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.