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Eyepiece Undercut and Holder Brass Compression Ring

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#1 jkevn

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Posted 25 January 2021 - 05:12 PM

How do you know if your eyepiece barrel's undercut is compatible with your diagonal's brass compression ring? I want to avoid having the compression ring getting stuck in the undercut, or the compression ring getting warped!


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#2 scotsman328i

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Posted 25 January 2021 - 05:15 PM

How do you know if your eyepiece barrel's undercut is compatible with your diagonal's brass compression ring? I want to avoid having the compression ring getting stuck in the undercut, or the compression ring getting warped!

As far as I know, the undercuts on eyepieces and diagonal or focuser brass compression rings are universally machined to the same specifications to one another. Anyone else care to elaborate?



#3 SeattleScott

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Posted 25 January 2021 - 05:28 PM

You are more likely to have issues with a tapered undercut.

Scott
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#4 TOMDEY

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Posted 25 January 2021 - 05:39 PM

Yeah, that's one of our most common complaints here on CN. No standards whatsoever and eyepieces can indeed get hopelessly stuck in there... then, trying to extract it... you damage the focuser and drop the eyepiece on that premium gargantuan Primary Mirror. Why oh why did they ever improve smoothies by making them worse?!    Tom


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#5 scotsman328i

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Posted 25 January 2021 - 05:44 PM

Yeah, that's one of our most common complaints here on CN. No standards whatsoever and eyepieces can indeed get hopelessly stuck in there... then, trying to extract it... you damage the focuser and drop the eyepiece on that premium gargantuan Primary Mirror. Why oh why did they ever improve smoothies by making them worse?!    Tom

Interesting. I gather they don’t standardize the undercut process across the board. Good to know. 


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#6 SeattleScott

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Posted 25 January 2021 - 06:07 PM

Yeah, that's one of our most common complaints here on CN. No standards whatsoever and eyepieces can indeed get hopelessly stuck in there... then, trying to extract it... you damage the focuser and drop the eyepiece on that premium gargantuan Primary Mirror. Why oh why did they ever improve smoothies by making them worse?! Tom

Says the guy who mostly uses Dobs and doesn’t have to worry about the eyepiece pointing down after it finishes slewing to a target!

A teenager was looking through my scope when the diagonal came loose and flipped. Freaked the kid out. I was totally calm and relaxed because I knew there was a safety groove protecting the $300 eyepiece from plunging towards the asphalt below.

Scott
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#7 SeattleScott

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Posted 25 January 2021 - 06:13 PM

Interesting. I gather they don’t standardize the undercut process across the board. Good to know.

Ultimately kind of the point of the safety groove is to catch on the eyepiece. 99% of the time it is you pulling it out, not gravity, so catching is undesirable. But it can be a handy feature for the other 1% of the time. If you loosen the compression band enough and pull straight out, it shouldn’t catch much.

Scott
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#8 scotsman328i

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Posted 25 January 2021 - 06:16 PM

Ultimately kind of the point of the safety groove is to catch on the eyepiece. 99% of the time it is you pulling it out, not gravity, so catching is undesirable. But it can be a handy feature for the other 1% of the time. If you loosen the compression band enough and pull straight out, it shouldn’t catch much.

Scott

Scott, I personally have never even really thought about it as a problem. I’ve always chalked it up as the groove doing it’s job and saving my 26T5 from taking a southern vacation at terminal velocity out of the focuser. lol.gif


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#9 SeattleScott

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Posted 25 January 2021 - 07:27 PM

Scott, I personally have never even really thought about it as a problem. I’ve always chalked it up as the groove doing it’s job and saving my 26T5 from taking a southern vacation at terminal velocity out of the focuser. lol.gif

I’m with you. In the tech sector we would call this a “is it a bug or a feature “ debate.
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#10 scotsman328i

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Posted 25 January 2021 - 07:32 PM

I’m with you. In the tech sector we would call this a “is it a bug or a feature “ debate.

Bug or feature?...lol.gif



#11 Starman1

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Posted 25 January 2021 - 08:49 PM

As far as I know, the undercuts on eyepieces and diagonal or focuser brass compression rings are universally machined to the same specifications to one another. Anyone else care to elaborate?

Nope.

The brass split rings come in many widths and come in many distances from the opening.

The undercuts in the eyepieces vary in width and distances down from the shoulder.

THERE IS NO STANDARD OR REGULAR SIZE OR POSITION.

 

You can't even assume that an eyepiece and a star diagonal from the same company will mate up properly.

A TeleVue 24mm Panoptic in a TeleVue star diagonal gets tipped by the brass split ring hitting the upper lip of the undercut on the eyepiece, as just

one example.

