Requests for advice on tripod purchase are often posted on birdforum and frequently I am surprised that birders are prepared to spend large sums on a scope but try to scrimp on a tripod and head.
A scope not only magnifies the subject but it also magnifies angular disturbances. With an inadequate tripod it only requires a touch on the focusser or a moderate breeze to make viewing impossible.
A frequent contributor on this forum has often stated that a stable tripod is more important for a scope than a camera. If one considers that a 600 mm lens only has a 12x magnification compared to a 50 mm standard full-format lens and that scopes are often used at 50-70x magnification, I think he has a very valid point. Also, a shutter is only open for a small fraction of a second but a scope is used for extended viewing.
So here are some of my experiences and prejudices
:-
Materials:-
There are four common materials used for tripods, wood, aluminium, basalt fibre reinforced plastic and carbon fibre reinforced plastic. Magnesium alloy is sometimes used for castings. It's lighter than aluminium but less stiff, so you have to use more of it.
Wood (usually ash) is relatively light and, being solid has high internal damping so vibrations subside quickly. Wooden tripods are popular with surveyors, sea watchers and amateur astronomers. They are moderately priced but heavier than comparable cabon fibre tripods.
Aluminium is inexpensive but has poor internal damping and will vibrate longer. It is also very cold to the touch in winter With large diameter tubes the amplitude of the vibrations can be kept within acceptable limits but the tripod will be heavy.
Basalt fibre was introduced by Gitzo as a compromise on weight, stiffness and cost between aluminium and carbon fibre. Its mechanical properties are very similar to glass fibre. Pole vault poles are made largely of glass fibre and are intended to store energy and then release most of it - not what we want for tripods. I have a (rather expensive) basalt tripod, which proved inadequate even at 30x on a windy coastline. It has now been relegated to use with binoculars.
Carbon fibre, compared to the other materials is light and extremely stiff. Its vibration damping is not particularly good but if one has to carry the scope and tripod longer distances it is the ideal (and most expensive) material. Due to the low density and strength of CF reinforced plastic, the weight penalty for increased stability is not that high. A 150 cm tripod with 28-36 mm leg sections can be kept under 2,5 kg.
Dimensions:-
Taking eye position, the height of the tripod head and the scope into account, one could say that the minimum tripod height should be one's own height minus 30 cm for a straight scope or minus 50 cm for an angled scope. The number of leg sections should be kept to a minimum compatible with transport requirements, less because of any potential instability in the joints, but because increasing number of sections leads to thinner bottom sections. The rigidity of a tube of a specific material is proportional to the tube thickness and to the cube of the tube diameter. A 32 mm tube is therefore eight times stiffer than a 16 mm tube and even a 20 mm tube is about twice as stiff. I would consider the latter to be an absolute minimum for the bottom leg sections of a carbon fibre tripod. I prefer twist locks to clip locks as the former are self-adjusting. Most modern tripods also have internal rails to enable simultaneous opening or locking in the closed position. It is often suggested that one should not extend the centre column or do without one completely, but it is a convenience and with a dianmeter often the same as the top leg sections is IMO not such a severe detriment to stability if used moderately. If one hangs a back pack on the hook under the centre column it should have ground contact, otherwise the tripod will oscillate with pendulum frequency. Vibrations can also be damped effectively by hanging the strap of a loaded binocular bag over all three legs.
Heads:-
Video (2-way) heads are ideal for scope use, preferably of all metal construction and with a minimum load rating of 5 kg or 6 kg. A preload function for the tilt is useful to prevent the scope crashing into the top of the tripod. The top disc of some tripods has an off-centre grub screw, which will prevent inadvertant loosening of the head. Not the optimum solution, but it is also possible to use a ball head as a 2-way head if one drops the spindle into the slot and rotates the scope in its collar by 90°.
Quick Release Sytems:-
QR plates should preferably not have rubber surfaces as these introduce compliance. An anti-rotation pin or pins to prevent loosening of the plate is also mandatory. The Arca-Swiss system is to be favoured, being universal. However, the safety retention of Arca-Swiss plates often differs from one make to another, so it is advisable to stay with one manufacturer. Long plates are required to balance some scopes or when digiscoping.
