Eyepieces and eyepiece holders

dunc66 · #1 07-12-2009, 07:48 AM

Hi

a couple of simple questions.

Are eyepieces always inserted onto the holder (focuser, barlow etc) as far as they will go? Sounds like a dumb question, but I have an Ultrascopic which has the "locking groove" located towards the bottom of the eyepiece tube. So, for this to engage with the locking screws on the holder, it is not fully inserted.

The other question is to do with the eyepiece holder. Are they designed to carry the eyepiece resting on the bottom with the locking screws at 10 and 2 o'clock or at 9 and 12 o'clock, or it doesn't matter?
Thanks

erick (Eric) · #2 07-12-2009, 08:52 AM

Hi.

Yes eyepieces are designed to be inserted fully so the eyepiece body sits on the top of the focuser - so hopefully the eyepiece is: 1) nice and square, and 2) securely held.

However, everyone has found a situation where an eyepiece may not be inserted fully. 1) 'cause it just won't go in fully - sometimes this happens with various extension tubes, adapters etc. 2) 'cause to do so would damage a filter. I know of 1.25" eyepieces whose barrels are long enough so it would hit a 2" filter in a 2"--> 1.25" adapter. 3) 'cause you just have to to achieve focus - lifting an eyepiece out some distance is sometimes required.

I don't believe the orientation of the locking screw(s) matters - not to any significant degree for observing. But, being consistent is a good idea. I always have mine in the same place, but that is so I can change eyepieces by touch only in the dark - I always know where to find the locking screws.

dunc66 · #3 08-12-2009, 07:19 AM

Hi eric, thanks for the reply.

I have an Ultrascopic 7.5 and a 15mm 1.25" eyepiece. The distance from the eyepiece collar to the retaining screw groove on the barrel is very different between them, maybe 10-15mm. Why is this so ?

With regard to the screw up/down question. If the screws are at the top of the eyepiece holder then the weight of a heavy eyepice would act to pivot the lens barrel about the screws as allowed by the looseness of the fit. I was thinking that if the screws were at the bottom, then any pivoting force would only serve to push the eyepiece more firmly to the roof of the eyepiece holder. Not sure if this a significant worry, but given the amount of time it can take to collimate a reflector ........

Cheers

erick (Eric) · #4 08-12-2009, 10:35 AM

"Why is this so?" - I don't know. I wish all eyepieces had smooth barrels and none had the "safety undercut". I don't think there is a standard for the distance from the top of the focusser where the eyepiece sits, to the clamp device, be it a compression ring or set screw(s)

I'd always prefer the compression ring style of holder to one with one or two set screws.

Perfect is a self-centring adapter (SCA) as used in the Hotech laser collimator and their superb camera mounting tube. Search out threads on the Hotech collimator here and on Cloudy Nights and read pages of arguments about eyepieces and set screws - eg. why bother collimating with a SCA collimator when the eyepiece is going to be pushed to one side by the set screw anyway. See also thoughts on Hotech's website.

erick (Eric) · #5 08-12-2009, 10:36 AM

A thought - is one barrel screwed on upside down on one eyepiece? Sometimes they are threaded all the way with the "filter thread" so they could be inverted and would fit?

CoombellKid · #6 08-12-2009, 02:14 PM

My advice is forget about the locking groove on all EP's and try and
follow Eric's 1 and 2 rules where you can. There too many manufacturers
that have their own idea about the locking groove. I have a
Feathertouch focuser, U/O HD's, Pentax XW's and Nagler t5's and none
of them fit the locking groove... I dont think you can get much more top
of the line than the list I just mentioned, still no uniformity with the
locking groove.

On the other hand.... it would be interesting to know if Meade or TV
telescopes and their respective EP locking grooves lined up with the
focuser locking rings. Anyone with such setups care to enlighten us?

Cheers,CS

dunc66 · #7 13-12-2009, 06:43 AM

Well I think this thread can go in the bin. Eric is correct. The lens barrel was screwed on upside down. Both eyepices the same now and both grooves interact with the focuser locking screws. Nice!

Cheers.

space oddity · #8 13-12-2009, 07:52 AM

Eyepieces do not always have to go right in. Proof-parfocalising rings are freely available, proving there is some latitude in eyepiece positioning.

erick (Eric) · #9 13-12-2009, 09:29 AM

Gee, I'm right for once

Kevnool (Kev) · #10 13-12-2009, 02:47 PM

Quote:

Originally Posted by erick

Gee, I'm right for once

Legend Eric.
Cheers Kev.