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How to Evaluate a Questar Telescope for Purchase

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#1 Optics Patent

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Posted 14 May 2018 - 01:19 PM

Whether one is buying in person, on Ebay, or though the classifieds, it’s important to know if the telescope is in proper working order before accepting it or sending it back.  Ebay auctions typically guarantee "fully operational and functions as intended."  Buyers should verify what is promised.  Unless deeply discounted as a repair project, buyers should explicitly confirm that the scope will be in full operating condition not requiring any factory service, and that any required factory service will be cause for return or price adjustment.  Also that all meaningful cosmetic issues are fully illustrated or described.

 

If you buy a Questar scope and don’t properly inspect it, you risk having a poor-performing scope that you’ll have a hard time selling for what you paid.

 

Exterior inspection.  This is usually not a cause for rejection, unless there are substantial cosmetic defects that were not disclosed and easily could have, such as a missing part on a side that isn’t illustrated.  Serious damage to the dew shield is sometimes a concern because the original colors are irreplaceable and can’t be repaired – same for vintage R.A. rings.  Missing badges on vintage scopes are also irreplaceable.  Paint scratches on control boxes and forks are common.  Small scratches and dings on polished metal is common, but major dents are not.  Make sure leg hole plugs are present, and legs properly install – slip fit legs will be snug and secure.

 

Slow motion drive operation.  This is the system that lets the user manually aim the scope by turning the two knobs.  The scope should move positively and evenly in all orientations without any slipping or rough resistance.  This requires lots of exercising to be sure that all portions of the drive discs are tested, including with the different parts of the pinions they may engage.  Under no circumstances should a knob and pinion turn without the disc turning.  This is easy to see on the declination axis and more challenging on the RA axis.  This is considered a normal wear item, and it’s not unexpected that a seller is unaware of some slipping that once it starts will only get worse.  The good news is that the factory will provide this service for about $100 per axis, complete.  They will also sell you the parts if you want to do it yourself in conjunction with a major restoration – this is a rare instance where doing it yourself saves you no money.

 

Slewing motion.  The scope should turn with respect to the base and fork.  The force should be reasonable and not overly stiff (enough to tip over a tripod) or loose (easy to knock off target with normal control inputs.  Note that it’s fine is the control knob spins when you slew, and also fine if both the knob and drive discs stay put.

 

AC drive.  When plugged in, this will make an audible buzzing sound.  Left in place, the fork with its RA indicator window and the RA ring will all rotate one revolution per sidereal day.  Put a tape mark on the base at one point, take a cell phone photo, and ensure on review that the RA ring has moved the number of hours since the photo was taken.  Again, the RA ring moves with the fork, so the indicator’s reading does not change with drive operation.  As a rule, these motors don’t become inaccurate, they simply fail to drive, and are easily replaced.  Note that when the arm is gently nudged clockwise and counterclockwise, there may be a little normal “click-click” play from the gear train backlash of a fraction of a degree.  The RA ring should move manually with your thumbs with respect to the base – hopefully clean without noticeable grittiness.

 

Eyepieces.  There are normally two included and should be clean or cleanable with a swab and lens cleaner – if anything but clarity remains after cleaning there are failed optics – nothing cleanable inside.  Since about 1970, Questar scopes have come with an adjustable “diopter adjuster” (eyepiece holder) that has an upper ring that focuses.  This may be stuck in one extreme position, with the seller confessing that “the finder doesn’t focus.”  This can usually be fixed with a pair of strap wrenches and replaced if not.  Tips for fixing here. Earlier models had fixed eyepiece holders with eyepieces that had internal focusing mechanisms.  Be sure you can remove the eyepiece holder from the control box.  It may be terribly stuck if someone had trouble with a stuck focusing ring.

 

Control box.  Each of the lever control should operate smoothly.  Avoid “flicking” the levers because it wears out the stops – control the motion.  Inspect the finder mirror beneath with a bright flashlight.  When cleaned (swab and lens solution) it should appear fully clear.  $25 to recoat if not.  Also inspect the finder lens with the eyepiece holder removed and Barlow shifted aside.  It should be clear.  Any haze or spiderwebs mean failed internal adhesive.  The upper face of the lens should not need cleaning, but a long swab may help.  Under bright light, the prism and Barlow should be clear.  That Barlow may have a finger smudge needing removal.