 

So if the two mate up together perfectly, you have won the lottery.  The odds are NOT in your favor.


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#12 scotsman328i

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Posted 25 January 2021 - 09:01 PM

Nope.

The brass split rings come in many widths and come in many distances from the opening.

The undercuts in the eyepieces vary in width and distances down from the shoulder.

THERE IS NO STANDARD OR REGULAR SIZE OR POSITION.

 

You can't even assume that an eyepiece and a star diagonal from the same company will mate up properly.

A TeleVue 24mm Panoptic in a TeleVue star diagonal gets tipped by the brass split ring hitting the upper lip of the undercut on the eyepiece, as just

one example.

 

So if the two mate up together perfectly, you have won the lottery.  The odds are NOT in your favor.

Like I said, Don...as far as I know. Glad you elaborated on the topic.



#13 Starman1

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Posted 25 January 2021 - 09:05 PM

Ultimately kind of the point of the safety groove is to catch on the eyepiece. 99% of the time it is you pulling it out, not gravity, so catching is undesirable. But it can be a handy feature for the other 1% of the time. If you loosen the compression band enough and pull straight out, it shouldn’t catch much.

Scott

Aye, and there's the rub.

The eyepiece will start sliding easily out BEFORE the brass split ring has fully retracted into its groove.

So you don't learn the ring is still too tightened until the eyepiece is partway out.

The undercut on the eyepiece barrel can catch on the upper lip of the brass split ring groove.

It can also catch on the lip of the focuser.

On the way in, the bottom of the barrel can hit the lip on the bottom of the groove the brass split ring sits in.

And the top of the undercut on the eyepiece can hit the lip on the top edge of the focuser or diagonal.

And if the position of the brass split ring is a trace above the safety groove in the eyepiece (quite common), the eyepiece might come out anyway.

 

A standard for undercut width and position relative to the shoulder could be created, but that is unlikely.

 

Then there are the twist-lock and click-lock binders, which also do not mate properly with undercuts.

 

As I see it, brass split rings, twist locks, and click locks are all compatible with smooth eyepiece barrels.

And safety undercuts on eyepieces are compatible with thumbscrews pressing against the barrels.

But brass rings, twist-locks and click-locks are not compatible with safety undercut grooves in eyepiece barrels.

That last I'd call a Class C fit.


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#14 teashea

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Posted 25 January 2021 - 10:21 PM

The lack of standardization is unfortunate.  I don't have problems but it seems I certainly could.


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#15 luxo II

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Posted 26 January 2021 - 05:30 AM

How do you know if your eyepiece barrel's undercut is compatible with your diagonal's brass compression ring? I want to avoid having the compression ring getting stuck in the undercut, or the compression ring getting warped!

Look closely at the undercuts in your eyepiece barrels. If they have been machined with bevels - ie sloping edges, they shouldn't get stuck. The ones that get really badly stuck typically have sharp undercuts, without bevelled edges.

 

Of the ones I had with undercuts, I have sold all but one, and replaced with other eyepieces without undercuts. The grooved barrels adopted by Altair Astro are vastly superior to undercuts.

 

Some have long tapered undercuts (the SWA Q70 38mm is my last one). It's awkward in that its a sloppy fit in both compression rings and in rotolocks.


Edited by luxo II, 26 January 2021 - 05:32 AM.

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#16 Jon Isaacs

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Posted 26 January 2021 - 05:58 AM

The problem as I see it:

 

- Set screws work nicely with undercuts, they secure the eyepiece and do not hamper inserting or removing the eyepiece, they are pretty much universal because the setscrew is much narrower than the undercut.  You just have to make sure you loosen the them sufficiently.

 

- Somewhere along the way, people started to get bothered by the nicks in the barrels of their expensive eyepieces.  Thus the compression ring was born.   

 

- Some compression rings do not work well with some undercuts.  

 

- The simpler solution to the nick in the barrel problem is to use set screws that are softer than the eyepiece barrel.  Aluminum is a pretty good choice, Nylon is probably the best.  The only caveat with nylon setscrews is that they should be relatively large, at least 8-32 and preferably 10-32. 

 

My general approach is to remove the compression ring, put it somewhere for safe storage and replace it with a 10-32 Nylon thumbscrew.  

 

Works for me.

 

Jon


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#17 luxo II

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Posted 26 January 2021 - 06:31 AM

Not true, in 49 years of experience, with several focusers with compression rings - some with 1 set screw, some with 3.

As mentioned above there was never any standard adopted and imho this is a large part of the problem.

