5 replies to this topic

[bigbangbaby]

I use Astrosystems secondary holders in all my Newtonians. They are lightweight and securely hold the mirror. Problem is, the plastic body on which the adjustment screws bear is soft and easily deforms. Over time, the plastic yields and the secondary collimation is lost. 

 

Some designs place a compression spring under the center stud. Tightening the adjustment screws compresses the spring and limits load on the plastic. I chose instead to bond (with 3M 77 spray adhesive) a thin metal disc onto the plastic surface. I placed a small square of duct tape for one of the screws to touch. Tightening this screw creates a small divot in the tape, which prevents the secondary holder from rotating about the center stud.

 

During collimation, I snug each screw against the metal disc. The screws firmly tighten rather than feel squishy as before. The primary holder has lock screws to secure mirror position. With the enhancement to the secondary holder, the scope should hold collimation better than it did. 

 

Installed in my Meade 826

 

Steel disc

Edited by bigbangbaby, 17 May 2025 - 02:38 PM.

[bigbangbaby]

BTW, the steel disc is something that I had laying around. It’s plated carbon steel and a bit crusty. I thought of sanding and painting it flat black, but it would have gotten scratched up anyway. I cleaned it with lacquer thinner before bonding it to the plastic shell. 

[RLK1]

I have a 16" astrosystems f4.5 dob I've been using for decades and I've never encountered any difficulties with anything deforming, including any components in the spider assembly. I don't think the part in question is plastic although I'm not certain of its composition but I've not seen/experienced any issues with it in my rig or in similar telekits I've seen in the field.

 

That said, astrosystems spiders are well-regarded and are utilized not only in the telekits but also in other premium scopes built by other makers. 

[bigbangbaby]

I have a 16" astrosystems f4.5 dob I've been using for decades and I've never encountered any difficulties with anything deforming, including any components in the spider assembly. I don't think the part in question is plastic although I'm not certain of its composition but I've not seen/experienced any issues with it in my rig or in similar telekits I've seen in the field.

 

That said, astrosystems spiders are well-regarded and are utilized not only in the telekits but also in other premium scopes built by other makers. 

Take a look where the collimation screws push against the plastic secondary hub, the part to which the stud passes through and the aluminum shell screws to. Notice the divots. That’s what this steel disc fixes. High-end Newtonians typically use aluminum secondary hubs. The Astrosystems spiders are decent quality.

[RLK1]

Take a look where the collimation screws push against the plastic secondary hub, the part to which the stud passes through and the aluminum shell screws to. Notice the divots. That’s what this steel disc fixes. High-end Newtonians typically use aluminum secondary hubs. The Astrosystems spiders are decent quality.

Divots can/do occur because the collimation knobs are being pushed in too hard when the wing nut is tightened too much. The way to avoid any potential for this to occur is to simply loosen the wing nut while all of the collimation knobs are parallel at their push points against the plate. Then tighten the wing nut and collimate with the knobs as usual. This produces equal contact pressure at the back of the plate and prevents  indentions. 

[bigbangbaby]

Plastic can and does creep over time, especially under a point load as is applied by the tip of a collimation screw. I’m glad you find it satisfactory as is. I saw room for improvement.