Newtonian Secondary

[Hans Tucker (Hans)]

Purchase my first Newtonian (Orion UK VX10" f4.8) a while back and it came with the secondary removed for safe transport. I am fitting the secondary to the spider holder with a M5 centre screw. The three collimation screws are M4 I think. Question is how far do you screw down the centre mounting screw, obviously the secondary must pivot on this screw in order for the collimation screws to take effect. How stable is this and will it hold collimation. Has anyone put a short spring between the secondary holder and the spider mount to put tension on the centre screw?

[glend (Glen)]

The centre screw is usually the secondary offset screw, and is only used to move the secondary fore or aft to align under the focuser tube. Most fast newts have varying range of offset. I suggest you read Asttobaby's collimation guide, as it covers offset. There is also a formula for calculating the required offset, but I can't remember it.

[N1 (Mirko)]

Collimation will dictate its position. Secondary must appear circular through the focusser while seeing all of the primary.

[Startrek (Martin)]

Before you fit the secondary cut a piece of plastic from an empty milk bottle in the shape of the secondary stalk ( oval ) and place it between the stalk base and spider
This will assist in preventing the 3 adjustment screws from pitting or gouging out the secondary base which is alloy type material
I’ve done this to all my newts and also gives you more feel when collimating the secondary ( found this little mod on CN )
It works a treat

[Startrek (Martin)]

Sorry details below -

Just type in Cloudy Nights Milk Jug Washers ( Jason D )

There’s a diagram and procedure how to make one

Cheers