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Restoration of Criterion RV-4 Deluxe

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#26 DAVIDG

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Posted 14 July 2019 - 07:12 PM

    Out to the shop and out came the hack saw. I sawed the mounting plate for  the diagonal off so the cut was parallel to the stalk. That allowed me to slide it down about a 1/4" and still have  a good amount of  metal overlapping. I used JB Weld to epoxy the two section back together. To hold them  together I used a welder's trick of using a magnet. I covered the magnetic with painter's tape  since the tape will allow me to remove the magnetic if some of the epoxy gets on it.  I also embedded a small washer in the epoxy that bridges the cut to add strength. Once this side is cured I'll epoxy the other side were the magnetic is.  That should make the joint plenty  strong enough to hold the mounting plate in place and I'll be able to glue the new diagonal on and get it the correct location.

 

                       - Dave 

 

rv4fixingdiagonal.jpg

 

rv4 fixing diagonal2.jpg


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#27 TOM KIEHL

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Posted 15 July 2019 - 07:15 AM

Dave , I know you most likely took into consideration the optical tube wall thickness before this modification . Didn't you ? question.gif



#28 DAVIDG

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Posted 15 July 2019 - 08:52 AM

Dave , I know you most likely took into consideration the optical tube wall thickness before this modification . Didn't you ? question.gif

  Hi Tom,

      In my posting a few messages back I stated the ID of the tube is 4 1/2" and the line across the top of the template is showing  were the template is located vs the ID of the tube. When positioned so it is  at the ID of the tube, the template comes right up against the mounting surface of the diagonal holder You can see in the second picture of the modified diagonal plate that the line is now below the mounting flange of the focuser, which is now taking into account the thickness of the diagonal  and will place the reflective surface at the correct position, which in on the optical axis of the primary.  The bottom line is that the casting was made wrong just like the other black tube 4" Dynascope I restored a few years back and the stalk to hold the diagonal is too short  since it doesn't take into account the thickness of the diagonal. 

   If you measure were the center of the reflective  surface of the  diagonal is on your Deluxe, I bet you'll find it is less then 2-1/4 from the ID of the tube. If so then it is too close to the focuser  and too far forward.  So to make it look like the scope is collimated you had to tilt the primary upper ward toward the focuser which introduces astigmatism into the image. You won't notice the problem at low to middle power but when you turn up the power and say look at Jupiter the planetary detail will be soft and you never get the full potential out the primary.  

   The focuser defect and the poor optical quality of the diagonal really hurts the optical performance of my scope which if built correctly would give amazingly  sharp images.  

   

 

                             - Dave 


Edited by DAVIDG, 15 July 2019 - 08:58 AM.

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#29 DAVIDG

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Posted 15 July 2019 - 09:11 AM

 Here is a  link to when I restored my late 50's Criterion 4" Dynascope that had the same diagonal mounting problem. https://www.cloudyni...rion-dynascope/

 Here is another link were another Dynascope Deluxe owner found the  same problem. So it is  a manufacture defect in the design of the focuser/diagonal mount. https://www.cloudyni...nascope-deluxe/

 

               - Dave 


Edited by DAVIDG, 15 July 2019 - 09:21 AM.


#30 TOM KIEHL

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Posted 15 July 2019 - 09:19 AM

Thanks for the second clarification for me , Dave . With my ADHD sometimes things go right by me lol.gif waytogo.gif


Edited by TOM KIEHL, 15 July 2019 - 09:20 AM.


#31 Chuck Hards

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Posted 15 July 2019 - 09:22 AM

Nice work, Dave.

 

I'm saving this restoration for retirement.  I saved the parts from a seller who was parting-out the scope a few years ago, unfortunately they had already sold the tripod to someone who made it into a lamp.  Luckily I had a spare Criterion pedestal on-hand.  Tom K. kindly drew-up the tripod parts for me so I may build a reproduction one of these days.  Only two castings to make patterns for, the leg brackets are sheet-metal work and not too bad a task.

 

RV4 001.jpg

 

 

 


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#32 DAVIDG

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Posted 15 July 2019 - 09:32 AM

 Tom,

   No problem.  Please note I'm not Criterion bashing when pointing out the diagonal mounting defect. With doing 35 years of scientific research it is just a habit to check and double check everything. So when the measurements for the position of the diagonal didn't make sense I double checked them and made a template as another check. Bottom line is that the designer of the casting missed the point about the thickness of the diagonal and/or didn't understand the optical principles of how the optics work in a Newtonian. 

   If you think manufactures mistakes in telescopes are bad, just get into car restorations ! 

