 Giordano |
Extension tubes or bellows? I'd like to try some macro photography, without buying an expensive macro (micro?) lens right now. What's better between extension tubes and macro bellows? Thanks
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Giordano |
P.S. I have a Nikon D70s with a 18-70 and a 75-300 lenses.
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Alan N. Marcus |
Hi Giordano, Many cameras lack the ability to close focus. As you focus closer and closer, the camera lens is caused to rack forward expanding lens to chip/film distance. As an example, a 35mm with a normal 50mm lens, when focused on distant objects, the lens to image plane distance is 50mm. When close focused to produce actual size (life size or 1:1 or unity) the lens to image plane is now 2 times the focal length. Stated another way, a 50mm lens focused at unity will be extended forward to the 100mm mark. The image brightness at the image plane is now 4x less bright than if focused on infinity. This is true because the magnified image would cover 4x more surface area if it were not cropped (not realized because it is cropped by the film or chip mask inside the camera). This 4x reduction in light energy requires 2 f/stops of compensation. This is known as bellows factor. Cameras with through-the-lens metering will react and compensate. Otherwise the burden is on the photographer. The standard lens is corrected for the infinity position. At close focusing positions the lens will always perform slightly substandard. The macro lens is corrected at the unity position and always performs slightly substandard at distance. However the macro automatically compensates for bellows factor. Standard lenses usually stop their forward movement when the bellows factor exceeds 1/3 of a stop. Use of tubes and bellows artificially allows the lens to image plane distance to be expanded. Generally tubes are easier to work with. They do not have the flexibility of the bellows which allows for an infinite range of lens to image plane distances. My advice is rings and tubes first then go up to bellows after you get your feet wet. Most standard lenses when mounted on bellows or tube will operate at improved performance if mounted backwards. Ring adapters allowing backwards lens mounting are available. Acquiring a macro is best. Least in quality but quite economical is the mounting of an accessory close-up lens sometimes incorrectly referenced as “filters”. These are actually simple magnifying lenses made just like ordinary reading eye glasses. When mounted in front of the camera lens, they permit close focusing. Best of all, no bellows compensation is required. They are rated in power using a system (unit of measure) known as the diaopter. 1 diaopter is 1000mm – 2 diaopter is 500mm – 3 diaopter 333mm – 4 diaopter is 250mm. You can go to the drug store and buy a couple of pairs of inexpensive reading glasses. These are labeled in the same unit. Try a # 3 by just holding them so one of the lenses is in front of the camera lens. After experimenting with reading glasses, if you like the result, buy one or two real supplemental close-up lenses. The better type is comprised of two lens element and is color corrected and coated. They won’t allow the super close focusing like the tubes or bellows but they can provide an introduction to the exciting world of close-up photography. Alan Marcus
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doug Nelson |
One way to do quality macro on the cheap is to buy any name brand manual focus SLR used, and its brand mate 50mm macro lens (or a 90 to 100, if you like having some space between camera and subject). A good candidate would be a Canon FTb and 50 or 10mm Canon manual focus macro lens. You might get the whole set-up for less than $150. The old FD 50mm f3.5 macro is superb.
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Giordano |
Thanks a lot for your help Alan and Doug. I've seen that most of the extension tubes do not have any electronic connection. Can I use them with my G type lens, focusing manually and at max aperture, playing with the time? Or I have to buy a manual lens to work with them? Thanks again Giordano
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doug Nelson |
Extension tubes with electronic connections cost as much as the whole outfit I described. Depth-of-field is the important element to control in macro. At wide apertures, it's paper thin. You will want a bright screen with which to focus very precisely, and a way to let the aperture call the shot, while the camera compensates with a shutter speed. Want a truly ideal set-up for this? The old (1st or 2nd) version Canon F-1 meters a 12% rectangle, a semi spot. The camera may come with, or you can buy on auctions, an extra bright Laser Matte focusing screen. Canon macro lenses, extension tubes and bellows are dirt cheap these days. Lay out a little more for the 3rd version F-1 with standard bright laser screen and eliminate the battery hassle of the old F-1's. All F-1's take the Speed Finder (the 3rd version has its own), which gives a huge viewfinder picture, making focus even easier. It is nice to have, but certainly not essential.
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