Introduction:

The idea for a 'barn door' mount has been acredited to George Haig(1). Perhaps not too surpisingly 'barn door' mounts are also known as a 'Haig' mounts or even as 'Scotch' mounts.

There have been many practical versions of the barn door, some very simple, some not so simple. A basic barn door mount consists of the following:

1.Two flat boards, connected by a hinge.
2.An angled block of wood or photographic tripod to support the lower board at an angle corresponding with local latitude.
3.A ball and socket camera mount fixed to the upper board.
4.A threaded nut and bolt arranged so as to be able to drive the two boards apart.

In essence, that's it! There's a bit of design work needed to define optimum dimensions, but it's not rocket science and need not stretch DIY skills too far.

So let's have a look at some practical implementations.

Stephen Tonkin discusses the design, materials list, construction and use of a basic manually driven barn door.

Dave Gavine describes a basic barn door and a clockwork 'leerie'. Some more history here.

Geoff Johnstone's barn door is described in the Instruments And Imaging section of the BAA.

Harry Ford provides a variant which does away with hinged panels in favour of sliding panels connected via a solid bolt. Harry also recalls meeting George Haig.

Doug Miller shows lots of animated pictures of a motorised barndoor, but is lacking in detail.

Alan Jefferis describes a mount driven by an ordinary (ie not a stepper) motor used in combination with an electronic timer/microswitch system. Uses standard Maplin parts.

Mike Anttila describes a stepper motor driven, PC controlled barn door. This is a relatively recent article which refers to the use of Windows XP.

Depending on the focal length of the camera lens used, simple basic barn door mounts can provide practically accurate tracking for periods of up to 5 or 10 minutes. Because of the geometry of the barn door, tracking errors then become increasingly significant. Stephen Tonkin discusses the limitations/errors inherent in conventional barn doors and descibes a more accurate 'double arm' design.

Tracking errors inherent in a basic barn door can be elliminated by use of a radially curved drive bolt. This is described by Dean Ketelsen. I used this principle in one of my own barn doors, as discussed later.

Another curved bolt design is described by Philippe Chretien

For a fuller listing of articles relating to barn doors, try 'Googling' for 'barn door mount'.


Motor Drive?

The simplest barn door mounts are manually driven. If the design is such that exactly one complete rotation of a hand wheel is required per minute, then it's quite easy to mentally 'keep track' of the tracking. Addition of a motor drive can make operation even easier. Refer to the section entitled Motors for further information.

Ref.(1) George Haig, Sky & Telescope, April 1975