Observation Chair

Observation Chair

My observation chair is a mildly modified version of The Denver Observer's Seat, developed by David Trott and Charles Carlson of the Denver Astronomical Society.

Before having this chair, I was using a 3-legged Ikea stool, turning the seat around to adjust its height. The stool was functional but inconvenient when height adjustments were frequently required during observation.

This chair is very straight forward to make and is one of the most useful accessories I have ever made. It makes star gazing much more comfortable and enjoyable.

This chair is very sturdy but a little bit too heavy when you need to lift it frequently. In the future, I will make a light-weight version of this chair, the frame will possibly be made of aluminium instead of timber.

The detailed plan and description of The Denver Observer's Seat can also be found in Phil Harrington's Star Ware 2nd Edition. James Crombie (ChairJim) has his version of Ajustable Observing Chair design plan published on his web site.

The CATSPERCH Observing Chair by Jim Fly is another good design to consider if you do not want to make your own chair.

Click on the thumbnails below to see larger pictures.

		Sawing the timber to 22.5 degrees with the aid of a mitre box.
		Timber painted with several coats of instant Estapol.
		Frame assembled with cross-bars. The original design only has one cross-bar at the front. I chose to have cross-bars at both front and back because the thickness of the material I had was less than the original specification. I think it also helps improving the stablity of the chair, although not really necessary.
		The frame joined with a door hinge.
		The cross-bars are glued and bolted to the frame.
		Self-adhesive anti-skip stripes (outdoor grade) at the front of the frame. They are like very strong sand paper on rubber base. Anti-skip stripe is also applied on the front cross-bar.
		Cross-brace is made of alumium. Only one is really needed but I chose to have two to hold the frame more rigidly (see the fully assembled photo below).
		Handle for carrying the chair while in the field. The handle also overlaps the anti-skip stripes to stop them from peeling off. Since the rear cross-bar balances the chair quite well, the handle could have been installed at the rear frame instead.
		Fully assembled.
		Seat frame. I used a thick cardboard as spacing before assembling one of the side panels to the supporting timber. The spacing must be thick enough so that the seat can slide up and down easily.
		Seat frame asembled. I assembled the seat before painting it and later discovered that the spacing is a not quite enough due to the thinkness of the Estapol.
		Bolt holding the seat against the chair frame. Do not over-tighten the nut otherwise the seat cannot slide smoothly along the chair frame. The bolt chosen must be strong enough to hold your weight!
		In order to achieve maximum friction when in contact with the anti-skip stripes, the rear side of the seat is glued with a piece of black rubber sole.
		Garden-hose covering the bolt to protect the timber frame.
		The chair folded and ready to be transported. Since the frame of the chair is made of solid timber, it is a bit on the heavy side. If I am going to make another one, I will re-design the frame to trim off some weight.
		The seat at normal height. After the first beta testing of the chair, I have taken a friend's advice to round off the front corners of the seat. A thin foam (camping-matt) is also added to make sitting more comfortable.
		The seat at maximum height.
		The seat at minimum height. At this height the bluk of weight is concentrated at the front so it is possible for the chair to tip forward, lucky the seat is not too far from the ground.
		The Chair in the field.
		Another angle of the chair in the field.

Amateur Astronomy