 

                                   - Dave 


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#33 TOM KIEHL

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Posted 15 July 2019 - 12:19 PM

Dave , it appears that there is a design deference in your slo mo Dec. control , from Chuck's and mine . Can you explain why , Early as compared to a Later  production date  maybe ? That might explain differences of  optical tube placement in the tube rings ie. weight and balance point .

 

Maybe it's just an Optical Confusion due to image angle capture ?


Edited by TOM KIEHL, 15 July 2019 - 12:29 PM.


#34 DAVIDG

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Posted 15 July 2019 - 12:42 PM

 Tom,

   I think that yours and Chuck's have a DEC slow motion assembly that looks to use the same components has the RA drive with the motor replaced with shaft with knobs on the end to manually turn the worm. I think this was used later on in the production. 

    Mine is bit different in that is has a smaller gear that is mounted to a  brass sleeve.  The sleeve has the same type of  "T" shaped cut in it that the eyepiece tube has. The sleeve fits over a bushing that has knurling on the outside and set screwed in place to the Dec axis.  So the ID of the brass sleeve is contact with the knurling of the bushing. If you have an RV-6 it is similar in operation to DEC axis lock used on them that uses a split piece of copper that gets clamped around the Dec axis when you tighten the thumb screw.  

  All this is inside the housing that is attached to the DEC casting.  There is a small thumb screw  on the housing that when tighten push down on the OD of the brass sleeve which causes it to tighten down around the bushing with the knurling. So when you turn the shaft with the knobs on both ends , that  turns a worm that  turns the gear attached to the brass sleeve which moves the scope in DEC.  Loosen the small thumb screw and Dec axis is free to rotate in the brass sleeve  so you can make course  movements in DEC.  

 

                 - Dave 



#35 TOM KIEHL

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Posted 15 July 2019 - 12:51 PM

Dave , would a Serial Number reflect a production date ? ......... My Serial Number is .... 951



#36 DAVIDG

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Posted 15 July 2019 - 02:04 PM

Dave , would a Serial Number reflect a production date ? ......... My Serial Number is .... 951

 Tom,

    Mine just say "RV-4" on both the tube and the mount. Unfortunately the motor has no date.  

 

                     - Dave 


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#37 Compressorguy

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Posted 15 July 2019 - 04:02 PM

Those legs and especially the upper leg mounting brackets sure look like Celestar! or is it the other way around? Lol

 

 

Much prefer the spikes on the Criterion version. They just look more robust and refined than the Celestar version. 


Edited by Compressorguy, 15 July 2019 - 04:05 PM.


#38 DAVIDG

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Posted 15 July 2019 - 04:09 PM

Those legs and especially the upper leg mounting brackets sure look like Celestar! or is it the other way around? Lol

 I have  a couple of spare Fecker Celestar brackets for  the connection between the tripod legs and the center hub and they are exactly the same was what is on the Criterion. I bet Criterion  used the same company to make the legs as Fecker. The wooden legs are a little different in design with the metal spikes at the end of the  Criterion legs. They look more like what is found on survivors tripods 

 

                   - Dave 


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#39 DAVIDG

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Posted 19 July 2019 - 09:14 AM

  A few days ago  I  added more epoxy to the joint that holds the correctly positioned mounting plate for the diagonal.  Last night I cleaned up the epoxy and sprayed the stalk and the inside  of the focuser tube flat black.  Attached is a  picture with my template in place that now shows the mounting plate is positioned to take into account the thickness of the diagonal. When the diagonal is mounted the reflective surface will be in the middle of the tube and exactly on the optical axis of  the primary. So the center of the field will now be located in the exact center of  the focuser . This will also allow  the optics to be correctly aligned with no tilt to them and hence no induced astigmatism. 

 

                         - Dave 

 

RV4modifiedfocuser.jpg


Edited by DAVIDG, 19 July 2019 - 09:14 AM.

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#40 DAVIDG

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Posted 21 July 2019 - 11:09 AM

 Yesterday I installed the new diagonal onto the modified stalk on the focuser.. It is now in the correct position  in the optical path. I used a laser collimator to get the alignment dead on. I put the mirror cell back in the scope with the primary. The cell has a brass cap that can be removed for ventilation so a placed a piece  of tape over the hole with a mark that show the center of the cell. With the laser in the focuser it was  a simple task to align the focuser so the beam hit the spot on the tape.  The primary was installed back in it's cell and it only took a few more minutes using the laser to get things perfectly aligned.   I know this was the first time ever that the optics were correctly position in the telescope and correctly aligned. Now I just had to wait for the stars.

