20 replies to this topic

[Optics Patent]

I recently acquired my oldest Questar (unless my double-digit Field Model is older - that model was released in 1956).  While in good shape as received from the Ebay seller, it needed some service, including both drives.  This was a buy-it-now that just had a major price reduction to the price presciently suggested by Steve C. when it was asking $500 more.  The drive service needs provided a further adjustment.  The price was right with consideration of the needed work.

 

This was a 1961 factory refurb of a 1957 scope, with all the upgrades to the modern prism.  It included original Braymer-signed documentation of the sale.  It appears never to have been serviced since the 1961 sale - this was not a sent-in refurb but a sale to a new customer of a used and refurbished scope.

Many little observations:

• The back plate (not normally unless peering through the axial port) is synthetic material, not aluminum.
  
  
  
  
  
  
   

• One control box screw hole was stripped, but this doesn't seem to affect stability.  If I were hanging a big camera on it (unlikely), I might look at fixing the hole, but I'm not sure how besides tightening up the hole with some fibers before inserting the screw.
   

• The lower control box screws were not the usual short Bristol screws, but longer slot head screws that match those of the barrel rotation brakes - but slightly different length.  Factory said this is probably correct.  I didn't dig forward of the back plate into the barrel to see what they engage.  Perhaps the stripped screw (a short top one) hints at the issue.  Note that the finder mirror bracket appears painted, not brushed as in later examples.
  
  
  

   

  
  

   

• With the synthetic back plate, there is no need for the gasket between the ring and the back plate to avoid metal on metal sliding contact for barrel rotation.
   

• One original logo badge popped off with my suction-cup method, and the other required some heat before the suction could pull it.  The turntable hub cover was attached by gummy double stock tape and needed heat to soften.  The arm hubs were attached with brittle adhesive.
   

• This has the old firm focus action.  Only slightly firmer that the light focus action we're used to and still smooth after greasing.  One might not notice the difference if unaware, and one who had never experienced Questar focusing would find nothing firm about it.
   
• All the grease had failed, and was hard and brown.  This was especially an issue in the control box, where the action of both levers was hard and scratchy.  New grease made everything buttery smooth - as good as it gets.  This was especially a surprise for the finder prism shuttle, which in this era lacks the plastic bushings that I have found in all later examples.
   
• The base interior displayed the factory modification to provide the central tripod mounting hole.
  
  

   

• The base had an unexpectedly shallow rim around the RA ring, so that the upper surface of the ring is above the rim, unlike every other one I've seen.  The ring appears original (dark blue) and has the same thickness as other examples I had on hand.  Because the plastic pips that the ring rest on add 0.040" above the floor below the ring, I instead adhered eight Teflon spots (made from Questar 0.005" Teflon sheet used in the declination drive stack) and this gave a happy result.
   

• Unlike every other RA drive, the platter that the RA ring surrounds and the drive discs rest upon was not pinned to the main gear.  Factory confirmed that the friction is adequate to prevent slipping when the axle is under tension (if it slipped here, the RA setting would be lost).
   
• The base displayed a brushed appearance.  Almost a machined look, and the brush lines were perfectly concentric, not the result of a hand sanding job.  My view of early photos shows a somewhat brushed appearance, but the factory said they considered all models to have been polished.  I decided to limit my work to polishing only, instead of sanding out what I believe are original factory markings.  This is the result:
  
  
  

Because the dew shield did not appear to be original to the scope (somewhat faded purple) I prefer to display this with its original blue moon map.  Note that north is up and the view is not reversed because the original prism would provide an unreversed image.  I have no hope of ever getting a nice early blue dewshield, but the 1990s shiny blue dew shield is an acceptable substitute to coordinate with the RA ring, even if the older blue was slightly less greenish and more indigo (very handsome!).

 

[Optics Patent]

I just received another 1957 Questar.  This was an AM auction. It advertised a bad mirror, and had some other distress signals.  The real oddity is that aside from the blue dew shield (etched to distinguish from 1990s and desperately needed for the above 1957 #303 - as the seller confirmed before I bid) it looks like a much newer scope.  Something of a mystery.

 

Many factors are non-1957, and this is verified by a comparison with a model nine serial numbers later/newer (and sold in 1961 as an updated refurb):

• Arm logo badges are 1960s-70s
• RA ring is bright purple (1960s)
• Moon map is bright purple.
• Focus knob is modern type (not flanged).
• Star diagonal and wide field upgrade with large modern axial port aperture.
• Base plate is pristine aluminum, not black synthane - I may be mistaken on whether they had switched to aluminum by then.
• Back plate is also aluminum, not synthane as is my #303.

