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Hating brass compression rings...


ollypenrice
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I've always detested these things. No two makes are compatible so one person's EP or nosepiece won't sit squarely or securely in another person's focuser. Ha, but now I REALLY hate them; my Takahashi 2 inch adapter in a Takahashi holder (so all the same make) simply WOULD NOT come out because that idiotic bit of brass had become distorted. Heaving on it to try to pull it out I inadvertently gritted my teeth and, crunck, one of them (my teeth) broke and fell out. I now have a darned great gap where my endearing smile used to be. GRRR.

I had to use a hardwood drift to knock the adapter out, then I used some needle pliers to extract the damnable brass strip and hurl it in the general direction of Japan. Now that it is gone I can put the adapter in and out quite happily. It works perfectly.

I don't know about you but I look through the glass bits of an eyepiece, not at the chrome barrel to see if it has been marked by a lockscrew...

Olly

Edited by ollypenrice
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I too get cross with the compression rings in my varying diagonals. On more than one occasion the ring has moved and wedged itself in the safety recess of an eyepiece. To date the worst combination is a Williams 2" diagonal and my TV 17mm Nagler.

That said I have not had to plan a trip to the dentist as a result. I whinced when i read your post, sorry to hear about your teeth, that really is suffering for your art!

Adrian

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Yeah, I feel your pain ... I get the general impression that Televue's eyepiece groove is in a different place to everyone else's. Now, if there was a narrow groove running lengthwise down the barrel, instead of round it, it would prevent the "piston effect" that causes difficulty when the fit is too good ....

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I have had a few diagonals that were absolute pigs and really knew how to put up a fight when removing an eyepiece. The older Televue eyepieces caused the most problems with their really sharply cut safety groves.

Funnily enough since I replaced the two diagonals that I use with Astro-Physics diagonals nothing seems to hang up any more. :)

John

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Sorry to hear about the dentistry Olly.

I have on a few occassions had a Televue eyepice get caught because of the barrel design. Thankfully I have never had to resort to knocking one out with a lump of wood though....

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I'm with you Olly (although my teeth are still all intact :))

What on earth is so hard about putting 3 locking screws 120 degrees apart....a good tight fit with no flexure....I hate compression rings too!

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I've seen some adapters and eyepieces with square undercuts with sharp corners.

These designs are badly thought out in my opinion. The undercut should blend out smoothly to the nominal diameter over a mm or so.

Rob if you hate them (compression rings) that much then you might have just swayed a design decision I have been in a dilemna over for months!

Edited by wayne weedon
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I on the other hand happen to really like them. The baader one is really chunky for use in the dark. I have had problems with the blinkin' Williams Optics diagonal due to its large conical undercut medaning I can;t clamp properly on it. In this case neither a screw or a clamp give repeatable centring. The other option is the quick-lock clamp from Baader. I have the 1.25" one. That is excellent for clamping, cetring and release but its too easy to turn the wrong way in the dark and release the eyepiece onto the floor.

Swings and roundabouts I reckon. Sorry about the tooth.

Mike

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I like brass compression rings because they prevent marring of eyepiece barrels. They can hook on eyepiece undercuts, but the problem is excessive undercuts with square edges, not the brass compression ring itself.

Vixen eyepieces have a perfectly adequate undercut of 0.13mm and they do not hook up, unlike the HR Planetary where the undercut is 5 times as deep - an unnecessary 0.65mm! The grooves are also of different lengths, but that is less on an issue.

I have also had a 2" adaptor that was an interference fit which would lock solid in the barrel at the slightest opportunity. Some agreed published standards would be good, but this seems unlikely in an industry that does not even publish basic data about its products...

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Twist lock is the way to go. We have them for 1.25" EP's but could do with them as standard on 2" or at least as an option!!

Here, here !!

I have a Tak 1.25" diagonal with twist lock. Quite wonderfull.

Andy.