But as Altair UFF eyepieces have shown there is a much better solution - fine grooves milled into the barrel.

Edited by luxo II, 26 January 2021 - 06:37 AM.


#18 Jon Isaacs

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Posted 26 January 2021 - 06:37 AM

Setscrews work with some but not all eyepieces with undercuts - theyre ok with small light 1.25” eyepieces but not always ok with 2” ones - the Q70 I have is one that is a problem child.

What is going on there? What size thumbscrews are you using?  A 10-32 is approximately the same diameter as a 5mm.

 

I am using nylon thumbscrews with eyepieces like the 31mm Nagler and 21mm Ethos that weigh much more than the 38mm Q70s, I had a Q-70, have something very similar in the Svbony 34mm 72 degree, no problems so far.

 

Jon



#19 luxo II

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Posted 26 January 2021 - 06:42 AM

I sidestepped the whole problem.

My 2” focuser has 3 x 5mm nylon screws and a compression ring.

Into that I insert a van-slyke hex turret, which has a 2” female drawtube.

The turret holds 6 x 1.25 eyepieces, though it uses a nylon tipped oblique screw (at an angle) to fix each eyepiece very securely. This is really great, actually, best ever solution - better than both compression rings or the clicklock/rotolock as what van-slyke did is very compact.

I also have 3 x 2” diagonals - two with setscrews and one APM one with clicklock. The Q70 is a sloppy fit in all of them. Even in the focuser on the back of the scope with no diagonal. It has a hideous tapered undercut which is quite deep - to the extent nothing really grips it properly.

I now have a 30mm UFF (no undercut) so the Q70 is destined to become a paperweight. Or let my son pul it apart one day.

Edited by luxo II, 26 January 2021 - 07:18 AM.


#20 Jon Isaacs

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Posted 26 January 2021 - 08:25 AM

I also have 3 x 2” diagonals - two with setscrews and one APM one with clicklock. The Q70 is a sloppy fit in all of them. Even in the focuser on the back of the scope with no diagonal. It has a hideous tapered undercut which is quite deep - to the extent nothing really grips it properly.

 

 

I no longer have my 32 mm Q70 but I don't remember there being an issue. 

 

Does the q70 fully insert into the adapter so the top of the barrel is in the adapter?

 

Jon



#21 mikeDnight

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Posted 26 January 2021 - 09:16 AM

Undercuts are a marketing  ploy to make it look like you're getting something extra. They are hated by practically every serious observer, yet the companies who continue to force them on us, obviously think we're all thick and stupid, and can't be trusted to show adequate care of our precious eyepieces. They also continue to show contempt by refusing to alter the floored design. The better companies have listened and taken action, by introducing safety curfs, or mild shamfers. Others, better still, simply refused to add undercuts in the first place. 



#22 LDW47

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Posted 26 January 2021 - 09:58 AM

If many weren’t so careless and just kept a good firm grip on the ep until they knew it cleared the ring there wouldn’t be any accidents ! I specifically tried it quite a number of times after reading this same issue, in many similar threads about every couple of weeks. If it catches a bit a little jiggle lined it up so that it pulled out smoothly every time, many don’t have any patience, thats the big problem ! The stars aren’t going anywhere !


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#23 Gastrol

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Posted 26 January 2021 - 10:34 AM

As far as my 1.25” ep’s are concerned I fit 1.25” to 2” identical twist lock adapters to couple or three of them so I won’t run into that problem.



#24 Starman1

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Posted 26 January 2021 - 11:10 AM

As far as my 1.25” ep’s are concerned I fit 1.25” to 2” identical twist lock adapters to couple or three of them so I won’t run into that problem.

And some of the twist-lock adapters have smooth sides, too, without undercuts.



#25 Jon Isaacs

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Posted 26 January 2021 - 11:16 AM

Undercuts are a marketing  ploy to make it look like you're getting something extra. They are hated by practically every serious observer, yet the companies who continue to force them on us, obviously think we're all thick and stupid, and can't be trusted to show adequate care of our precious eyepieces. They also continue to show contempt by refusing to alter the floored design. The better companies have listened and taken action, by introducing safety curfs, or mild shamfers. Others, better still, simply refused to add undercuts in the first place. 

Please speak for yourself.  I see a great variety of experiences with undercuts.  Hate is a strong word..  

 

I consider myself a serious observer and the only issue I have with under cuts is using them in finder scopes without a focuser.  A smooth barrel is better for slip-slide focusing.  Otherwise, I have no problems with them. People seem to have trouble with them hanging up... That doesn't happen to me.  

 

Jon


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