It's as if sometime in the mid-late 1960s the owner sent it back and asked them to update it in every respect.  This hypothesis requires us to believe that the factory removed the moon map and replaced it - perhaps the old one was badly faded? 

 

Although the scope was well-packed inside the original case, I was deeply disappointed that a respected telescope retailer would pack a Questar so poorly.  The case clunked loosely in the outer box, which was crush-damaged:

 

 

Opening revealed that the carton was filled with deflated pillows that any capable shipper knows are not intended to support heavy objects but are intended only to fill voids with light objects.  Pillows are not for supporting heavy items, and will deflate in transit.  $5 saved in bubble wrap by reusing old pillows - I won't know whether any of the exterior case damage was from rattling around.  This images shows the freshly-opened package with no packing removed.  Most of the pillows were airless and flat.

 

 

Happily the dew shield that motivated the project was in good shape, with one edge ding I was able to resolve nicely.  You can see that the purple ring and moon map are no match for the star chart - I plan to replace the star chart with a nice purple one that matches to add value to this scope while completing my old 1957.  I also note that the moon map doesn't have the light lavender shade I've seen on many earlier ones that are obviously not faded in the sun (with light and shadowed areas contrasting).  The ring is really a stunning purple!

 

 

Looking inside, I saw a questionable spot on the corrector over the secondary reflector (it's at 10:00 in this image, near the edge).  Not a surprise, but that means that both elements might need to be recoated.  Yet that spot wasn't on the slivered front surface but on the rear.

 

 

I did some work on the dec drive after popping off the badge, and got the sticky, jerky slewing to smooth out.  Happily neither drive needs to be serviced with new discs - that makes me think it's been serviced, and little used since.  The factory reports nothing more than a 1957 build.  The mirror had an intriguing anagram of the serial number: P-7492 (scope is #7-294).  The factory assured me this was coincidence and not a "clue."  The motor verifies the 1957 build with a "4-1956" date code:

 

 

The polished surfaces are very nice, and a little had polishing without too much effort made them shine nicely.

 

The real drama was in getting the barrel apart to remove the mirror.  It wouldn't budge the normal way: gripping the control box in one hand and turning the barrel in the other.  So I took some time to build a fixture.  Using a plate of clear plastic I had on hand I drilled holes where the four control box screw enter the back plate, and one clearance hole for the focus rod.  Using the longer screws from the rotation brakes, and with all the prism assembly removed, I secured it and clamped the plate to the bench.

 

 

With both hands using all my strength and the plate anchored down, it wouldn't turn. 

 

With my largest strap wench down at the base to grip the thickest part of the tube to avoid denting, it wouldn't turn as hard as I dared torque it.

 

I used a heat gun to try to break down adhesive and got it good and hot.  No luck.

 

Then, I got an idea. An awful idea. ("The Grinch got a wonderful, awful idea!")  Just as The Grinch had to take Cindy-Lou Who's Christmas tree back to the shop to fix a light, I decided to remove the mirror out the front after removing the corrector - I usually save the corrector removal for after I have the barrel separate from the back plate.  Stop me now if you see the obvious problem with this approach that eluded me.

 

Corrector removal was a minor challenge, but some debonder (recommended by a friend here and purchased providently without an immediate need) and some tapping with a brass hammer on the spanner did the trick.  I'm going to use the tapping technique to controllably break it loose instead of the quivering high-torque approach (requiring an assistant) I have riskily used in the past as shown alarmingly in one of my videos.  The very good news is that the coating problem on the corrector actually went away with some determined rubbing with an alcohol-soaked Q-tip.  That avoids 2/3 or more of recoating costs.

 

Now, back to my awful idea - to remove the mirror I just had to turn the focus rod until it disengaged from the base plate and remove the thimbled mirror out the front opening.  My idea was so awesome I decided to video the process.  The mirror disengaged, and I reached in from the front and lifted the spindle off the thimble.  As I elevated it carefully the horror swept over me - the mirror is larger than the opening of the front cell!  And no, turning it sideways doesn't reduce the diameter.

 

This was the deepest doo-doo I'd been in during my few years dismantling Questars.  It wasn't realistic to get the thing back together with the three springs loose and focus rod not finding its way back into the hole.  So I dismantled the back plate from the back ring (removing the four flat head slotted screws and tapping to separate the two parts) to access the springy clutter inside. 