 

Finder.  The finder operates only with the levers in their “splayed” positions, not vertical.  Note that the levers may be misaligned, requiring a special non-Allen Bristol wrench to loosen and adjust.  When “in” toward each other they both should be vertical.  Adjust the eyepiece holder ring the get a comfortable focus.  The image should be clear, crisp and bright. 

 

Telescope focus.  Switching the right lever to vertical with give the telescope view.  Focus can be challenging at first.  There may be about 50 turns of the focus knob between extremes.  Distant objects with have the focuser “in” and close objects will have the focuser protruding out of the control box more than you might expect.  With the knob in all the way against the control box, you may have to unscrew it 10-15 turns to reach infinity.  It will turn easily along the entire range, and clear but light resistance will be felt at the outer limits of close focus (about 10 feet) and should not be forced.  One subtle focus issue associated with Questar telescopes is known as “focus shift.”  This causes the whole image to appear to shift when focus knob direction is changed.  A shift equivalent to a Jupiter diameter is normal.  Big noticeable shifts are not but can be adjusted with factory service.

 

Finder alignment.  This should be aligned with the center of the finder for distant objects, and for closer objects the telescope view will properly center 3” above the center of the finder view.  Slight misalignment is normal, but larger misalignments require readjustment, which is a simple process that can be done by the user. 

 

Optics coatings inspection.  With a bright flashlight, inspect the corrector lens and main mirror.  The corrector will show some dust and smudges under the intense light, but should have no haze or white texture.  Look for problems at the edge, and little snowflake like spots anywhere.  You will be able to tell whether issues are on the front surface or inside.  Don’t worry about a knuckle smudge and use a bulb blower to blow away dust.  The main mirror should be bright and free of any yellowing or bright white or silvery effects.  Inspect the very outer and inner edges especially carefully - even the thinnest line of silver-white at the edge can indicate the start of a problem.  Carefully observe the secondary reflector in the reflection in the mirror for any concerns.  Also note if the black paint inside the barrel shows scratches indicating careless service.  If the coatings are Broadband (BB in the serial number) then recoating is impossible and the defects must be lived with or the optics replaced at more than the cost of a used scope.  If conventional coatings, then the recoating cost is several hundred dollars if you are comfortable dismantling and shipping them, and much more for factory recoating.

 

Optics testing.  This is the most important test.  On a clear night with good seeing, a bright star overhead should generate a nice Airy disc image, possible with several faint concentric rings.  Any misshapenness that changes and squirms is an atmospheric issue, not a telescope problem.  Be sure the scope has settled at ambient temperature before making critical judgments.  To view the stability of the atmosphere you can focus closer (rod out, turn left) until you are focused on the air that might be turbulent from the heat of an object below.  With the star centered in the field of view, defocusing it in each direction should generate a round not oval blob.  If you see oval, be sure to double check that the star is centered.  Close to the focus, look at how the star defocuses.  If it focuses evenly that’s ideal.  If it elongates one way in one direction and perpendicular in the other, there is slight astigmatism in the system, and a concern if significant.   Note that perfect star images can be generated by failed coatings, which will cause lower contrast without hurting sharpness.

 

Solar filters.  Inspect any solar filter against the sun or a very bright light for more than a few minor pinholes.  Excess pinholes won’t create a safety problem but will generate foggy brightness in the image.  Using care, install any solar filter, and flip the finder solar filter to cover the finder objective and verify that you get a clear image without any vague fuzzy clouds or glow.  A weak finder filter doesn’t really matter since it’s used only for finding and not viewing, but it may be a point to justify a price adjustment.

 

For more information, one might also review the article on How to Sell a Questar, and simply ask in this forum.

 

Please add anything I have overlooked, and correct any errors I've made.


  • Matt Looby, davidmcgo, JHollJr and 1 other like this

#2 Paul Schroeder

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Posted 15 May 2018 - 06:27 PM

Hi Ben - 

 

Great article!  

 

There are two items I thought I'd suggest adding - I've run into both more than once on used Questars:

 

- Dewshield slippage - once extended, and with the scope pointed straight up, will the dewshield stay in place, or does it slip back down? If it doesn't stay in place, some kind of small intervention / repair is needed (usually this is pretty easy).

 

- Optical centering - I've seen at least two used Q 3.5s with de-centered optics.  This is manifested by the classic, concentric round star test pattern (when de-focused to six rings or so) not being located in the center of the field of view. IIRC in the two I saw, in the center of the field, an out of focus star was a pronounced skewed oval, but it turned into a proper circle close to the edge of field.  For most of us, addressing this requires a trip to Questar to fix.

