Manfrotto 501, Gitzo G1321
The Manfrotto 501 is a viscous-dampened tripod head for medium-weight videocameras. It is relatively cheap, and not extremely large and heavy. It mounts on a tripod with a standard 3/8 in. screw, and has a built-in quick-release shoe for a video plate (about 51 mm wide, available in two or three different lengths, starting with 90 mm). A 90 mm plate is supplied. A camera or long lens can be mounted on a plate with one or more 1/4 or 3/8 in. screws. One or two of each are supplied with the head and each separately purchased platform. One screw of each size can be stored in tapped holes under the shoe.
Like all video heads, it only allows tilting forward and back plus rotation around the base of the head. Other, larger video heads have a built-in levelling half-sphere at their bottom, which sits in a cup-shaped depression built into the top of a video tripod. The 501 head, instead, has an ordinary tripod attachment, and therefore does not require a video tripod.
The base of the tripod on which the 501 head attaches must be levelled to be horizontal, or the head will tilt sideways when panning. In the field, it is impractical to level a tripod accurately by solely adjusting the length of its legs. Therefore, I use the 501 head with a Gitzo G1321 levelling base that mounts on a G1548 tripod (above, with padded leg wraps from Wildlife Watching Supplies).
The G1321 levelling base has a top flat platform mounted on a metal hemisphere, which sits in a cup. Tilting of the hemisphere within the cup performs the levelling. The bottom of the cup has rims of two different diameters to fit into the top "holes" of Gitzo Series 3 and Series 5 tripods (where, as an alternative, you can mount a flat platform with a central screw, or a column). The rubber-coated handle that extends from the bottom of the cup is used to help with levelling, and is turned to lock the hemisphere against the cup. A bubble level is available on the G1321 (another one is placed near the bottom of the 501, but the Gitzo one is more precise). The lever visible on the side of the G1321 in the above picture is used to tighten the screw that attaches the head to the platform. This makes it easy to attach a head tightly, as well as to detach it.
The 501 has a small lever to lock the platform, and a red plastic safety catch to release it completely. The friction control for the vertical tilt is located on one side, and a locking knob on the opposite side. The locking knob must be tightened hard, and increases friction gradually rather than blocking the tilting completely (in practice, it works much like a second friction control). The head will not creep when locked, unless the load is strongly unbalanced. It can be balanced while inclined at different angles by shifting the plate forward or back within the shoe - long plates are best for this (unlike larger Manfrotto models, the 501 head has no tension springs for balancing a load). A friction control for the pan movement is located below the camera platform (it can be operated from the front or back, or exposed by tilting the camera shoe out of the way). A small locking knob for the pan movement is located on the base of the head, and locks this movement quite tightly.
The handle can be attached on the right or left side (the latter makes more sense with a DSLR), and its inclination can be amply adjusted.
The camera plates for the 501 are not compatible with the similarly shaped ones used in the Manfrotto/Bogen 3273 quick-release shoes (the latter are much wider). It might or might not be compatible with the plates of the 577, RC3 and RC5 quick-release shoes (I don't seem to find size specifications for these, but I do know that there are two different widths).
I use the Manfrotto 501 principally for shooting wildlife with telephoto lenses of 300 mm or more, often from a hide. The relatively heavy head assembly and its dampened movements provide a stable base, although I try not to use exposure times lower than 1/250 for 300 mm lenses or 1/500 for longer ones. I do not lock the head, and follow the movements of the subject in the viewfinder by holding the handle of the head with my left hand. I trip the shutter with the right hand placed normally on the camera, and move the right hand to the zoom and focus rings if necessary. It is not practical to do so with the left hand, because tilting or panning without using the handle requires too much force, and the left hand is better left on the handle at all times.
Compared with the older Manfrotto 136 video head, the 501 is significantly larger and more rigid, because of the design with the tilt axis held at two positions located several cm from each other. The 501 is not much heavier, because it uses plastic in a few non-critical parts (especially the cover for the tilt and pan mechanisms). Also unlike the 136, the 501 has no safety to limit the amount of tilt.
There are alternatives to the G1321 levelling base, but none that couples directly with the series 5 Gitzo tripods. Manfrotto makes two levelling bases (the 3502, plus another one that might be discontinued) that can be attached to a 3/8 in. tripod screw. I tried both, and was not impressed with either one. In particular, the 3502, which looks like a squashed ball head, has rather rough surfaces and a tendency to collect grit, which makes its movements jerky.
All levelling bases allow only limited movements (typically, a maximum adjustment range of 10 to 15 degrees from the horizontal), and this means that in the field the length of the tripod legs should be adjusted as a first approximation, and the levelling head used afterwards. Most Gitzo series 3 and series 5 tripods have bubble levels to help with the first, rough adjustment.
Needless to say, the 501 should not be used on top of a tripod central column (except possibly very large video columns, or studio camera supports). In fact, I have found by experience that tripod columns should be avoided whenever vibration of a tripod is a concern.