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Eyepiece Safety Undercuts - a Bad Idea From the Start

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#26 39.1N84.5W

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Posted 19 July 2019 - 11:53 PM

For the binoviewer crowd and compression rings... I prefer smoothies. Just bought a new pair of Kokusai 9mm orthos. Smooth! Baader Genuine Orthos are also smooth.
Hopefully more manufacturers will go this route.
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#27 SteveG

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Posted 20 July 2019 - 01:25 AM

I ran a poll on this popular topic about 9-10 years ago. A lot of people voted (I think about 300). As I recall, about 33% were in favor of undercuts, to about 66% against. There was also a tapered category, but that eventually morphed into the undercut category.


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#28 Jon Isaacs

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Posted 20 July 2019 - 06:56 AM

So far, no jammed compression rings here. Keeping my dedos cruzados. smile.gif

This is a situation particular to the Paracorr II and the TeleVue barrel extensions.  

 

Jon


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#29 TOMDEY

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Posted 20 July 2019 - 08:49 AM

The one CAUTION in all this --- some manufacturer will duly note our concerns and come up with a solution that is a combination of these >>>

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  • 250 improved next generation focuser.jpg

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#30 Cotts

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Posted 20 July 2019 - 09:08 AM

Mark me as 100% against undercuts.  I often observe with a Discmount DM6 which 'locks' on a target by friction, not clamping.

 

I've lost count of the times that I change eyepieces only for the undercut to catch as I pull it out and the scope moves and I lose my target.  This is NOT the fault of the wonderful DM6 mount - it simply was not designed to survive a small tug and stay on target..

 

Hello, entrepreneurs and machine-shoppers.  There is a large market out there waiting for after-market smooth eyepiece barrels. Screw the old one off, screw in the new one.....

 

Even better.  Starlight Instruments!!  <Tap,tap,tap Hey, Jon!!!! >  Come up with a way to replace an undercut 2" barrel with a PARALLIZER barrel.  Imagine - no hang-up, and your eyepiece is perfectly square in the holder....  Would some people pay $75 to put one of these on expensive eyepieces?   

 

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#31 Asbytec

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Posted 20 July 2019 - 10:13 AM

Duly noted... :lol:



#32 John Fitzgerald

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Posted 20 July 2019 - 10:25 AM

The more expensive eyepieces have lenses in the lower barrels.  They cannot be screwed off and replaced like an old orthoscopic.  Also, pulling them out using a parfocal ring may not leave enough "in travel" to focus on some scopes, especially reflectors.  There is not an easy, permanent solution for the market.  Any aftermarket device will have to be brand and type specific.  Some use tapers, some use undercuts, and there appears to be no standardization.


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#33 markb

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Posted 20 July 2019 - 10:31 AM

After additional thought (recall speed has lengthened as the brain has gotten more stuffed and slower with age), I believe one impetus for the original 'safety' (not that it worked out that way for moderrnusers) undercuts was the proliferation of giant, heavy and EXPENSIVE ultrawide (for 1980) eyepieces. Not to point a finger at Nagler 13s, but... 1.5 pounds of 'glass in a beer can' makes a scary explosion when it falls from a scope; I sold mine right after it arrived. Should have kept it of course, these are collector items now. I only kept my 4.8 and 7mm Nagler originals, ad still love them. I observed on grass, but still cringed when an eyepiece worked free and slipped out on a scope movement. I suspect a N13I or one of the new 100 degree eps would fare well even on grass.

 

When eps went from $50 to $300, nearly as much as a everyday scope, BEFORE the advent of compression rings, safety cuts were a really good idea. But ep makers failed to drop them when compression rings became common. If the scope came with compression ring backs they might have.

 

The Paracorr issue is new to me, something to be aware of with older eps.

 

Replacing barrels would be nice, but, even without the lenses referenced by John, pitch and thread diameters vary widely in something as seemingly simple as an ep barrel. I tried for years to replace a missing barrel on an ep, and ended up having to post a want ad for a damaged ep.

 

While trying out barrel swaps, I think I hit at least 8 different diameter and thread combinations, plus the threaded inside or outside choice.

 

I will note that most of the chinese stuff seems to use a common thread pitch and diameter, and even that I cwould not count on. It may offer hope to GSO barrel swappers though.


Edited by markb, 20 July 2019 - 10:36 AM.


#34 Rustler46

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Posted 20 July 2019 - 10:40 AM

One thing to keep in mind when considering barrel swaps is the field stop on many eyepieces is located within the lower barrel. This would need to be supplied with any non-undercut barrel.



