Plossl that stopped focusing

[MrShorty]

Last observing session, I discovered that my Meade Super Plossl 12.4 will no longer focus right. I'm fairly confident that it is in the eyepiece and not the telescopes because every other eyepiece I have focuses nicely in both telescopes. Stars in this one will appear as "horizontal" lines on one side of focus. At "focus" will be circular blobs. Then "vertical" lines on the other side of focus.

Just looking at the eyepiece, I cannot see anything obvious (like a crack or a smudge or dirt). I have never had trouble with any of my eyepieces before. This one was quickly on the road to become one of my favorites in my collection, so I'm hoping there is something I could do to fix it, but have no idea what to look for.

[sdbodin]

Sounds like astigmatism, one lens must have come loose and got at an angle inside the eyepiece. Disassembly is the only solution. But be sure to keep all the lenses in the correct order and correct side up.

my guess,
Steve

[Lady Fraktor]

I would agree, it sounds like something has come lose.

[MrShorty]

If I disassemble the eyepiece, it would be my first time disassembling an eyepiece. Before I start dismantling, does anyone have a rough description of what will come out? A schematic of typical Plossl construction? Tips for handling things so they stay clean without damaging coatings?

[Ruud]

I'd put the eyepiece on the table, eye lens down. Then unscrew the 1.25" section just a little, tap a bit against the side so that everything gets a chance to settle, and then tighten the 1.25" section. I think that might solve the problem.

[notFritzArgelander]

I'd put the eyepiece on the table, eye lens down. Then unscrew the 1.25" section just a little, tap a bit against the side so that everything gets a chance to settle, and then tighten the 1.25" section. I think that might solve the problem.

A good trick to try short of complete disassembly. Do this first.

[John Baars]

Note that not all eyepieces are made the same way. Loosening the 1.25"barrel may not be enough. Sometimes the lens system is held in place by a second ring. Look at this picture:

The yellow arrow points at the 1,25"barrel thread. The red arrow points at the ring that hold the lens system in place. In this eyepiece the ring with the red arrow should be loosened a little bit before executing the operation as described above. Those retaining rings can differ in size from one or another eyepiece.

002IMGP4631 - kopie.JPG (62.24 KiB) Viewed 3278 times

[MrShorty]

All my eyepieces have the "center" retaining ring. Have tried loosening and tapping. Now need to wait until I get home to the telescope and can give it a try.

[MrShorty]

Tested by pointing at the trees on top of the mountain, and it seemed to focus just fine. Hopefully the clouds will part enough to pick out a star to test on.

If all tests okay, how tight should the retaining ring/nut be? It was obviously loose when I first poked at it. Should it be snug, or should there be some slack?

[sdbodin]

Tested by pointing at the trees on top of the mountain, and it seemed to focus just fine. Hopefully the clouds will part enough to pick out a star to test on.

If all tests okay, how tight should the retaining ring/nut be? It was obviously loose when I first poked at it. Should it be snug, or should there be some slack?

Sounds good. I would tighten just snug, so there are no rattles, but not tight.

Steve

[notFritzArgelander]

Tested by pointing at the trees on top of the mountain, and it seemed to focus just fine. Hopefully the clouds will part enough to pick out a star to test on.

If all tests okay, how tight should the retaining ring/nut be? It was obviously loose when I first poked at it. Should it be snug, or should there be some slack?

Think "finger tight". No slack but don't clamp down on it.

[MrShorty]

Well, the clouds were thin enough for Jupiter, Saturn, and bright stars to penetrate, so I managed to test it, and it seems just fine. For now, we will consider this resolved.

[notFritzArgelander]

Well, the clouds were thin enough for Jupiter, Saturn, and bright stars to penetrate, so I managed to test it, and it seems just fine. For now, we will consider this resolved.

Good to hear!

[Michael131313]

I am always impressed by the amount of information and the helpfulness of the forum members. Thank you all.

[MrShorty]

I am always impressed by the amount of information and the helpfulness of the forum members. Thank you all.

Amen!

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