 

 

This was better than tuning a carburetor through the exhaust pipe, and I was able to reassemble the spindle to the thimble and get all three springs nicely seated.  Now, I was back where I started.

This time aided by more heat and the debonder, and some time to soak, I went after it with all my might, risking a barrel dent.  leaning and bouncing against it with my body weight finny broke it free (no dents).

 

Everything went smoothly from here, with the mirror out to show its colorful coating failure:

 

 

It's already off to Majestic (new VA address) for a $65 recoat.  My toddler helped pack it up, and left a buttery fingerprint and toast crumbs.  He's learning how when we can't fix things ourselves we pack them up to have the mail carrier bring them far away to be fixed, and then a box will come back with it all shiny and new.  He saw the carrier take the box and gave a smile and a wave.  Someday, Leo will have his own Questar that he restored with Dad!

 

The vintage blue star chart looks perfect on the other true-blue 1957 scope:

 

 

 

 

 

 

[daddymouse]

I envy your knowledge and expertise!  Good luck, and please keep us informed!

[Toddeo]

Ben, why did Questar mix the colors on the tubes, dew shield and base ring? Wouldn't you think that if they sell a Questar with a Mystic purple tube and dew shield, they would also have a purple ring? I ask , because I have a '69 standard with the purple tube and dew shield- but the ring in blue.

[Optics Patent]

Toddeo, I can first note that the factory confirmed that this 1957 was in for updates and service in 1972, which is clearly when it was modernized and "purpled."

 

The best rule for color and design issues is that the factory will use whatever is current, and does not typically have a back-stock of vintage parts for service.  That means that while they may try to conserve things like vintage badges, they will replace with current when needed.  Assuming the 1957 owner was unhappy with faded blue color and wanted a modern look, he probably preferred the then-modern purple.

 

Yours might have needed a ring replacement in the 1990s (dark shiny blue) or more recently (matte lighter blue).  If your replacement ring was 1998 or earlier it's the old 0, 10, 20, 30, 350 type and if newer it's the 0 20 40 0 20 40 type.  Post a pic?

 

This type of mystery and how each scope reflects its history is part of what I enjoy about this hobby.  Finding ways to restore (especially when both scopes in a swap are improved) is also a joy.  Restoring the first 1957 means I can complete the 1972 update to the second one.

[Toddeo]

Ben, my '69(almost mint) Questar was sent in for service on 6/17/2017(previous owner). The ring might be purple, but not as much as on your scope. It seems to have a lot to do with the lighting. Before I took these photos- it looked dark blue.

Attached Thumbnails

• 
• 
• 
• 

[Optics Patent]

Toddeo, from what I clearly see, you can be assured that you have the correct original factory colors for your scope.  With different materials and finishes for each part, not to mention how they can catch the light, there is normally a variation in the appearance.  I haven't been able to figure out why the norm is a different shade for the moon map and the start chart.  I think the different color of the printing is a factor, but there are real differences I see again and again that can't be explained by fading of replacement parts.  Your slightly "lavender" moon map is consistent with the era and a few I have - unfaded but clearly a different purple than the moon map.

[Wisconsin Steve]

Another neat project Ben and restoration! You need to retire from the attorney biz and set up a Questar restoration business...

 

Steve

[DAVIDG]

Ben,

    Have  you thought about testing the optics in all the Q's that pass through your hands ? It is easy to do and will give you and us some very interesting data.Plus it allows one  to get the alignment dead on without  having to have the scope under the stars. You can easily test the primary while stilll in the tube by removing the corrector and Foucault/Ronchi testing the primary. The whole system can be tested by double pass autocollimation using a 4" optical flat and simple to make  Ronchi screen/light source that replaces the eyepiece.

   By the way did this Q look to have the origianl optics with the secondary on the front of the corrector or were they changed out to the newer vesrion with the spot on the back of the secondary ?

   The story goes that Cave was making the primaries and the correctors were made in Japan. If that was case then they were not matched like Cumberland  is doing so the older one are said not have the same optical quality as the Cumberland optics ones. So testing would show what was really going on.

 

                      - Dave 

[Optics Patent]

David it is definitely my goal to have a good test setup to evaluate scopes. For instance I have several Field models and would want to pick the best to pair with a Duplex mount. Or more absurdly to pick the better Fast focus for the left side as my right eye is nearly blind.

