How I dealt with the undercuts

[JeremyS]

Various people have been banging on about undercuts on eyepieces - well mainly me, actually 😊

People have come up with a number of solutions to this engineering nightmare (sorry, John 😊).

I have been trying one suggested in a video by Danial Mounsey. This is to use parfocalising rings. Certainly worked in my tests with various TV eyepiece ps in my Tak diagonal last night. I had a pack of 4, which I’ve now installed on 4 EPs as in the pic. Another pack of 4 on order for the remaining EPs

🤞🏻
 

as an aside, I confirmed that not all the undercuts are the same design as @Alan White pointed out on another thread 🤔

 

Edited August 26, 2021 by JeremyS

[jetstream]

@JeremyS Excellent solution!

[jetstream]

AND!

I really want the one on the bottom left.

[John]

Nice approach Jeremy

I have used a parfocalising ring with my Nagler 2-4 zoom and Panoptic 24 but that was to make them closer to par focal with my Pentax XW's rather than to mitigate the effects of the undercut.

I can't recall when Tele Vue changed the design of their undercuts. My collection contains both styles.

I'm using my Ethos set this evening with my 12 inch dob so I promise that I will be VERY careful with the drawtube insertion / removal process

If I snag one on an undercut and drop it onto the patio, I'm in for some very large portions of humble pie !

 

[JeremyS]

1 minute ago, John said:

Nice approach Jeremy

I have used a parfocalising ring with my Nagler 2-4 zoom and Panoptic 24 but that was to make them closer to par focal with my Pentax XW's rather than to mitigate the effects of the undercut.

I can't recall when Tele Vue changed the design of their undercuts. My collection contains both styles.

I'm using my Ethos set this evening with my 12 inch dob so I promise that I will be VERY careful with the drawtube insertion / removal process

If I snag one on an undercut and drop it onto the patio, I'm in for some very large portions of humble pie !

 

Good luck John. At least they don’t contain any of that self vaporising and dissolving fluorite stuff 🤣👍🏻

[Louis D]

I tried that approach with my 12mm NT4's 2" skirt with extension, but where the parfocalization ring needed to go was right on the lower taper, so it wanted to slide into the taper as I tightened it.  I ended up going with rubber O-rings instead:

[JeremyS]

I think I’m falling in love with my Naglers again. Or at least with the ones with the rings.  👍🏻

[markse68]

is there a danger that by effectively removing the upper 1.25” part that when you tighten the clamp screw the ep will be pushed over at an angle in the focuser? I guess if you’re using a click lock type band clamp it wouldn’t be and would depend on clearance in focuser tube otherwise.

Mark

[Captain Scarlet]

Are the nosepieces simply threaded into the bottom of the eyepiece body? In which case one could just unscrew them and replace with non-undercut nosepieces (keeping the originals aside and pristine for when the eyepiece needs to be moved on)?

[JeremyS]

55 minutes ago, Captain Magenta said:

Are the nosepieces simply threaded into the bottom of the eyepiece body? In which case one could just unscrew them and replace with non-undercut nosepieces (keeping the originals aside and pristine for when the eyepiece needs to be moved on)?

Not properly investigated Magnus for fear of all the lenses dropping out. The barrel does seem to unscrew, but it also comes with the base plate attached. Not comfortable with going further.

[Alan White]

43 minutes ago, JeremyS said:

Not properly investigated Magnus for fear of all the lenses dropping out. The barrel does seem to unscrew, but it also comes with the base plate attached. Not comfortable with going further.

You are not prepared to take one for the team, tsk, tsk Jeremy 🤣
The resulting thread of 'Where do these lenses go?' would keep so many of us interested in any misfortune you might befall.
I must point out I am not encouraging you to pull apart fine kit in anyway, i jest.

[Captain Scarlet]

1 hour ago, JeremyS said:

Not properly investigated Magnus for fear of all the lenses dropping out. The barrel does seem to unscrew, but it also comes with the base plate attached. Not comfortable with going further.

Fair enough; I also haven't dared for similar reasons

[Louis D]

13 minutes ago, Captain Magenta said:

Fair enough; I also haven't dared for similar reasons

Most eyepieces I've dealt with use the lower base plate to hold the eyepiece lenses in place in lieu of a separate retaining ring, so caveat emptor.

Edited August 27, 2021 by Louis D

[johninderby]

One of the newer type of twist lock adaptors solves the undercut problem by using a nice wide clamping band. Similar wide bands used on some 2” diagonals now as well.

Edited August 27, 2021 by johninderby

[Don Pensack]

6 hours ago, markse68 said:

is there a danger that by effectively removing the upper 1.25” part that when you tighten the clamp screw the ep will be pushed over at an angle in the focuser? I guess if you’re using a click lock type band clamp it wouldn’t be and would depend on clearance in focuser tube otherwise.

Mark

The answer to your question is yes.  The small 1.25" section at the top is necessary to be inserted in the focuser so the eyepiece doesn't tip.