Lastly, I favour using 3/8"x16 threads and avoiding the use of 1/4" to 3/8" adapters.
Comments welcome.
John
A scope not only magnifies the subject but it also magnifies angular disturbances. With an inadequate tripod it only requires a touch on the focusser or a moderate breeze to make viewing impossible.
A frequent contributor on this forum has often stated that a stable tripod is more important for a scope than a camera. If one considers that a 600 mm lens only has a 12x magnification compared to a 50 mm standard full-format lens and that scopes are often used at 50-70x magnification, I think he has a very valid point. Also, a shutter is only open for a small fraction of a second but a scope is used for extended viewing.
So here are some of my experiences and prejudices
:-Materials:-
There are four common materials used for tripods, wood, aluminium, basalt fibre reinforced plastic and carbon fibre reinforced plastic. Magnesium alloy is sometimes used for castings. It's lighter than aluminium but less stiff, so you have to use more of it.
Wood (usually ash) is relatively light and, being solid has high internal damping so vibrations subside quickly. Wooden tripods are popular with surveyors, sea watchers and amateur astronomers. They are moderately priced but heavier than comparable cabon fibre tripods.
Aluminium is inexpensive but has poor internal damping and will vibrate longer. It is also very cold to the touch in winter With large diameter tubes the amplitude of the vibrations can be kept within acceptable limits but the tripod will be heavy.
Basalt fibre was introduced by Gitzo as a compromise on weight, stiffness and cost between aluminium and carbon fibre. Its mechanical properties are very similar to glass fibre. Pole vault poles are made largely of glass fibre and are intended to store energy and then release most of it - not what we want for tripods. I have a (rather expensive) basalt tripod, which proved inadequate even at 30x on a windy coastline. It has now been relegated to use with binoculars.
Carbon fibre, compared to the other materials is light and extremely stiff. Its vibration damping is not particularly good but if one has to carry the scope and tripod longer distances it is the ideal (and most expensive) material. Due to the low density and strength of CF reinforced plastic, the weight penalty for increased stability is not that high. A 150 cm tripod with 28-36 mm leg sections can be kept under 2,5 kg.
Dimensions:-
Taking eye position, the height of the tripod head and the scope into account, one could say that the minimum tripod height should be one's own height minus 30 cm for a straight scope or minus 50 cm for an angled scope. The number of leg sections should be kept to a minimum compatible with transport requirements, less because of any potential instability in the joints, but because increasing number of sections leads to thinner bottom sections. The rigidity of a tube of a specific material is proportional to the tube thickness and to the cube of the tube diameter. A 32 mm tube is therefore eight times stiffer than a 16 mm tube and even a 20 mm tube is about twice as stiff. I would consider the latter to be an absolute minimum for the bottom leg sections of a carbon fibre tripod. I prefer twist locks to clip locks as the former are self-adjusting. Most modern tripods also have internal rails to enable simultaneous opening or locking in the closed position. It is often suggested that one should not extend the centre column or do without one completely, but it is a convenience and with a dianmeter often the same as the top leg sections is IMO not such a severe detriment to stability if used moderately. If one hangs a back pack on the hook under the centre column it should have ground contact, otherwise the tripod will oscillate with pendulum frequency. Vibrations can also be damped effectively by hanging the strap of a loaded binocular bag over all three legs.
Heads:-
Video (2-way) heads are ideal for scope use, preferably of all metal construction and with a minimum load rating of 5 kg or 6 kg. A preload function for the tilt is useful to prevent the scope crashing into the top of the tripod. The top disc of some tripods has an off-centre grub screw, which will prevent inadvertant loosening of the head. Not the optimum solution, but it is also possible to use a ball head as a 2-way head if one drops the spindle into the slot and rotates the scope in its collar by 90°.
Quick Release Sytems:-
QR plates should preferably not have rubber surfaces as these introduce compliance. An anti-rotation pin or pins to prevent loosening of the plate is also mandatory. The Arca-Swiss system is to be favoured, being universal. However, the safety retention of Arca-Swiss plates often differs from one make to another, so it is advisable to stay with one manufacturer. Long plates are required to balance some scopes or when digiscoping.
Lastly, I favour using 3/8"x16 threads and avoiding the use of 1/4" to 3/8" adapters.
Comments welcome.
John
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