to lens. Reversing lenses and putting combinations of lenses in series plays into this as well. Extension tubes, helicoids, and bellows all affect the amount of light that travels through the lens and also impacts diffraction. Illumination and diffusion of light is both a joy, a pain in the butt, and a science in itself and it can make or break the resulting image.
Of course there is much, much more and if you would care to message me I would be happy to share as much as I can. If you'd like to see some of my work, here's my Flickr link
https://www.flickr.com/photos/153096150@N05/?