And your assumption about Click-Lock and Twist-Lock attachments is correct.

[John]

In many eyepiece designs the 1.25" barrel assembly also holds one or more of the lens elements in place. In long eye relief and wide angle eyepieces the 1.25" barrel often houses a lower optical set and the field stop, depending where the optical design needs it to be.  Swapping the barrels in many eyepieces is not a simple business because of such things.

Edited August 27, 2021 by John

[Don Pensack]

44 minutes ago, johninderby said:

One of the newer type of click lock adaptors solves the undercut problem by using a nice wide clamping band. Similar wide bands used on some 2” diagonals now as well.

That's great, because the collet comes up all the way to the opening of the orange aluminum. It needs to grab the skinny little 1.25" section above the eyepiece's undercut to properly align the eyepiece

with the bore of the adapter, and on that one it does.  On this one, also, the internal collet comes up all the way to the opening:

https://www.cloudynights.com/topic/182290-new-redesigned-twist-lock-adapter-from-antares/

The Celestron one is very close, though:

https://agenaastro.com/celestron-2-to-1-25-twist-lock-eyepiece-adapter-93668.html

Some collet style adapters do not, so they can tip:

https://www.highpointscientific.com/baader-clicklock-2inch-to-1-25inch-adapter-t2-15b?utm_source=google&utm_medium=cse&utm_term=BAD-T2-15B&gclid=CjwKCAjwmqKJBhAWEiwAMvGt6AskBk8OqRTcxNGFBH7EoNEHB3a3oJr9vtaDY0obQwvjOTP1qLrtfxoCFi4QAvD_BwE

With that one, the fit depends solely on tolerances of fit of barrel through the opening.

[johninderby]

Another photo of the Celestron adaptor. Realised in the earlier photo hadn't screwed the orange part all the way down. 

Edited August 27, 2021 by johninderby

[Louis D]

2 hours ago, Don Pensack said:

Some collet style adapters do not, so they can tip:

https://www.highpointscientific.com/baader-clicklock-2inch-to-1-25inch-adapter-t2-15b?utm_source=google&utm_medium=cse&utm_term=BAD-T2-15B&gclid=CjwKCAjwmqKJBhAWEiwAMvGt6AskBk8OqRTcxNGFBH7EoNEHB3a3oJr9vtaDY0obQwvjOTP1qLrtfxoCFi4QAvD_BwE

With that one, the fit depends solely on tolerances of fit of barrel through the opening.

On top of possible tipping, one European user on SGL posted a video review where he complained that the Baader Clicklock pushes the barrel of whatever it's clamping to the side.

So, the BCL isn't even self-centering.

[Don Pensack]

No, it's not a collet, merely a mechanical way to press the brass split ring into the eyepiece.

[Tiago Ferreira]

I just wish that APM 2" fast lock (which until now was the best i could find in 2" centering precision) could became more popular so Markus could provide different measures for it. It became permanent on my focuser.

[jetstream]

22 hours ago, Louis D said:

On top of possible tipping, one European user on SGL posted a video review where he complained that the Baader Clicklock pushes the barrel of whatever it's clamping to the side.

How can we possibly do without Howies Paralizer? 😀

https://www.firstlightoptics.com/adapters/howie-glatter-parallizer.html

[Don Pensack]

Unfortunately, there are a lot of 1.25" eyepieces that don't work in the Parallizer adapter.

If the upper barrel protrudes sideways enough to stick out beyond the adapter, the eyepiece hits the thumbscrew,

which is angled up at a 45° angle.

There is at least one person here who machined off the top of the Parallizer to make it flat and installed his own thumbscrew 90° to the bore.

If the eyepiece does not hit the thumbscrew, though, there is no better adapter.

Edited August 28, 2021 by Don Pensack

[markse68]

21 minutes ago, Don Pensack said:

Unfortunately, thee are a lot of 1.25" eyepieces that don't work in the Parallizer adapter.

If the upper barrel protrudes sideways enough to stick out beyond the adapter, the eyepiece hits the thumbscrew,

which is angled up at a 45° angle.

There is at least one person here who machined off the top of the Parallizer to make it flat and installed his own thumbscrew 90° to the bore.

If the eyepiece does not hit the thumbscrew, though, there is no better adapter.

I picked one up recently and it’s a very nice clever device. I’m using it for collimation services with a Farpoint laser- it pretty much guarantees the laser is at least parallel (not necessarily central) to the optical axis of the focuser. It aligns itself to the 2” barrel with the same clever idea as it uses to clamp the 1.25”eyepiece. Ideal

Mark

[Don Pensack]

The amount the Parallizer is shoved sideways in the focuser matches the amount of sideways movement the other way by the thumbscrew in the Parallizer, so it is centered.

I wrote some illustrated instructions for the use of the Parallizer.

The Howie Glatter Parallizer.docx