  Around 8:30 pm I was able to pick up Jupiter in bright twilight. It was razor sharp with  a 28mm eyepiece, a good start but I have said that is not a  critical test of optics, so I switch  to 7.4mm eyepiece That image was still very sharp and when the seeing snapped a lot of detail visible in the cloud bands. Then I notice a tiny black notch on the limb. I watched  over the next 15 minutes as  it turned into a sharply defined circle from one of the moon's in transit.  It finally got dark enough to see the stars so I swung over to Vega to do a star test. Perfectly   round out of focus images with the same pattern on both sides. No astigmatism like I had before.  I know this was the first time ever the star showed images like this in this telescope.  In focus,  the stars  at this magnification were showing beautiful text book Airy disks a with single diffraction ring. The Double Double was textbook, cleanly separated  with four perfect Airy disks. 

    So with a little attention to detail, and some epoxy and solder I turned a barely functioning telescope into a precision optical instrument. I'll have it up at Stellafane so those that come up can judge for themselves. As I keep saying telescopes need to be looked through just as much as looked at so those that restore them should  pay as much attention to the optics as they do the mechanics  and not assume that the optics have no issues. 

 Here are couple of pictures showing the alignment and the finished scope.

 

 

                 - Dave 

             See you all on Breezy Hill in a few days !

 

rv-4 alignment focuser.jpg

 

RV4 looking down tube alignment.jpg

Attached Thumbnails

  • rv4 finished scope.jpg

Edited by DAVIDG, 21 July 2019 - 06:52 PM.

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#41 DAVIDG

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Posted 28 July 2019 - 09:27 PM

 It just relearned a lesson I should have known.  When I glued the new diagonal in place I first used double sided tape to get the position correct then used clear Gorilla Glue around the edges to firmly glue it in  place. What I didn't realize was how firmly. The first night the images were just great. Then a few days later I noticed some astigmatism, I thought the primary might have got a little out of alignment. This Friday I had the scope out for one last shake down before I head to Stellafane. The images were awful with this wacky astigmatism. The  image looked like it had double coma, two tails !  I was in  the backyard at 1 am with two different laser collimators and getting eaten by bugs trying to figure out what  was the problem. I finally  gave up and called it a night. I got up on  Saturday and pulled the focuser/diagonal out of  the scope and decided to test the diagonal with it glued in place. Well in 30 seconds I found the problem. This modern day super strong glue had cured and put so much force on the glass that the flat surface was twist up like I never had seen !  I had to carefully cut the glue away and pry the diagonal off the metal mounting plate. Once off it tested back to nicely optically flat.  So today I glued it back on but this time used the method that I had been using for years, that is using RTV with a thin piece of cardboard between a layer of RTV on the metal plate and one of the glass surface of the diagonal. After it set I tested the optical flatness again and it was unaffected and nice and flat. Back in the scope and I just got done checking the scope out on the star. It is back to showing beautiful round Airy disk with a single diffraction ring. 

 

                    - Dave


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#42 DAVIDG

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Posted 10 August 2019 - 09:53 AM

 I had great time with the RV-4 at Stellafane. It was giving beautiful images showing Airy disks and easily splitting double stars. The drive was still giving me problems thou. When adjusted so it would track there was a fair amount of play so you had go past an object and come back to it . So I dug back into the drive to try to figure out what was the problem over the last few days. . My RV-6 has the same drive and when adjusted correctly works great. Just center up an object and let go of the scope and it tracks. On the RV-4  if  I adjusted the worm so it meshed well with the main gear , the motor would jam. So I took the motor off and made a tool from a brass rod with a slit  cut in the end and knob on the other so I could turn the worm by hand. The idea was it would allow me to feel when the worm was correctly adjusted so it turned freely and meshed  correctly with the main gear so there was minimum amount of play.  It tried for a good hour to find the correct position but as soon has the worm was adjusted so it had very little play it would jam when I rotated it about 3/4 of the turn. Then it hit me, I bet the main drive gear was installed backwards. The main gear has the teeth cut on  a slight angle and the worm is cut with the matching angle was well. This is done to minimize backlash.  So I took clutch assembly off and flipped the main gear around. Within a minute I knew that was the problem! The worm now rotated smoothly and I could adjusted so it meshed well with the main gear with very little backlash.  I put the motor back on and  took  the scope out. I  observed Saturn and the Double Double both of which stayed  in the eyepiece for 15 minutes as I was  observing them. 

    This looks like another mistake from  the factory since the drive never worked from day one, since I found the original grease on the worm that was never smeared out and the gear inside the motor  not attached to the output shaft.  So when I look at all the evidence, what happened  was the main gear was assembled backwards. That caused the worm to jam, so as soon as the drive was turn on for the first time. That caused  the gear in the motor to  shear loose and the drive never worked.  

   So for the first time the scope is now working as advertised. It is a  shame that it had these major defects in both the drive and optics  because it cost $159 in early 1960's dollars and most likely was used only few times then spent the rest of the time in a  damp basement. 