#35 TOMDEY

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Posted 20 July 2019 - 10:59 AM

The more expensive eyepieces have lenses in the lower barrels.  They cannot be screwed off and replaced like an old orthoscopic.  Also, pulling them out using a parfocal ring may not leave enough "in travel" to focus on some scopes, especially reflectors.  There is not an easy, permanent solution for the market.  Any aftermarket device will have to be brand and type specific.  Some use tapers, some use undercuts, and there appears to be no standardization.

Yes, indeed! Because of the lack of standardization, the focuser guys need to make the in-hole fat enough to accept any and all eyepieces... and the eyepiece guys need to make the barrel skinny enough to slip into any and all focusers... which results in, on average, a lot of slop to begin with. Then throw in undercuts, tapers, faux compression rings, different anticipatory longitudinal locations... any your left with the mess that we have now. I do note that (as others have mentioned)... virtually all of those fake compression rings are nothing more than maliable brass with a set-screw behind it... which is not a compression ring, at all... just cheap, disfunctional look-alike.

 

[A true compression-ring tightens like a belt, squeezing the entire barrel (of the eyepiece) uniformly. Most-ideally, it maintains axial centration while achieving that function.]    Tom


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#36 John Fitzgerald

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Posted 20 July 2019 - 11:05 AM

<snip>

[A true compression-ring tightens like a belt, squeezing the entire barrel (of the eyepiece) uniformly. Most-ideally, it maintains axial centration while achieving that function.]    Tom

Yes, a true compression ring should work like a collet.


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#37 TOMDEY

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Posted 20 July 2019 - 11:05 AM

Well... I'll be dipped... I just looked at my two (high-end) focusers and... they don't use actual, genuine, compression rings. But at least, in their favor, they comprise two or three thumb-screws around the periphery... which is way better than the old-fashioned one only.

 

And I still hate undercuts...    Tom


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#38 Shorty Barlow

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Posted 20 July 2019 - 12:14 PM

There are false compression rings?!! shocked.gif

 

gallery_249298_10284_47243.jpg

 

These are after market visual back compression rings for my 72mm and 80mm Evostars.

 

gallery_249298_10284_314603.jpg

 

They certainly make rotating the diagonal easier.


Edited by Shorty Barlow, 20 July 2019 - 12:38 PM.


#39 Starman1

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Posted 20 July 2019 - 12:38 PM

The best system for any eyepiece that has an undercut, whether cylindrical or conical taper, is 2 thumbscrews pressing on the barrel.

One screw still allows a wiggle.  Two screws remove the wiggle and guarantee repeatable registration.  Three screws are bad because the 3rd screw presses the barrel away from the registered contact with the focuser drawtube.

 

A brass split ring (it doesn't actually compress around the barrel--the brass ring merely provides a brass interface between screw and barrel) will work fine IF and only if the ring corresponds perfectly to the undercut on the eyepiece barrel.

And if the eyepiece undercut is the conical taper, a brass ring can distort and twist and stay that way.  ES gets around that by using a stronger, stainless steel, ring, but it requires more force to tighten against the eyepiece, and a larger movement of the screw.

 

Collet style binders, like the twist lock systems or the Baader Click lock are good systems, but don't always mate up correctly with undercuts on barrels (in fact, they almost never do), and the undercuts also reduce contact with the collets.

And, 2" collets are as rare as hen's teeth, so we're primarily talking 1.25" here.

 

So the way I look at it, undercuts on barrels are good if the thumbscrews press directly on the barrel.

And brass split rings and collets are both good on smooth barrels.

They're just not designed to work well with each other.

 

People have, for some reason, become paranoid about leaving marks on the barrels with thumbscrews.  The obvious answer to that is large diameter nylon or nylon-tipped screws.

They even work well on smooth barrels.

 

So the reason for the brass split ring binding is.........?

 

I used a copper tape to fill in the undercuts in the barrels of my eyepieces, and I'm amazed at how much easier they go in and out of the focuser/Paracorr/star diagonal/Barlow.

I hate undercuts, and that is how I feel about it.  My Paracorr has a smooth barrel, and it's so easy to remove and install in the focuser.  I remember when all eyepieces were that easy.


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#40 Ihtegla Sar

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Posted 20 July 2019 - 01:08 PM

Add my vote to the HATE undercuts and tapers crowd. I find them frustrating and annoying because the eyepieces are ALWAYS snagging when I am trying to remove them. I've dropped and nearly lost several thumb screws trying to deal with these annoying contraptions. I would rather risk dropping an eyepiece than having to deal with the constant annoyance. I may have to look into taping them.

