Questar Tips and Tricks

A lifetime is not long enough to exhaust the possibilities on using a Questar. A classic does not age, it just evolves. Over the 50 years of existance, the Questar looks very similar to its 1954 entry version. What instrument today can rival that and still be held in such high esteem and demand?

Questar is a multi-dimensional instrument, and for those mystics that like to exist on many thought planes, its the likely choice. All around us is change, from the smallest creatures to the expanding universe. Questar provides a gateway to tap into that cosmic energy surrounding us.

Hacking the Axial Port

On my 1979 Duplex Questar, the axial port was measured as 30mm x .75 (or 1-3/16-32 tpi). Older Questars have a smaller .925-32 tpi axial hole. In order to expand Questar to take popular refractor and Schmidt Cassegrain Telescope (SCT) accessories, a Hutech 36.4mm adapter #7316 was modified by turning the un-threaded end down to 29.4mm and then threading the end to a .75mm pitch. The suitability of this thread can be verified by using the 30mm eyepiece adapter ring as a nut (note: this applies only if you have the Questar swivel camera coupling accessory). This adapter will allow the use of a Hutech Helical Focuser (#7315) for fixed focal length focusing with a digital or video camera. It also allows using the 36.4mm Large Accessory Ring (LAR), which converts the Questar to take the 2 inch -24 tpi SCT threaded accessories (e.g. visual back, focal reducer). The table below illustrates several hookups and image results with these modifications. These results show that the focal reducer provides increased field at minimum zoom levels, and brighter images. Preliminary calculations show that a 33 percent gain in system speed can be obtained using the .63 focal reducer with the 40mm Williams Optics 4337 ocular. Although primarily designed for digital camera's with faster and larger lenses (e.g. Olympus), results show that the 4337 works well with the Nikon 4500 at lower zoom levels. And that is the point of this exercise; to get suitable field at lower zoom settings.

Hutech 36.4mm to 1.25 inch adapter, with and without thread modification The test setup with the Nikon Coolpix 4500 is shown below. Because of the small 1.5" LCD screen, focusing was facilitated by using a 5 inch Sony Playstation One LCD monitor (note: This monitor has since been replaced by the superior Marshall VLCD4-Pro monitor). The shutter was controlled by the Nikon MC-EU1 remote control. The WO 40mm lens was adapted using a 28mm to 37mm step ring. The dime in the center of the target subtends an arc of about 10 minutes at 45 feet. This is same size of Messier M13, so this provides a good scale comparison.
Nikon 4500 afocal with celestron .63 focal reducer and WO 4337 40mm EP

Afocal Vignetting with a Digital Camera

Hutech Helical Focuser installed for digital photography, with Williams Optics (WO) 40mm EP LAR 36.4mm installed with Celestron SCT f/6.3 focal reducer
Olympus C2000 attached afocal to Hutech focuser with WO 40mm EP. Nikon CP4500 attached afocal to Celestron Visual Back with WO DCL-28 (24mm) EP.
Target at 45 feet.  Dime subtends arc of .1592 degrees.  Min zoom of 37mm (35mm equiv), 1/80 sec, ISO 200, C2000 photo with WO 40mm EP. Olympus C2000 photo.  Target at 45 feet, WO 40mm EP, max zoom (106mm ), ISO 200, 1/40 sec.
C2000 photo with WO 40mm EP.  Target at 45 feet.  Min zoom at 37mm  (6.5mm actual) with Celestron .63 focal reducer, ISO 100, 1/125 sec. C2000 photo with WO 40mm EP.  Target at 45 feet.  Max zoom at 106mm (19.5mm actual) with Celestron .63 focal reducer, ISO 100, 1/10 sec.
Nikon CP4500 photo with WO 40mm EP.  Target at 45 feet.  Zoom at 1.75x  with Celestron .63 focal reducer, 1/8 sec, f/3.2. CP4500 photo with WO 40mm EP.  Target at 45 feet.  Max 4x zoom  (32 mm actual) with Celestron .63 focal reducer, 1/4 sec, f/5.1.
CP4500 photo with WO 40mm EP.  Target at 45 feet.  Zoom at 1.75x  (14mm actual), 1/15 sec, f/3.2. CP4500 photo with William Optics 40mm EP.  Target at 45 feet.  Zoom at 4x  (32mm actual), f/5.1, 1/8 sec.

