A small increase in tube diameter can have a significant effect on stiffness (cube law), so I have always fully extended the top tube sections of my tripods and adjusted the required height via the bottom tubes.
However, I think I now have to revise that advice.
Another tripod thread prompted me to take a closer look at collet (twist) locks. I dismantled the second 32 mm leg section of an old Gitzo Studex and after reassembly was surprised to find that it could be displaced when fully extended although the collet was firmly tightened. I repeated this with my Sirui and Novoflex carbon fibre tripods with similar results. It's very noticeable if you lay the tripod horizontally on the floor and apply a lateral load to the extended second tube.
Recent carbon fibre tripods generally have a mere 3 mm difference in diameter between adjacent tube sections and 1mm wall thicknesses (sometimes more for very thick tubes) so the interference fit is accomplished by 0,5 mm thick and 3 cm long half shells at the tops of the tubes.
The tubes have two internal rails about 0,4 mm high to guide the gaps between the half shells and prevent the tube rotating when the clamp is loosened. This enables one to open or close all clamps simultaneously when the tripod is collapsed.
Previously, as on the old Gitzo Studex, it was necessary to unlock from bottom to top and lock from top to bottom. This procedure is still advisable with modern tripods to avoid putting too much torque on the thin shims and rails.
Bicycle seat posts have a recommended minimum insertion depth in the frame's saddle tube for obvious reasons. Tripod legs only overlap by about 6 cm when fully extended and I think something like an additional 5 cm is necessary for a rigid joint.
It would be unrealistic to expect manufacturers to restrict tube extension in the interests of rigidity and thereby sacrifice their maximum height specifications, and it's going to be tedious setting up a multi-section tripod for an additional 5 cm overlap at each joint. I have put pencil marks on mine and am now almost grateful for the markers on my Novoflex TrioPod, which I criticized in my review.
In summary this is just another argument for restricting the number of tripod sections and doing without a centre column.
John
However, I think I now have to revise that advice.
Another tripod thread prompted me to take a closer look at collet (twist) locks. I dismantled the second 32 mm leg section of an old Gitzo Studex and after reassembly was surprised to find that it could be displaced when fully extended although the collet was firmly tightened. I repeated this with my Sirui and Novoflex carbon fibre tripods with similar results. It's very noticeable if you lay the tripod horizontally on the floor and apply a lateral load to the extended second tube.
Recent carbon fibre tripods generally have a mere 3 mm difference in diameter between adjacent tube sections and 1mm wall thicknesses (sometimes more for very thick tubes) so the interference fit is accomplished by 0,5 mm thick and 3 cm long half shells at the tops of the tubes.
The tubes have two internal rails about 0,4 mm high to guide the gaps between the half shells and prevent the tube rotating when the clamp is loosened. This enables one to open or close all clamps simultaneously when the tripod is collapsed.
Previously, as on the old Gitzo Studex, it was necessary to unlock from bottom to top and lock from top to bottom. This procedure is still advisable with modern tripods to avoid putting too much torque on the thin shims and rails.
Bicycle seat posts have a recommended minimum insertion depth in the frame's saddle tube for obvious reasons. Tripod legs only overlap by about 6 cm when fully extended and I think something like an additional 5 cm is necessary for a rigid joint.
It would be unrealistic to expect manufacturers to restrict tube extension in the interests of rigidity and thereby sacrifice their maximum height specifications, and it's going to be tedious setting up a multi-section tripod for an additional 5 cm overlap at each joint. I have put pencil marks on mine and am now almost grateful for the markers on my Novoflex TrioPod, which I criticized in my review.
In summary this is just another argument for restricting the number of tripod sections and doing without a centre column.
John