Edited by Ihtegla Sar, 20 July 2019 - 01:23 PM.

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#41 Scott99

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Posted 20 July 2019 - 01:23 PM

I'm not stuck with anything for a generation!  lol.gif   I'm currently holding 27 eyepieces and 23 of them have smooth barrels.  Plus 2 Barlows....also smooth barrel.  Most of the time I run completely free of annoying snags on my diagonal.

 

Vote with your feet....vote with your dollars, there's always another option.


Edited by Scott99, 20 July 2019 - 01:24 PM.

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#42 Starman1

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Posted 20 July 2019 - 01:51 PM

Even some current eyepieces, like Vixen SLV or APM UFF or Baader Morpheus, or.........



#43 John Fitzgerald

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Posted 20 July 2019 - 02:26 PM

The people who have some control over manufacturing that I have talked to in various venues over the past few years seem very resistant to abandoning the undercuts.  Not naming names....



#44 John Fitzgerald

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Posted 20 July 2019 - 02:32 PM

<snip>

I used a copper tape to fill in the undercuts in the barrels of my eyepieces, and I'm amazed at how much easier they go in and out of the focuser/Paracorr/star diagonal/Barlow.

I hate undercuts, and that is how I feel about it.  My Paracorr has a smooth barrel, and it's so easy to remove and install in the focuser.  I remember when all eyepieces were that easy.

Don,

Do you use the 5mm wide copper tape that is widely available, and is adhesive backed?   How long does it stay on the eyepiece?  Does the adhesive make a mess?  Is there a particular technique you use to apply it?



#45 Starman1

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Posted 20 July 2019 - 02:41 PM

I used a thin copper tape 8mm wide (they say 3/8", but it's a tad narrower) and it was thin enough that it took 2 or 3 windings to build it up to the same depth as the undercuts.

No noticeable glue and the tape does compress under a thumbscrew, but not noticeably under a brass split ring.

https://www.amazon.c...e?ie=UTF8&psc=1

 

it may be available for less, or in smaller length (recommended).


Edited by Starman1, 20 July 2019 - 02:42 PM.

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#46 markb

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Posted 20 July 2019 - 02:48 PM

Thanks for the tip Don.

 

Since I discovered UHMW tape that was available in controlled thicknesses I had figure I would try it if needed, but worried about it being too soft. Copper tape should resolve that issue, and thickness specs were listed. Saved in my 'for later' cart!



#47 TOMDEY

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Posted 20 July 2019 - 03:07 PM

Thanx to Don for that very concise summary of issues and solutions! I also find that two beefy nylon thumbscrews about 120o apart are secure, convenient, repeatable and simple! I've even amended that to holders that were otherwise deficient. The drill press, tap, and screws from the hardware store... problem solved. And Don's mention of Copper Tape... sounds nice and would even look good! We had aluminum tape at work in various thicknesses --- think I have some out in the shop. And metalized Mylar tape. With a little care on a rainy day... I could do my eyepieces and be done with bemoaning the undercuts.

 

Almost makes the idea of an "undercut correction kit" attractive.

 

I wonder if any eyepiece manufacturers are listening?! --- Bet their conclusion would be that the general mass-market needs undercuts to reduce returned dropped eyepieces. Returned with no explanation, other than claiming it's "defective" --- when it obviously has been dropped onto the concrete sidewalk!

 

[I recall the time we returned an Interferometer to Zygo... that one of the engineers had dropped onto the High-Bay concrete floor! Of course we fessed up to that. Zygo did not suddenly add undercuts to the interferometer!    Tom



#48 Scott99

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Posted 20 July 2019 - 03:45 PM

I don't have all of these anymore, but this is typical of what I use, this random photo from my computer has 21 eyepeices from 4mm to 45mm, a barlow and star diagonal and no undercuts in the lot:

 

minglass.jpg


Edited by Scott99, 20 July 2019 - 03:46 PM.


#49 25585

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Posted 20 July 2019 - 03:47 PM

Vixen HR do not....



#50 John Fitzgerald

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Posted 20 July 2019 - 04:25 PM

<snip>

 

I wonder if any eyepiece manufacturers are listening?! --- Bet their conclusion would be that the general mass-market needs undercuts to reduce returned dropped eyepieces. Returned with no explanation, other than claiming it's "defective" --- when it obviously has been dropped onto the concrete sidewalk!

Tom,

You are exactly right.  The general mass market (not the CN market) probably demands it.   That's what some of the people who control mfg tell me.


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