Balance Issues

The Questar was designed with portability in mind. So a good rule of thumb, is to choose attaching accessories accordingly. Any heavyweight camera or eyepiece can cause balance problems. For proper balance, the telescope tube should be in equilibrium when the declination lock knob is fully loosened. PVC coupler used as a counterweight on end of Questar  dewcap, lined with black flock paper When one adds a camera, the balance is upset, so one must compensate by adding weight to the opposite side of the fulcrum. A counterweight can be purchased from Questar Corporation or you can easily make your own from PVC plumbing fixtures. The photo shows a 4 x 4 coupler that will slip directly over the end of the dewcap without modification (after being lined with black craft velvet or flock paper). A 3/8 - 16 bolt can be used to add appropiate ballast weights. In order to prevent the dew cap from shifting when in equatorial, a wide rubber band placed around the dew tube will provide sufficient friction to anchor in place. The following steps can be used for construction:

  1. Spray inside of PVC coupler flat black.
  2. Modify a 3/8 - 16 NC T-Nut by grinding off the four prongs.
  3. Drill a 13mm hole on the five inch diameter edge of the coupler. Insert the T-nut tube end in the drilled hole and epoxy in place.
  4. Attach black flocking inside of the four inch I.D. side of coupler.

Axial Eyepiece Adapter

Starting with two inch diameter by two inch length of Delrin rod, an eyepiece adapter was made using a 7 x 10 mini-lathe. Delrin has excellent machineability; being also one of the most durable and strongest of plastics. The adapter takes from 2 to 4 hours to make; depending on your lathe skills. All work was done on the lathe, except for drilling of the #7 hole for the 1/4-20 tapped hole. The collar end was left two inches diameter and has a .380 inch wall to contain the eyepiece retaining screw (note: EPs can vary from the nominal 1.25 inch specified).  EP adapter being threaded, by turning to 29.70mm diameter, then threading .75mm pitch The total length of the adapter is 2-3/8 inches. This length is arbitary and could be made less than two inches if desired. Since Delrin Rod is already a dull black color, there is no need to anodize or paint (as when using aluminum or PVC). The cost Finished adapter for Questar axial opening of base materials is about two dollars; a far cry from $60 a commercial adapter would likely cost! The axial adapter has a very good application for use with digital cameras using the afocal method. When using the wide-field eyepieces designed for afocal hookups, the eyepiece adapter will allow closer coupling to Questar's optics; providing an optically faster system with less vignetting.

When Braymer was at the helm of Questar, there was no way he could have envisioned the plethora of imaging possibilites available today. The silver based photographic solution is on borrowed time, as digital imaging rises to take its place. For Questar, this is a good thing. The CCD has the sensitivity to record the rapier-like images provided by Questar optics; many orders of magnitude greater than film photography. And the lighter packaging of the digital imagers, means the Questar is not burdened by the weight of these behemoths. So Questar Corp. has provided an accessory called a Slip Fit Extension Tube (same function as Axial Eyepiece Adapter above) that aids in attaching these digital devices, and provides an alternate means of using third party 1-1/4 inch accessories. The tube has a 31.7mm ID, and is 45.5mm long, with a 37mm OD. The retaining screw is a bit small, so I enlarged the hole with a 7/64" drill (or #36 drill), and tapped the hole to 6-32 thread. The metal screw was replaced with a non-marring nylon 6-32 screw.

Some typical uses of these devices include afocal photography with digital cameras and camcorders, and surveillance camera imaging, as shown below. Visual users will benefit by easier terrestrial viewing of landscapes, and the availability of a plethora of third party accessories available in the 1-1/4 inch format.

Axial Port Applications
Axial port adapter's for 1.25 inch accessories. Homebrew adapter on the left. Nikon 4500 afocally attached to Questar axial port using Scopetronix WA eyepiece. Video camera coupled to axial port with C to 1.25 inch adapter.

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