PST - how much force?

[dasilvor]

Hi,

I have a six month old PST, which I would like to modify. I attempted to unscrew the gold tube from the etalon, (using hand force only to start with). The trouble is the whole unit then unscrewed from the black box section, leaving the etalon and 40mm objective still attached to the gold tube. There was no lock tight on the thread.

Because of the lack of space available, the force is now going to have to be applied to the etalon focusing ring to get it to unscrew from the gold tube.

So, how much force can I apply to the etalon to get the gold tube to release?

Cheers

Dave

[misterp]

Hi Dave,

I have just modded my pst. The gold tube came off the etalon easily on mine however I put it back on and removed the objective lens and used the gold tube in my mod.

HTH

Ian

[Merlin66]

Do you have a copy of my PST Mods write -up?

You sometimes need a couple of good BOA straps and a fair amount of force.

Just a quick "crack" sometimes gets them going....

[Photosbykev]

Be aware that all the torque will be going through a small end stop screw inside the tuning ring which might be damaged by too much load. If you slide the rubber band off the etalon you will see the screw, this just locates in one of a number of plain holes under the tuning ring.

[dasilvor]

Merlin66, I have a version of your writeup. what is the latest version, please?

Kev, this is what I am worried about. The only point I can apply force to is the etalon adustment ring, and I don't want to ruin the whole scope by breaking the adjustment of the etalon.

I think I will try to get the objective off as Ian has. Failing that I will give it a try with a couple of BOA straps, but it will be done gently. Fingers crossed.

Dave

Ps thank you all for the replies, though.

[Peter Drew]

If you remove the objective you can use the complete rest of the PST assembly as a Ha eyepiece slid into a 2" fit focuser. The "gold" tube is nominally 50mm o/d so you will need to pack out a portion next to the etalon tuning ring to make it fit. Using this method allows you to quickly rebuild the original PST for grab and go use.

[Photosbykev]

If you remove the endstop screw you can remove the outer tuning ring, it

just slides off. Mark up the rings so that you put the screw back into the

same hole on reassembly.

With the ring removed you can apply more torque with a BOA on solid metal.

[Merlin66]

I've dismantled many PST's, some with joins flooded in Locite..it can be done!

If you haven't seen any visible loctite yet, then I'd guess it may be just "fear of the unknown" - as Kev say's you can remove the adjuster - I've never seen an etalon damaged during removal.

(All this is covered in the available PST Mod write-up - PM an email address for a copy)