Of course to quickly test new arrivals to quickly spot a dog without awaiting a starry night and weighing seeing - though an artificial star would be helpful.

For reselling to friends here I’d be able to certify the goods ones akin to the vague “typically excellent Questar star images” I might also state. Any dogs could be ebayed with caveats.

This has the secondary on the front so optical are presumably original. I didn’t even bother star testing with the bad mirror coatings but I always should so I can tell if reassembly introduces a new alignment problem.

[Optics Patent]

For the testing I’m disinclined to dismantle to test only one component but it’s a good capability to have when I’m going to dismantle anyway.

I’m very interested in the alternative. What auto collimator would you advise? I’d start with a full solar as the optical flat.

[DAVIDG]

 Autocollimation is a  technique vs a device.  You need an optical flat that is optically smooth but  it doesn't need to super flat. One is that is many waves from flat but smooth will add about 1/50 wave of error to the result. Get one that is 1/4 wave flat and the error is too small to worry about. You then need to make simple "eyepiece" which is  a Ronchi screen with around 100 lines per inch  and small LED that is glued to the screen just slightly off center. This is then mounted in a 35mm plastic film holder. 

   You point the scope at the flat and align to the flat which is easy to do, especially with a Quest that can be setuo and table and use the slow motion controls. Once aligned the Ronchi screen eyepiece is put in the scope and you focus until you see three Ronchi bands. The shape of the bands indictates the optical quality.  Excellent optics that are at least true 1/10 wave will show dead straight Ronchi bands. 

 There are many messages and threads that discribe how double pass autocollimation testing is done here at Cloudy Nights and what the results look like.

 

                          - Dave 

[rcwolpert]

Ben,

Here’s a thread that shows how I made and used DPAC testing equipment.

https://www.cloudyni...dpac-territory/

 

Bob

[Optics Patent]

I'm still left with many questions, as the posts assume lots of knowledge I don't have.

1. Ronchi grating.  Am I really paying nearly $200 at Edmunds?
2. LED.  There are multitudes of variations - all I can surmise is green.  Brightness?  Optical form?  A domed clear lamp will focus more light, and a flat face lamp will act as more of a point source.
3. "Glued to the screen".  Which side?  The photo makes it look like the LED is in the film canister cap, over an inch from the screen, on the tail end away from the optics so the LED light passes through the screen.
4. Where is the observer?  Adjacent to the scope with some distance to the optical flat?  "Double pass" seems to suggest that the observer is viewing through the scope.

I'm hoping for a shopping list and an unambiguous assembly and use instruction set.

[rcwolpert]

1. Get the Ronchi screen here: http://www.ronchiscr...com/screens.php   $9.75 for the 133 LPI

 

2. Get the LED here: https://www.amazon.c...,196&sr=8-21   

Best to scuff up the bulb a bit with sandpaper to diffuse the light a little.

 

3. Battery holder: https://www.amazon.c...0?ie=UTF8&psc=1

 

4. On/off switch: https://www.amazon.c...0?ie=UTF8&psc=1

 

5. "The photo makes it look like the LED is in the film canister cap, over an inch from the screen, on the tail end away from the optics so the LED light passes through the screen."  Yes, the LED is in the canister cap (the LED wires are under the electrical tape) and rather close to the small hole in the center of the cap that you look through. You can see the LED bulb on the inside of the cap in one of the pictures. This puts the bulb close to the Ronchi grating when the gray cap is placed back on the black cannister.

 

If I still had my set-up I would give it to you, but I already gave it away to someone else who wanted to do DPAC.

 

Bob

[Optics Patent]

Perfect!  (Now, what's a "film canister"? )

[DAVIDG]

 A film canister  is what a roll of 35mm film was/is sold in, they happen to be 1.25" in OD.  You cut about 1/2" diameter hole in top  of the film canister and place the Ronchi screen in the cap.  The screen is placed in the cap so the lines on the screen are facing inward. The cap is then snapped back onto the canister. The bottom of the canister is cut open.  The LED is glued to the  screen just slight ly off center ie within a 1/8" to 1/16". The end of LED is filed flat so you have a flat surface to glue it down too the screen with some super glue. I would use a mini LED over the stand  size ones since they are smaller and you can get them closer to the center. Bend the leads of the LED over so they won't poke you in the eye and attach wires,  a battery case, dropping resistor and switch. So now you have made Ronchi eyepiece and light source for Double pass testing.  Here is a picture of mine.

