What are the potential focusing problems involved with macro photography? Please explain what you mean fullyThe technical definition of macro photography is that you must be shooting lifesize or greater. In other words, your subject must occupy the same size on the sensor as it does in real life. Focusing at 1:1 is relatively easy, but as you increase magnification into more extreme macro (ie 1:1 to 10:1), focusing becomes very tricky. when you shoot extreme macro, the distance to subject is tiny and the focus plane even smaller Us humans are able to focus cameras because the actual object in focus is buffered by some additional depth of field. But, both the plane in focus and the depth of field area are a percentage of the distance to the subject, and when you shoot extreme macro, the distance to subject is tiny and the focus plane even smaller. It can be less than 1/10mm in the case of extreme macro, and on a subject 3mm long it means that only the tiniest sliver of the object is in focus. Even shots at narrowest aperture, ie with the widest depth of field, still suffer from this same depth of field limitation, which is dictated by the laws of physics!
What are your favourite ways of solving these problems? Please discuss the techniques that you use as well as any other options that are available to photographers when photographing macro subjects (e.g. flash, tripods, narrow apertures etc etc).Various accessories are available to help photographers focus when doing extreme macro. In the field, doing single shot extreme macro, rather than focusing through the camera and adjusting the lens focus ring to focus, it is more efficient to keep your camera at a fixed focus point and move the camera back and forth until your image is in focus. A further option, if the subject stays still, would be to take a sequence of such shots and focus stack them. Stages range from the relatively cheap (£10, ebay) to high precision, electronically controlled (£500, stackshot) If you have more time on a relatively still subject, you can set yourself up with a camera on a tripod and a ‘stage’. A stage is a device that lets you move your camera back and forth, and following the same principles as above, the photographer can move the camera in and out a focus plane to take a sequence. Stages range from the relatively cheap (£10, ebay) to the best of breed, high precision, electronically controlled (£500, Stackshot Stacker).
What is focus stacking and how do you use it in your photography?Focus stacking is a process that overcomes the depth of field limitation with extreme magnification macro photography by bringing the focus planes of many images into one master. This creates an image that is factually impossible to create in a single shot, because of the depth of field limitation dictated by the laws of physics. Focus stacking has the most obvious application in extreme macro but every optic has a limit to its depth of field Focus stacking has the most obvious application in extreme macro but every optic has a limit to its depth of field. Even the camera on the Mars Rover has focus stacking built inside, to send those nice sharp Mars landscape pictures across the gulf of space. More about focus stacking at http://extreme-macro.co.uk/focus-stacking/.
What are the challenges involved in focus stacking and how do you overcome them?To focus stack successfully, the photographer has to overcome a number of challenges: mechanical, optical and visual. Mechanically, the photographer has to ensure that the images are shot in a straight line so maintain their alignment, that the increment between successive shots is correct to overlap nicely when stacked, and that the shots are all individually sharp enough to combine into a sharper overall stack. The latter can be a particular problem if continuous illumination is used. because even the tiniest vibration can cause blurryness on a 2 second 10:1 extreme macro shot. Optically, regular lenses don't have the resolution that we'd like Optically, regular lenses don’t have the resolution that we’d like which is why we tend to use specialist industry lenses, microscope objectives or inverse enlarger lenses designed for flatfield performance. The latter is a great value for money way to get started, and there are some good examples of lenses that don’t break the bank at http://extreme-macro.co.uk/reversed-enlarger-lenses/.
Visually, focus stacking benefits from nicely diffused lighting, and photographers go to great lengths to get their lighting right for their focus stacked image. This is quite the fine art and moving a light source by even a few millimetres can have a profound effect on the dynamic scale that the eventual image has.
What is your workflow for focus stacking, from capture to processing? What steps are involved?Focus stacking is not a quick process, and a number of steps need to be completed in turn to make the final result sing. Preparation of your subject before the image takes a long time, and in the case of insect specimens, requires specialist entomological skills and techniques such as relaxing, carding and pinning Preparation of your subject before the image takes a long time, and in the case of insect specimens, requires specialist entomological skills and techniques such as relaxing, carding and pinning. These are typically done using custom-made tools, under a stereo microscope, and can be the hardest part of the process for the non-entomologist. Photographic preparation includes making sure that the subject is in focus, testing the background, testing both ends of the complete run and testing the lighting. Everything needs to be ready to go before the final focus stack run, and of course you have to check common sense things such as making doubly sure that you have batteries with enough charge to complete the whole run.
The run itself is a mechanical excercise, and of course caution needs to be taken that each image is shot as carefully as possible, and that everything is consistent between images. This can mean reruns because of subject vibration or inconsistent frames when the lighting is not consistent, as can happen with flash units that are popping off several hundred flash pops for a run. I usually have the lights off and a positioning light focused on the subject during the course of the run.
The images are then transferred over to your PC/mac, and the stack itself is then created using stacking software such as Zerene Stacker. Depending on the complexity of your subject you may need to start with substacks and combine these into a final stack. Because of the permutations possible with Zerene Stacker, I preprogramme the permutations and usually ask my PC to do these overnight for me. A deep stack can combine hundreds of images and it takes computers some time to work through and stack all these, hence the overnight run.
Lastly, postprocessing. My main tool for bringing out as much detail as possible is Topaz Detail, and this does a very fine job indeed, used cautiously. Like any image there may need to be alterations in levels in photoshop, and as a last step, noise removal.