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Nothing new under the sun, I have twist locks on my 70s Towa and 1964 swift. Much nicer.

I modded bot my 127 EDT and 102 ED with triple clamp screws ala moonlite, safer and easier.

Philj

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<<How nice not to be alone! ROb's 120 degree idea is the answer.>>

I second that, although any kind of push-fit and clamping system does seem to have a fundamental weak point: two sliding tubes can't be in perfect contact and even when clamped in three places can have the potential for some wobble. (Think of the additional contact points required to keep a Crayford focuser stable.) Two sets of three clamp screws would be nice!

Remember a time long ago when all eyepieces etc. were attached via a standard RAS thread? Old-fashioned and inconvenient, but there's a lot to be said for solid threaded couplings and attachments throughout, imo.

Adrian

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Remember a time long ago when all eyepieces etc. were attached via a standard RAS thread?
Yes ... a right pain they were too, fortunately those heavy brass eyepieces tended to crack the paving stones rather than break when you dropped them.

When I had a Frank 6" F/8 Newt - with the rotating low profile helical focuser, RAS threaded - for medium & higher powers I used 24.5mm push in EPs (Swift, quite reasonable really) in an adapter which had three sprung "fingers" which held the EP quite securely & without significant sideways wobble (unless you pushed very hard) yet allowed easy changes. Simple, really.

The issue with "standard" 1.25" & 2" push-fit fittings these days is that different brands seem to be using different standards; quite apart from those horrid retaining grooves, some are a very snug fit - almost an interference fit - & if a filter is fitted there is a significant chance of sucking its glass out of its mount when removing the EP from the adapter. Others are horrible sloppy - usually the worst offenders are collimation tools which really need to be accurate ....

Engineers of the world (especially China), please decide on the diameter of the fitting & machine the parts so that the barrel diameter is exactly 2 thou less than that of the hole it goes into. If you must have a retaining groove, make it shallow and make the sides tapered at a shallow angle, not a sharp right angle. And decide on a standard groove width and depth relative to the mating face. Thanks in anticipation (but not expecting much!)

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<<fortunately those heavy brass eyepieces tended to crack the paving stones rather than break when you dropped them.>>

Agreed, you didn't want to stick your foot out to save one of those on the way down!

<<Engineers of the world (especially China), please decide ...>>

Hm, if only.

Adrian

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Some try to think about the undercuts :)

The adapters I make for FLO have an undercut as per the drawing extract below. Tapered and blended with rads both ends and shallower taper at the nose end to assist extraction.

The biggest problem is trying to deal with some pretty sloppy tolerancing on a.n.other manufacturers kit. The tendancy is to HAVE to err on the looser side because oneday someone is going to have an issue with parts not fitting. I can hold a couple thou all day no problem, some others could not care less (Includes some well known apparently high end brands that some rave about). So sometimes it seems a lose lose situation.

Wayne....

flo_undercut.jpg

Edited by wayne weedon
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After fitting an 2" extension plus a Canon adaptor into my ED80, I noticed a dreadfull droop :) in the assembly. So I drilled and taped a new thread into my highly polished anodised ED80 at 120deg to the existing clamp screw, then did the same to the 2" extension. The assembly is now quite firm :( with none of the wobble. Regarding the compresion ring, I can see the problem and hope it does not happen on my outfit.

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Just to note that if you really do not like it, a brass compression ring can be easily removed. You rotate the ring so one end is close to a thumb screw. Screw this in to push the end of the ring clear of the grove. The ring can then be simply hooked out with your finger.

To restore the non-marring properties all you then need to do, is to source nylon tipped thumb screws of the right thread and length. Good luck...

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I'm with you Olly (although my teeth are still all intact :))

What on earth is so hard about putting 3 locking screws 120 degrees apart....a good tight fit with no flexure....I hate compression rings too!

My WO reducer, SXVF-H16 and SX filter wheel are all entrusted to the integrity of a single nut compression ring. It bothers me a lot!

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