Azure A's List: Photography

• Reversing rings are also made that have male filter threads on both sides. These rings are used to make "lens combos" or "stacked lenses" (distinct from focus stacking), by reversing a short lens in front of a long lens. In that case, the overall magnification is simply the ratio of focal lengths, rear/front, so for example reversing a 50 in front of a 200 will give you 4X magnification. Stacked lenses are commonly used with compact cameras that do not have interchangeable lenses. They are also used sometimes on DSLR's, particularly to get high magnification in the field. In my experience, most lens combos don't actually give very good images, due to aberrations that appear because the lenses were designed to be used separately, not together.

• If you’re curious if your setup is capturing a 1:1 or better ratio, a super simple way to test it is to take a photograph of a ruler using the setup you want to measure. Look up the size of the sensor in your camera (A Nikon D90, for example, has a sensor that is 23.6mm wide) and compare that size to the what the camera captured. If you’re capturing at least 1:1 then the portion of the ruler visible in the photo will be 23.6 mm or less (if you could only see roughly 11.8 mm on the ruler, for example, your setup would be reproducing the subject at a 2:1 ratio). Conversely if you can see more than 23.6 mm on the ruler than your setup is producing photos that could be considered close up photos, but not true macro photos.

• wide-angle lenses take a large landscape area and focus that on a small area in the camera, reversing them hones in on a small subject area, and spreads that over a larger area on the sensor.
• Reversing any lens shorter than a 60 mm focal length turns it into a macro lens. In order to make aperture and focus adjustments while the lens is reversed, it’s best to choose a lens that has both a manual focus adjustment as well as an aperture ring. While it’s possible to hold the aperture pin to stop down the aperture with newer automatic lenses, at this magnification the slightest camera or subject motion shows up in the final photo.
• I thought I’d also take a look through my 105 mm macro lens backwards to see what a longer focal length would do, and it simply doesn’t produce a useable image. One issue to remember with a reversed lens is the inside element is exposed when photographing, so be extra careful!
• camera mounted on a tripod that features an articulating center column. That makes it easier to set the camera up, adjusting it so the subject’s plane of focus is parallel to the camera’s sensor.
• An important factor to remember for composition is that as the magnification increases, the depth of field decreases. With the 24 mm lens at f 22, the depth of field is only about the thickness of a dime.
• there is no data connection between the camera and lens with the lens reversed, so the exposure must be done with the camera in Manual exposure mode. The aperture is adjusted on the lens, and the shutter speed and ISO are adjusted on the camera to achieve a balanced exposure.
• unless the exposure is at least 1/125 second or shorter, the vibration from the mirror swinging up causes blur from camera motion. Work with the mirror lock-up feature or exposure delay mode (Nikon) to be sure the camera is completely still during the exposure.

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