    So again the lesson learned is  don't assume anything that you find on the these old scope is way it is supposed to be and don't be afraid to change them so the scope will work. My philosophy in restoring a telescope, clocks, vintage electronics and cars is making them as pretty to  use as they  there are pretty to look at.  

 

 

                        - Dave 


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#43 tim53

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Posted 10 August 2019 - 10:22 AM

I'm having a hard time picturing this.  Wouldn't the angle on the teeth be the same with respect to the worm if you flipped the worm gear around?



#44 apfever

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Posted 10 August 2019 - 05:23 PM

Yes, flipping the main gear won't change the angle of the teeth or any number specs. On the practical end, flipping the gear CAN change the mesh due to small variances that are not part of the specs.  An example would be a nut that goes on a bolt smooth one way and very rough ( or not at all) the other way. 


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#45 DAVIDG

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Posted 10 August 2019 - 08:50 PM

 There is something very different in the pitch because with the gear the way it was originally positioned  I could only get  3/4 of turn of the worm when it was fully meshed but when I flipped  it it turned smoothly through  many rotations both forward and backwards. I turned the worm many many times so  the main gear went thru at least 270 degrees of  rotation with no binding yet with the gear in original position I could only turn the worm 3/4 of a rotation and that resulted in about 1 degree of rotation of the main gear before it locked up hard. Like I said I spent  a good amount of time trying to find a position of the worm/motor assembly that would work but couldn't but within minutes of flipping the gear it was working just fine. 

  The fact that diagonal was of poor quality, the length of  the stalk that holds the diagonal was wrong and the issues with the drive,  all point to a  lack of quality control. What is sad is because of  this the scope looks  it was barely used and the owner could have lost interest in astronomy because of it. It was donated to the observatory and sat in the  corner for at least the last 15 years because it didn't work Again this was an expensive scope back in the early 60's and these problems would have be difficult and expensive to have addressed by the original owner trying  to deal with Criterion.  Long distance phones were not cheap  at least I remember my parents acting that way  back then and shipping the scope back would also  have been expensive. 

   My message continues to be don't take anything for granted with these vintage/antique scopes.  You never know what was done in the past to them and they never could have been right from the start. 

 

                - Dave 


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#46 Bill Griffith

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Posted 11 August 2019 - 01:00 PM

Side note suggestion. 

 

On drives that may not have conveniently removable gear sets  Clover Compound (lapping compound) may be an option.

 

It is a little messy cleaning the drive gears between grit coarseness but, worth the results especially when other component like AC motors for a particular system is impossible to find. 

 

Clover Compound comes in as many grit levels as sandpaper.

 

Bill


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#47 DAVIDG

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Posted 11 August 2019 - 05:16 PM

 I had the scope  out again last night. The tracking is now working well. The images are great with very nice Airy disks around stars. It was having  no problem splitting tough doubles.  If the scope had a soul I'm sure it is happy to be finally working like it should and being used under the stars instead of  living in a damp basement or the corner of the observatory gathering dust. 

 

                 - Dave 


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#48 Senex Bibax

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Posted 12 August 2019 - 06:20 AM

"My philosophy in restoring a telescope, clocks, vintage electronics and cars is making them as pretty to  use as they  there are pretty to look at."

 

My personal philosophy is the reverse: First make them pretty to use, then worry about the looks. If you see the 62 year old Lambretta scooter in my garage you'll know what I mean..



#49 DAVIDG

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Posted 12 August 2019 - 09:00 AM

"My philosophy in restoring a telescope, clocks, vintage electronics and cars is making them as pretty to  use as they  there are pretty to look at."

 

My personal philosophy is the reverse: First make them pretty to use, then worry about the looks. If you see the 62 year old Lambretta scooter in my garage you'll know what I mean..

 I think we have the exact same philosophy since making them work like they should vs how they were made  is my number one goal even when that means modifying them from their original condition. As with this scope I fixed manufacturing defects that would not allow the scope to perform like it was meant. On others I have also refigured the optics. That is not a sin in my book because I now have a  scope that gives great images.  In my book it does no good to match exact paint colors, screw types, wood finish  etc so the item looks perfectly original but barley works. The designer didn't mean for it to be that way and the same is true with this RV-4, just read the original ad which states great optics, wonderful views and tracks well.  I just made it the way it was meant to be. The result is a good looking telescope but more important a great performing telescope.

 

                     - Dave  


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#50 Chuck Hards

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Posted 12 August 2019 - 09:54 AM

I didn't know it was EITHER restore it faithfully OR make it work well.  To me, you do both to the best level you can.  Why is this even an issue?  


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