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Edmund Scientific Telescope help

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36 replies to this topic

#26 ccwemyss

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Posted 07 January 2021 - 08:30 PM

So Robert, if the cell is front loading, then Druchti's missing the retaining ring. Do you have advice for a replacement or substitute?

 

Chip W. 


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#27 clamchip

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Posted 07 January 2021 - 09:03 PM

One possibility is to go to a hobby shop and buy a length of music wire.

It comes in 3 ft lengths if I remember correctly.

Fashion a ring from this springy steel wire a little larger than the inside

of the cell.

When you hold the lens with your cotton covered finger tips, go ahead

and invert the telescope so the tube is pointing zenith.

Now take your springy music wire ring and push it into the cell to hold

the lens in place.

Another idea is take the cell to a machine shop and they can make

retainer ring, whatever the cost this telescope is worth it.

 

Something we are forgetting, does the lens fit the cell?

I'm wondering why it's apart, if the original lens was damaged and a

replacement was purchased, but it doesn't fit, that would explain it's

present state. 

 

Robert


Edited by clamchip, 07 January 2021 - 09:09 PM.

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#28 Myk Rian

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Posted 07 January 2021 - 09:26 PM

The 2 lenses, don't lose the spacer tabs on the one. It goes on top of the other. Look for witness marks on the sides of the lenses and align those together.

Don't over tighten the cell when you put it back on the tube. Just snug.

 

That scope has a good reputation. I have a similar Meade that is great for planets with a 5mm WA EP. DSOs not so much. My dobs do those.

 

Here is your scope mentioned in another thread.

https://www.cloudyni.../#entry10786198


Edited by Myk Rian, 07 January 2021 - 09:31 PM.

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#29 Kasmos

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Posted 07 January 2021 - 09:33 PM

I have a question for the Edmund owners and the OP. Don't these scopes have a cardboard inner tube holding the baffles? The reason I ask...If you look at the photo in post #14 looking into the cell, it looks like the cardboard or something brown comes all the way to the front of the tube.

 

If it was mine I'd take the cell off the tube and inspect it to check the lens fit then come up with a idea for a retaining ring. One option might be to make a ring out of a plumbing part or a rolled band of aluminum or steel, and hold it in with 2 or 3 small set screws from the outside of the cell.


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#30 Druchti

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Posted 08 January 2021 - 12:29 AM

The lenses seem to fit into the cell fine so I'm guessing they are the right ones ..do those dot witness marks look like any other ones you guys have seen? Just wondering if it maybe could be an off brand replacement like u guys mentioned from the originals braking..the couple edmunds I have found in the forum data base had arrows on the lens edges not dots like mine. I do have a machine shop nearby I might stop over at and just see what they would charge. How thick should the ring be? Same as the lip that holds the back of them?  And is the mating surface of the ring just flat or does it have to have a angle to match the shape of the lens?  If they are to expensive I'm going to explore some of the other ideas you guys have brought up 

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Edited by Druchti, 08 January 2021 - 12:32 AM.


#31 TSSClay

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Posted 08 January 2021 - 10:02 AM

It might be a lot cheaper for the machine shop top make an unthreaded retainer ring and hold it in with screws from the outside.  In any case they should have some good suggestions.

 

Best Regards

Clay



#32 ccwemyss

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Posted 08 January 2021 - 10:30 AM

If you don't mind losing a little aperture, and if the cell is really 4" diameter, you could buy a 1" length of 4" aluminum tube from a place like MetalsDepot (about $13), drill three holes in it, tap them and put in short set-screws to press against the inside of the cell, so you don't have to modify it. 

 

Chip W. 



#33 PawPaw

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Posted 08 January 2021 - 10:57 AM

The Edmund lenses are extremely difficult to remove and reinstall in their cell because how they are attached to the OTA.  I know from experience the odds are not in your favor if you leave the cell attached to the OTA and try to remove or install the objective.     I have successfully removed the objective from the OTA by pointing the OTA up (objective to the ceiling) and removing the 3 nuts then pushing the bolts through so they fall inside the OTA.  You can retrieve these later.  Then simply pull the cell off the OTA.  My remedy to install was to glue simple nuts (not the original acorn nuts)  on the inside of the OTA being held in place with the bolts while they set.  This way you can slide the cell on the OTA and simply screw the bolts in from the outside.  This is how most objective cells are designed.  

 

All of the 3 and 4 inch Edmund objectives I have seen have stamped numbers and arrows.  Sometimes they actually have  instructions stamped on them showing which is the flint and crown and stating the correct orientation.  Your objective could be an Edmund but I don't see any stampings on the edge.  With that said as long as it fits in the cell I would do the following to replace the lost retaining ring.  

 

Fashion a piece of plastic either PVC or even a flexible piece of plastic and cut it so it is the same size and radius as the retaining ring but that will fit inside the metal cell and lightly touch the internal threads.    You want this plastic ring to slide down and lightly touch the objective.  You don't want any pressure on the objective.   Before gluing check that Newtons rings are centered and concentric.  Then apply a small amount of adhesive glue in 4 equal points on the plastic ring to adhere it to the metal cell.  Use a type of glue that can be removed later if needed.  For testing purposes you could use kapton tape to hold the retaining ring while testing...Then apply the glue if you are satisfied with your results.  

 

 

Here are a few pics of my Edmund 4 inch objective and  cell.

 

Cheers

 

Don

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Edited by PawPaw, 08 January 2021 - 11:04 AM.

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#34 clamchip

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Posted 08 January 2021 - 10:58 AM

Where the retainer ring contacts the glass it's flat and smooth.

And when screwed in fully probably flush with the edge of the cell.

It should have a slot cut across the ring both sides for remove

and install.

The wall thickness should be as thin as practical to get the 

most clear aperture.

 

Robert


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#35 davidc135

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Posted 08 January 2021 - 11:40 AM

The spacers should be 120degrees apart.  David



#36 telescope200

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Posted 08 January 2021 - 03:38 PM

Attached is a 1969 Edmund catalog listing for what looks like your model scope.  There are later models but yours is this earlier version with the tube bolted in place. Unless you haven't posted all the parts you have it looks like you are missing a counter weight, it takes two and yours needs the 90 degree mounted weight to change balance, tube is fixed/bolted so you can't slide it to change balance point. Later models  put the two weights on one shaft, eliminating the 90 degree shaft, and had a strapped on tube so you can slide it for balance.

 

You could add weight lifting weights above the one you have to balance it. You can also add little weights to one end or other of the tube to balance that.

 

Surplusshed.com and eBay have cheap focusers, they are for 60mm and 80mm tubes, you would have to make some kind of adapter. Also the Edmund focuser tube looks longer so you may have to go to the hardware store to buy 1.25" chrome sink drain pipe extensions to make it longer. Sink drain comes pre-flared and fits an eyepiece.

 

Hope this helps,

 

Robert S

 

 

Attached Thumbnails

  • Edmund 4 inch refractor ad 1969 b.jpg

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#37 Starman04

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Posted 18 January 2021 - 05:04 PM

Nice find.  I was looking for a threaded retainer ring a while ago and came across this site.  Not sure if they sell to individuals but it's worth a try if your cell has the threads to take a ring.

 

www.thorlabs.com/newgrouppage9.cfm?objectgroup_id=1535




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