About lens bridges and tripod props
I have found in recent years, that an animal picture turns out so much better if I pulled the section up closer: either by going in closer, using a different lens with a longer focal length or through the addition of a telephoto converter. The last of these being the better method since the animal is normally not very pleased about further approaches that impair its privacy, an even longer focal length is usually not available, a change of lens would take too much time but a converter is slipped on easily and quickly enough.
From a pure technical point of view, one could actually say that todays new converters of well known manufacturers are so good, that you can hardly tell a photo taken with a 1,4x converter from one taken without a converter. A picture taken with a 2x converter looses about 10-20% in quality, but it is definitely good enough to use as a publication.
If pictures taken with a converter turn out to be drastically worse, it does not necessarily have something to do with the converter. The loss of 1-2 aperture stops lengthens the exposure automatically: If you had 1/500 sec with an open aperture, you will have only 1/250 sec or 1/125 sec with a 1,4 x or 2 x converter, with the same f-stop on the lens.
Then you will find exact focusing more difficult with a dark focusing screen: you have to work more careful. Because now you have a 8.0/600 mm lens when using a 4.0/300 mm lens with 2x converter.
Additionally, you will find that through the converter, the camera is more distanced from the tripod clamp and in turn brings vibrations to have greater effect. So in order to have sharper pictures even with converters, you need to work more careful and avoid the unnecessary movements of the camera which result when pushing the shutter release, by using a sturdy tripod and a good head bearing.
In doing so, there are ways of supportive action you can take to avoid these compounded vibrations, for instance by using one or both accessories: a lens bridge and/or a tripod prop.
These two accessories have two functions: first, to support stability and second, you can put the unit lens-converter-camera in a totally balanced position so as to avoid any top-heaviness no matter which converter at that moment is being used and however heavy the camera casing is. There is a big difference if you have a F90x or a F5 attached to the converter and the center of gravity in this unit would be changed enormously. The picture to the left above shows the equipment with the AF-Nikon 4.0/500 mm, but without the converter; the one in the center with the 2x converter. On the position of the tripod clamp above the wheel lock from the quick slip plate, you can clearly see the balance points of the different units. To the right the equipment with the additional tripod prop. If you´re sure to take only horizontal shots, then the highest stability is guaranteed if you fasten the tripod prop the fourth tripod leg so to speak under the camera casing. If you need to switch from horizontal to vertical shots, you should fasten it on the end of the lens bridge.
The purpose of the lens bridge is to restore the stability of the unit lens / camera from vibrations, since the stability was reduced by the extension with the converter.
With the 2x converter you should additionally use whenever possible a tripod prop, because a heavy camera like for instance the Nikon F5 or the EOS-1 with the motor is relatively far distanced to the tripod clamp and if you tap the casing of a long unit like a 500 mm lens with 2x converter and camera on a sturdy tripod with adequate head you would be surprised to see the resulting vibrations. These can be minimized with these two supportive accessories.
Documentation on the above discussed accessories can be obtained from the manufacturer : Rainer Burzynski, (special equipment for wildlife photography), Tel.: +49-39856-3061 or Fax.: +49-39856-3062.