 

Love following your Q7 restoration! You are a brave man smile.gif.

 

Paul


Edited by Paul Schroeder, 15 May 2018 - 06:35 PM.


#3 GR1973

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Posted 24 May 2018 - 02:43 PM

“Under bright light, the prism and Barlow should be clear”

Is is just a bright ambient light or strong flashlight?

Do we shine it directly on the prism or slanting tangential on it?

Thank you for these recommendations

All the best

#4 jag32

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Posted 25 May 2018 - 12:52 PM

 

 

Slewing motion.  The scope should turn with respect to the base and fork.  The force should be reasonable and not overly stiff (enough to tip over a tripod) or loose (easy to knock off target with normal control inputs.  Note that it’s fine is the control knob spins when you slew, and also fine if both the knob and drive discs stay put.

 

I have a question about this. The fine control knob does not spin on my 1965 Questar when I rotate the scope around the base.  There is no slippage and the fine control know does work perfectly, but when the base is rotated there is some modest friction and the fine control knob doesn't spin like the other axis which is buttery smooth. I called Questar and they said that this means one two things: the lubricant has dried up and the drive needs to be lubricated OR the drive itself has failed and needs to be replaced ($80).  Questar said that if there is no gap and and you can't see any light between the pinion and the disc, then tjis means the drive has likely failed and needs to be replaced and is not indicative of lack of grease. So I'm a bit concerned that the Questar I bought has a failed drive and should be rejected and returned to the seller.  $80 to replace the drive plus expensive shipping to and from Questar makes the deal I got no longer a good deal and I think I should reject my Questar. What do you think?



#5 jag32

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Posted 25 May 2018 - 12:54 PM

 

 

Slewing motion.  The scope should turn with respect to the base and fork.  The force should be reasonable and not overly stiff (enough to tip over a tripod) or loose (easy to knock off target with normal control inputs.  Note that it’s fine is the control knob spins when you slew, and also fine if both the knob and drive discs stay put.

 

I have a question about this. The fine control knob does not spin on my 1965 Questar when I rotate the scope around the base.  There is no slippage and the fine control know does work perfectly, but when the base is rotated there is some modest friction and the fine control knob doesn't spin like the other axis which is buttery smooth. I called Questar and they said that this means one two things: the lubricant has dried up and the drive needs to be lubricated OR the drive itself has failed and needs to be replaced ($80).  Questar said that if there is no gap and and you can't see any light between the pinion and the disc, then this means the drive has likely failed and needs to be replaced and is not indicative of lack of grease. So I'm a bit concerned that the Questar I bought has a failed drive and should be rejected and returned to the seller.  $80 to replace the drive plus expensive shipping to and from Questar makes the deal I got no longer a good deal and I think I should reject my Questar. What do you think?



#6 Optics Patent

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Posted 25 May 2018 - 01:23 PM

“Under bright light, the prism and Barlow should be clear”

Is is just a bright ambient light or strong flashlight?

Do we shine it directly on the prism or slanting tangential on it?

Try everything.  Understand that good optics can look bad (a little dusty or smeared) in the harshest light, and bad optics can look decent in forgiving light, including bright ambient.  There is no strict rule - trust your judgement.  Under bright LED flashlight lighting, good optics will look a little dirty, and bad optics will look, well, bad.

 

I have a question about this. The fine (R.A.) control knob does not spin on my 1965 Questar when I rotate the scope around the base.  There is no slippage and the fine control kno(b) does work perfectly, but when the base is rotated there is some modest friction and the fine control knob doesn't spin like the other axis which is buttery smooth. I called Questar and they said that this means one two things: the lubricant has dried up and the drive needs to be lubricated OR the drive itself has failed and needs to be replaced ($80).  Questar said that if there is no gap and and you can't see any light between the pinion and the disc, then tjis means the drive has likely failed and needs to be replaced and is not indicative of lack of grease. So I'm a bit concerned that the Questar I bought has a failed drive and should be rejected and returned to the seller.  $80 to replace the drive plus expensive shipping to and from Questar makes the deal I got no longer a good deal and I think I should reject my Questar. What do you think?

