Macro tubes help please

Quote:
The KAF mount features the same six electric contacts as the KA, and thus remains fully compatible with the older mounts. However, in addition to those (electric) contacts, it features a seventh — electronic one. Using a yet-unknown serial protocol, the body uses this contact to communicate with a digital chip contained inside the lens housing. The chip provides at least the following information:
- Focal length of the lens. This allows more efficient flash operation as well as calculating the longest hand-holdable shutter speed. In addition, it is also one of the parameters taken into account when the body is in one of the "smart" picture modes and has to choose a program curve. Prime lenses provide one fixed value, while zooms provide an approximate value that changes as the focal length changes. The focal length information is precise enough to distinguish between 35, 28 and 24 mm lenses, as evidenced by F-flashes that trigger a warning when they cannot cover the field of view of the lens.
- Lens-to-subject distance. This is used by the more advanced bodies for calculating if the flash is powerful enough to illuminate the subject that is in focus. In addition, this is one of the parameters taken into account when the body is in one of the "smart" picture modes and has to choose a program curve.
Exact selected aperture. The KA mount supports displaying the picture-taking aperture when the "A" aperture setting is engaged. The KAF mount supports displaying the aperture even when a numeric f-stop is selected. The displayed value is quantized by half-stops, but is correct even when a variable-aperture zoom lens is used.
- Lens dimensions. The lens also gives the body enough information for determining if the lens is going to cast a shadow on the subject when the camera's built-in flash is used. This parameter takes into account the size changes due to zooming and focusing too.

The lenses contain a ROM chip that holds the program curve (brightness/shutter speed/aperture) for prime lenses or up to three program curves for zooms at their different focal length settings. The distance information is hardwired on the lens barrel. A number of tiny parallel conducting/non-conducting strips are glued to the rotating part of the lens. The same number of contacts are attached to the fixed part of the lens. As the lens barrel turns during focusing, different combinations of the strips are detected by the contacts. There are four parallel strips in the F 50/1.7, resulting in at most 16 different distance settings. But for that particular lens not all combinations are used.

A similar technique must be used for the focal length.

gartmore wrote:
I have a set and a K20, you dont get focal length information but the scratching, I think just creates anothe contact to the mount itself. You'll need to do a search but I think Mannesty was the original brains behind this.