   You first aim the scope at the optical flat without an eyepiece in it. The distance doesn't matter but it best to have the flat about  a foot or two  in front of the scope to reduce the air path between them. You then look down in the focuser of the scope.  You'll see your eye looking back at you. You adjust the scope so your looking right back into your eye. Now the scope is aligned to the flat. Place the Ronchi eyepiece into the scope and turn on the LED.  You look into the Ronchi  eyepiece and you  should see a pattern of lines.  If not rotate the eyepiece until you see the pattern. Focus the scope so you see three or four lines. The shape of the lines tells you the optical correction. True 1/10 wave or better optics will show dead straight lines when you have only three showing.  Focus the scope from one side of focus to the other ie the lines will get fewer  and  farther apart as you approach focus and then as you pass through focus you'll see more and they will be closer together. Watch the shape of them as you go from one side of focus to the other. If your optics are good they will stay dead straight, if you see any bowing or deviation from straightness that is an optical error. Move pretty quickly from one side of focus to other and look for any slight wiggle in the lines since they can look straight when they are stationary but you can detect a small amount of departure from straightness when they are moving more easily.  

   What is happening is light is first passing through the Ronchi grating making a slit light source., then through the telescope backwards. In theory perfect optics will make  perfectly  parallel light, any optical errors will distort that wavefront. The wavefront from the telescope is reflected off the optical flat and back into the telescope were the errors are again added in, hence doubling them and making them easier to see. That wavefront now passes through the Ronchi grating and will distort the shape of the lines. If no distorting you have a perfectly spherical wavefront ie all the light is coming to a perfect focus and the  lines will show no distortion as well. 

  As long as the optical flat is optically smooth it can many waves from flat and add very little error to the results. Also the distance of the telescope from the flat makes no difference and the error from the optics are doubled So what you have is a very sensitive test with very few sources of error. The result is high confidence in the test results. 

 

                     - Dave 

   

Edited by DAVIDG, 07 March 2019 - 04:30 PM.

[Optics Patent]

From this I assume that the Ronchi screen functions only when it is brightly and diffusely backlit by the LED.  That creates the bright ruled light source area (aka "Stripy Spot" to be reflected).  the rest of the screen has no optical effect.  Right?

 

The observer/imager is adjacent to the "stripy spot".

 

The LED is glued so its limb is right at the center of the cap, so the viewer's pupil can be similarly adjacent to the axis.

 

My next hope is that this can be simplified by putting the mirror immediately in front of the corrector, in the form of a full aperture solar filter.  I trust that secondary reflections off the rear filter surface are not going to interfere with the main imaged reflection of the screen.

I've ordered everything, and hope you let me know if I have misunderstood anything.

Thanks for the tutorial!

[DAVIDG]

The LED is glued slightly off center and you view thru the center,  which is the on axis image.   The image comes back thru the telescope then passes through the Ronchi screen again so only that area of the Ronchi  screen has  an optical effect, it is telling you the error in the system. 

  The full aperture solar filter may work but it has to be independent of the scope so you can get it correctly aligned to reflect the image back into the scope.  If you  screw the filter on it might not work because the filter maybe at slight angle. Also you need use the reflective side of the filter. Even thou Questar states the filter is optically very good, that is in transmission. So you can have a wavy piece of the glass that is uniformly wavy  on both side and it can transmit a very good wave front but have poor reflective wave front. So results from using  filter should checked against a know good optical flat to be sure the results match.

 

                 - Dave 

[Optics Patent]

Sounds like I was wrong in assuming that only the LED needs to be covered by the Ronchi screen.  I don't yet understand why, but you're saying I'm viewing through the Screen.  Is that necessary or just practical for assembly?

 

I understand that I'd need to rely on hitting the perfect alignment with the thread-on filter being perpendicular to the optical axis.  I'll cross my fingers that Questar's filter ($495 for the clear one) won't just be locally parallel but an adequate optical flat.

[DAVIDG]

 Here is a drawing of how you set up double pass to test an objective lens but the setup is the same for a Questar as well. Like I said the light first passes through  the screen to form a slit image then through the telescope, off the flat, back through the telescope and through the Ronchi screen again and your looking through the screen.

 

                   

 

 

 Here is  a picture of how you set it up to test a Newtonian. 

 

 

 This is similar to what you'll see when testing a Questar but hopefully much better. These are the results for  a  Celestron 5 with optics that are not that good. Note the lines are not dead straight. 

 

 

 - Dave 

Edited by DAVIDG, 08 March 2019 - 11:29 AM.