First, spinning is not important.  Healthy declination drives may or may not experience the knob "spin" behavior - either the drive discs and knobs will remain static as the barrel slews up or down, or the discs and knob will be engaged and the knob will spin.  The only bad behavior would be the the discs moving and the knob not spinning as if the pinion were engaged as if geared to the discs.

 

Second, in perhaps a dozen Q3.5 inspections, mostly my own including before and after service by me or the factory, I don't recall any ever having a spinning RA knob.  About half of good scope might have spinning Declination knob, and many of those only intermittently or on part of their range of motion.

 

I believe there may be a misunderstanding in your Q&A with the factory.  If as you say "the fine control kno(b) does work perfectly" then this is to spec.  There should be moderate additional friction to overcome to get it to slew.  Remember that's the friction it that "sticks" the fork to the drive gear-train.

 

I'm unaware of any lubricant ever being used between the disc edges and the pinion groove.  I do agree that if those disc edges are worn and bent inward they will extend farther into the groove, and you may see this intrusion in silhouette.

 

But the only test that matters - literally the only test - is whether the scope turns consistently, smoothly, and reliably as you turn each of the declination and RA knobs through the full range of motion.  From what you write, you have a perfect scope.

 

If you want, message me and we can set up a Facetime or Skype to look at this in detail.

 

I should also note that $80 is a good price for drive service (which I don't think you need) and one trick is to unscrew the six screws that hold the ring to the side brackets and send only the robust drive and not the delicate barrel.  (Third hand suggested to be sure things don't slip and scratch when unscrewed).



#7 GR1973

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Posted 25 May 2018 - 04:18 PM

Thank you optics patent

Regarding to LED flashlight do I shine it directly after removing the eyepiece because it’s difficult to shine it slanting?

Best regards

#8 Optics Patent

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Posted 25 May 2018 - 09:21 PM

Thank you optics patent

Regarding to LED flashlight do I shine it directly after removing the eyepiece because it’s difficult to shine it slanting?

Best regards

Shine it every which way you can.  There's no recipe, just the goal to discover problems.



#9 gplumfield

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Posted 15 February 2021 - 08:50 PM

 

 

If you buy a Questar scope and don’t properly inspect it, you risk having a poor-performing scope that you’ll have a hard time selling for what you paid.

 

Exterior inspection.  

 

Slow motion drive operation.  u the parts if you want to do it yourself in conjunction with a major restoration – this is a rare instance where doing it yourself saves you no money.

 

Slewing motion.  The scope should turn with respect to the base and fork.  The force should be reasonable and not overly stiff (enough to tip over a tripod) or loose (easy to knock off target with normal control inputs.  Note that it’s fine is the control knob spins when you slew, and also fine if both the knob and drive discs stay put.

 

 

Eyepieces.  

 

Control box.  

 

Finder.  

 

Telescope focus.  

 

Finder alignment.  

 

Optics coatings inspection.  

 

Optics testing.  .

 

Solar filters.  

Ben - another great article!  I'm going to pick up my new Q3.5 from Questar itself when ready (standard, quartz, PGIII) and I was hoping to give it a quick inspection to preclude having to return it if there is an issue, especially a mechanical one.  Is there a quick run through I could give it?  If I don't have something written down I'm afraid just its newness could blind me to any critical examination.  Thanks!

 

George



#10 alan.dang

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Posted 16 February 2021 - 10:33 AM

Exterior inspection is the big one. For the money, the mount surprisingly will not show up pristine and scratch free. It’s handmade and I suspect some of the team behind the assembly are older than their prime. It is not uncommon to see some scuff marks, irregular engraving, etc. On my DEC axis, the indicator is a V rather than a single line, and the lines of the V aren’t perfectly straight. There can be some casting errors and voids in the fork. Such is the nature of being hand made.

Just double check to see what scuff marks are there and that you are OK with them.

#11 Optics Patent

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Posted 16 February 2021 - 04:27 PM

I’ve never bought a new one but I have faith that Questar will make it right if there were a problem.

#12 gplumfield

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Posted 19 February 2021 - 07:54 PM

I've gotten so used to descriptions and pictures on here of folks' pristine Qs from the 70s, 80s etc. that it's a bit unnerving to think of a brand new one with any blemishes! But I guess I can understand about hand-made quirks, except that I'm coming from my AstroPhysics refractor and mount which were all hand-made (does CNC count as hand-made?) and as perfect as possible.

 

I'm hoping that my accepting and inspecting the telescope right there at Questar will insure a rejection-free example!




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