32 replies to this topic

[Isaac M.]

I just got a cave astrola 8 deluxe from a fellow club member and I am having trouble securing some of the eyepieces in place. I believe it is the original focuser. I found that by twisting it tightens. But some eyepieces are too big or two small even though they are all 1.25. I hope that make sense. If you need photos I can provide them.

 

 Thanks in advance,

Isaac

[deSitter]

I just got a cave astrola 8 deluxe from a fellow club member and I am having trouble securing some of the eyepieces in place. I believe it is the original focuser. I found that by twisting it tightens. But some eyepieces are too big or two small even though they are all 1.25. I hope that make sense. If you need photos I can provide them.

 

 Thanks in advance,

Isaac

Sounds like a barrel is stuck in the focuser.

 

-drl

[Isaac M.]

Now that I looked more closely it appears that that could be the case I will try to get it out. 
 

Thank you!

[Isaac M.]

It was a four inch long black tube, I think it may have been for the focuser. It didn’t make things any better.

 

[deSitter]

It was a four inch long black tube, I think it may have been for the focuser. It didn’t make things any better.

That is probably the drawtube. Post some pics.

 

-drl

[Isaac M.]

Here are some pics 

Attached Thumbnails

• 
• 
• 
• 

[cbogard]

Both the focuser tube and the eyepiece barrels of my mid-50s 6” f8 Newtonian were made slightly flattened into an elliptical shape so they can be inserted easily, then rotated to lock them in place.  More modern EPs are usually loose, and will drop out if the scope tube is rotated into the wrong position.  I’ve considered trying a strip of thin tape on the newer EP barrels, but, having other scopes, haven’t bothered.  
 

Charles

[Isaac M.]

It’s really loose in the others, not just might fall but will fall if I let go.

[deSitter]

The part with the cut slots goes on the outside. I would clean out the interior of the focuser tube, which seems to have some oxidation/corrosion that is hampering the drawtube. The slotted area is meant to grip the eyepiece by friction. You can increase its effectiveness by bending in the "wings" a little bit.

 

The drawtube should go into the focuser firmly but not excessively so. It is used for rough focus. One setting should work for most eyepieces. The slots should never be covered.

 

-drl

[davidmcgo]

If the black tube inner diameter is 1.25” all you can do is bend in the tabs along the slot a bit to add more friction.  Not sure what holds that into the focuser, all the ones like that I have seen had a thumb screw in the knurled collar somewhere.

 

When this was made there were not any eyepieces with undercuts, tapered barrels, or weighing more than a few ounces so it will be a challenge with a lot of modern stuff.

Dave

[Isaac M.]

I will try then give an update, thanks!

[Isaac M.]

Even bending a bit doesn’t help much at all. There is still a big gap between the eyepiece and the draw tube. 

[Isaac M.]

[Isaac M.]

After more bending it at least stays, but not very well. I just don’t want to bend it to much that it snaps. 

[deSitter]

After more bending it at least stays, but not very well. I just don’t want to bend it to much that it snaps. 

You couldn't if you tried have at it.

 

-drl

[jimr2]

Hi, this won't help you any with the problems you're having with your old Cave Astrola focuser, but depending on the vintage of your Cave, that focuser may not be OEM. I have a 1973-74 Astrola delux 8", f/8 I bought new, and it's 1-1/4" focuser is not like yours at all. Mine has a square (or rectangular) base, not round like yours, and has black plastic focusing knobs, rather than metal ones like yours. And I'm pretty sure it has a single thumbscrew in the top end of it to secure the eyepieces into it (I can't get at the scope right now very easily...). Again, I don't know the vintage of your scope, but I guess if it is much older than the early 70's, then it's quite possible yours came with a different type of focuser.

 

Anyhow, good luck, and many happy views through your classic Cave!

 

-jim-

[deSitter]

Hi, this won't help you any with the problems you're having with your old Cave Astrola focuser, but depending on the vintage of your Cave, that focuser may not be OEM. I have a 1973-74 Astrola delux 8", f/8 I bought new, and it's 1-1/4" focuser is not like yours at all. Mine has a square (or rectangular) base, not round like yours, and has black plastic focusing knobs, rather than metal ones like yours. And I'm pretty sure it has a single thumbscrew in the top end of it to secure the eyepieces into it (I can't get at the scope right now very easily...). Again, I don't know the vintage of your scope, but I guess if it is much older than the early 70's, then it's quite possible yours came with a different type of focuser.

 

Anyhow, good luck, and many happy views through your classic Cave!

 

-jim-

That looks like the Sky Micro and yes IIRC it was part of the 8" Deluxe package. The Sky Micro Giant was on the 10" and larger. OP, note that this focuser also has a helical aspect.

 

-drl

[Isaac M.]

The owner couldn’t remember exactly which year it was and the mirror only said cave optics, no date or anything else that I could see. He did say it was from sometime in the 60s though, so an older model for sure. This is what it looks like, any idea what it’s worth assuming its mirror is in good condition? I have no intentions of selling, but am curious. 

[PiSigma]

The paint scheme and OTA nameplate say it is 1972 or later.

[davidmcgo]

You could get a small stainless hose clamp to go around the drawtube and compress the slots that way.  
 

Dave

[jgraham]

I have this same exact focuser on a vintage 6” f/20 Classical Cassegrain. That sleeve that you pulled out is supposed to be press-fit into the focuser draw tube so that the slit end is flush with the inside bevel. When it’s installed properly it blends in smoothly with the inside of the draw tube making it hard to see. The split end forms a spring to apply a slip fit to 1.25” eyepieces. Soooo, I would clean the inside of the draw tube and the outside of the sleeve. While the sleeve is out, give the spring section a bit of a squeeze to encourage it in a bit, then press the sleeve back into the draw tube with the slit section about 2mm inside the end of the draw tube. It sounds like yours might have gotten caught on an eyepiece and shoved too far in to engage any eyepieces afterwards, so you lost the friction fit element.

[Isaac M.]

Thanks for all the helpful information everyone!

[jgraham]

I grabbed a quick pic...

 

 

Enjoy!

 

[Isaac M.]

Definitely looks very similar, thanks!

[jragsdale]

Had a similar thing with an Edmund focuser on a 3" f/15 refractor. Too loose, a diagonal with a heavy eyepiece would flip upside down if it was the slightest off-centered. Ended up 3D printing a small ring with a small #10-24 screw and thumb nut to add some tension. Marginally more attractive than a pipe strap.

Attached Thumbnails

•