Tripods are a great help in stabilizing a camera while shooting. However, like all things in the real world, tripods are not perfectly rigid. They can vibrate, and they can sag under the load of camera equipment. Some of their drawbacks are dictated by compromises in weight and cost - it is entirely possible to build a tripod that resists all vibration and sagging even on a microscopic scale, but it would weight more than a photographer can lift, and would require a reinforced concrete foundation to operate.
Even among real-world tripods designed to be used in the field, the most solid models, like the Gitzo Series 5, are too heavy to be carried significant distances in the field, and eat up a significant portion of the checked-in luggage allowance when placed in a suitcase to be carried on a flight. For this reason, my Gitzo G1548 is my favorite tripod for indoors use, but does not see any travel.
One of the worst enemies of a stable tripod is often built into the tripod itself. Many tripods have a central column that slides out from the top of the tripod, extending its length. The column is so handy, especially on a tripod insufficiently high to bring the camera to the photographer's eye level, that one can hardly resist the temptation to extend it. This causes the central column to flex and vibrate, and should be avoided. Even when the column is not extended, its topmost portion and associated collar and mechanisms still introduce some flexing and vibration.
There are situations where a special type of central column is indispensable, e.g. to move the camera away from the center of the tripod for macro shooting. For general photography, however, a central column is simply not useful. In this case, then, why build a tripod with a central column that the photographer cannot avoid to carry around at all times?
Another problem with central columns is that they do not allow shooting from ground level. Most tripods allow their legs to make a leg split (or spread-eagle), i.e., to be folded radially away from the central hub. The central column, however, remains in the way and the spread-eagled tripod cannot be used to place the camera near ground level (the column can be fully raised, but this defeats the purpose of the spread-eagled legs).
Gitzo places its Series 2 and 3 tripods in the category of (relatively speaking) small and lightweight tripods for professional use. The series 2 is especially lightweight among professional tripods (not among cheap amateur tripods, which we are not considering in this discussion) and attractive for traveling. This brand and series are very popular among nature photographers. Gitzo has carefully listened to its customers, and currently produces the Series 2 and 3 in Systematic models featuring a big round hole at the center of the tripod hub. In the past, only the Series 5 had a similar (but larger) hole.
The hole can be plugged with a flat magnesium-alloy plate or a tilt adjustment base, which completely replace the column, or with different types of columns for those who cannot live without them. But what about the older Series 2 and 3 models with no way to replace the column with a platform? Should their owners simply throw away these tripods and buy new ones? This would make Gitzo happy, but these tripods are not cheap, and are designed to outlast an ordinary photographer.
For owners of the many Series 2 and 3 Gitzo tripods with built-in central columns (Gitzo still makes and sells them to photographers who haven't yet wisened up), Markins comes to the rescue. This brand is well-known for professional-level tripod heads and accessories, and for several years has been quietly selling special tripod platforms that can turn a Gitzo Series 2 or 3 tripod with an "obligatory" central column into one without a column. Some of these custom platforms only require the photographer to remove the central column and a few accompanying parts, which can be done without tools. The columns can quickly be put back if desired.
Other types of Markins platforms completely replace the central hub of the tripod, and require the legs to be disassembled from the original hub and reassembled on the new one. This is meant as a permanent modification, although in principle it is reversible. It saves some weight with respect to the simpler modification, and can reduce the height of the platform above ground (but not by much). The permanent modification is also significantly more expensive. Different Markins models are used for the Series 2 and Series 3.
Some Gitzo models may be incompatible with these Markins products, or may require additional parts. Make sure you collect enough information before ordering anything.
For my old Gitzo G1227, I chose the simpler modification, the Markins TB-20. The accompanying instructions, like the assembly process itself, are very simple. Just remove the central column and all the accompanying parts that easily unscrew or slide off, and screw on the cup-shaped TB-20. Some of the smaller accompanying parts are not used with all Series 2 tripods (in my case, a black ring with a threaded hole in its center), and some of the original Gitzo parts can be reused on the Markins modification (in my case, the bolt that carries a hanging hook at the bottom of the column).
The 3/16" threaded bolt screws into the middle of the platform, and a threaded tube attaches to it at the bottom and fixes it in place. The length of the bolt projecting above the platform is adjustable before the threaded tube is tightened. Don't make it too short or too long for the tripod head. The Gitzo hanging hook can be screwed into the bottom of the tube, and can be removed for shooting from ground level.
The TB-20 is available in black, blue or red. I prefer black to avoid the risk of bright colors reflecting on subjects with mirror surfaces. It is simpler to avoid these reflections by using black equipment, than by dressing up the tripod with a burka.
The result is a much steadier tripod than the original G1227 with column. Even with the column fully lowered, the original tripod suffered from vibration, but is now detectably steadier. I also had trouble keeping the column locked, since it always seemed to find a way to rotate or slide within its chuck, no matter how hard I turned the retaining ring.
This modification does not magically eliminate all sources of vibration and sagging (the rubber feet, floor and photographer's movements around the tripod remain, for instance), but it does eliminate one major source.
The tripod can now be used to shoot from almost ground level, for the first time in its lifetime. With spread-eagled legs, the tripod platform is 73 mm above the ground, mostly due to the Gitzo column sleeve built into the tripod hub projecting slightly below the leg articulation point. A solid ballhead like the Sunwayfoto XB-52 brings a camera to the right height for use of the viewfinder while laying down on the ground. A bean-bag under the center of the tripod can slightly increase its height for better comfort.
A Markins-sponsored report on the vibration properties of the G 1227 with original column versus TB-20 is available at http://markins.com/charlie/report4e6.pdf. It makes for some dense reading, but as far as I can see, this report supports my qualitative findings about the TB-20 reducing the amount of tripod vibration, with respect to the original column. As mentioned above, this is an important advantage, but not the only reason for switching the column with a TB-20.
. The Markins TB-20 replaces the central column of Gitzo series 2 tripods equipped with a built-in column. This removes a major source of tripod sagging and vibration, and allows shooting with this tripod from almost ground level. For owners of Gitzo Series 2 and 3 tripods with "obligatory" columns, this and similar types of Markins platforms are the easiest and cheapest way to make their tripods steadier and more versatile.