Last Updated June 24, 2002
Here are some photos of my first scope project. I've updated this scope with several improvements and the following is my latest rendition of this scope. The mirror is an f5.13 curve (hand made ) using 2.25" thick Pyrex glass. As you scour the web you'll see many wonderful two truss scope designs. The interesting areas of my design are the use of a round secondary cage with only two trusses. The focuser is also kind of unique in that it is a Helical Crayford clone. I've provided a link to a page for it as well.
Here are the pictures:
Click on the photos to see close ups.
The following photos are of the packed up scope. Packed up it measures 18"x18" by 21" high. The secondary cage fits inside of the mirror box for easier storage and transport. The white material is a tight mesh nylon material similar to that used for tents.
These are close ups of the secondary cage. The cage weighs about 3 lbs (without eyepiece) and has a balance point about 1" of the inside edge of the poles to limit pole deflection. The first photo shows top and bottom clamps used to tighten up the cage onto the poles to prevent slippage of the secondary cage down the poles. I can easily adjust the secondary cage position in the event I need to move further or closer to the primary. The secondary mirror is heated via two of the 4 spider vanes. The power is supplied by the telerad batteries and can be switched on or off by the switch shown in the first photo below. The sides are 3/8" Baltic Birch plywood supported by 1/2" dowels glued and screwed together. The focuser board is placed on top of two dowels and glued in place. The outer shroud is a very thin sheet of blackened Lexan which has been attached via silicone.
Here are photos of the scope setup and ready to use. I used exercise weights over the poles to quickly adjust the balance point as needed. This is a very simple idea which works perfectly. The Teflon pads provide buttery smooth motions. The poles are 2" OD 0.065" wall thickness and are about 5' long. They are stable and collimation is retained fairly well. The total weight of the scope is about 70 lbs (22 lbs mirror, 20 lbs mirror cell, 17 lbs wood, 3 lbs secondary cage, 5 lbs poles, 3 lbs telerad, weights, etc).
Here is a photo of the back side of the scope. The mirror cell is a standard 9 point cell built precisely to Kriege's guidelines. Works well but is nearly 20 lbs. I think I'll use aluminum next time. The fan doesn't seem to do much because the mirror is so thick. My next improvement will be to cross cool the front surface of the mirror as outlined in a Sky and Tel article last year.
In summary I'm really happy with the performance of the scope.
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