A Cautionary Undercut Tale

[Nightspore]

Recently I’ve been testing various 2” eyepieces in some of my 2” diagonals. Most of my diagonals either have a 'Fast Lock' type or are Baader ClickLocks.

 

 

The Fast Lock type has rods inside the draw tube which engage the eyepiece barrel when the lock is twisted. As a further measure the lever itself can be threaded in as an extra safety lock.

 

 

The lighter Baader ClickLock mechanism uses a compression ring type 'collet' instead of rods and has no safety lock.

 

 

The rods can be seen in the Fast Lock type below:

 

 

Most 2" eyepiece barrels work in either type. However, my 19mm Celestron Luminos has never been totally secure in the Fast Lock type and required the safety lock.

 

 

Unfortunately when I recently tried the Luminos in the Baader ClickLock it became stuck fast.

Luckily this was during indoor weight and balance trials and not outside in the night. I rarely used the Luminos in the

Baader dielectric and it was quite disconcerting to have it inextricably stuck in the ClickLock.

 

 

Eventually I had to unthread the ClickLock mechanism from the diagonal housing and also unthread the Smyth barrel from the Luminos. No mean feat considering I am partially paralysed in my right arm and hand. The slight scoring on the Luminos barrel as a result of this activity can be seen in the above pictures. The Luminos undercut is almost certainly the culprit as I've never had any 2" eyepiece stuck in a Baader ClickLock before.

Edited June 27, 2020 by Nightspore
Don't get me started ...

[+Derbyshire Dave]

Sounds scary. Appreciate you sharing 

[Nightspore]

6 hours ago, Derbyshire Dave said:

Sounds scary. Appreciate you sharing 

I know undercuts are a problem, but this was totally unexpected. And scary lol.

[+Bino-viewer]

I've never had an issue with a compression ring on a smooth barrel (eyepiece or diagonal)

 

I've had lots of issues with compression rings on an undercut type design.

And as for tapered eyepiece barrels, don't even go there.....😀

[Nightspore]

2 hours ago, Bino-viewer said:

I've never had an issue with a compression ring on a smooth barrel (eyepiece or diagonal)

 

I've had lots of issues with compression rings on an undercut type design.

And as for tapered eyepiece barrels, don't even go there.....😀

Slight tapers seem to be less problematical than undercuts. The 19mm Luminos stuck in the Baader dielectric was a bit of a shock. Several years ago I got a 17mm Celestron (Barsta) Plossl stuck in a Tele Vue 3x Barlow for something like half an hour. I just couldn't figure what had gone wrong.