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Questar logo from 1990's (27,482 bytes)


Questar FR-1 MKIII Long Distance Microscope (81,183 bytes) The Questar FR-1 is a high resolution long distance microscope that differs from other Questar LDM’s in that it’s range of focus spans not only from near but also out to infinity. The FR-1 provides a working distance to the object of study from as close as 91cm (36 inches) and to as far away as infinity and so this instrument is suitable for imaging from it’s near focus limit out to the Moon and beyond. This allows the FR-1 to be employed at greater distances from the subject of study all the way out to infinity as an ultra telephoto lens with a diffraction limited field at prime focus 18mm diameter at the focal plane or even larger with the use of auxiliary lens elements. The optical resolution capabilities can reveal detail as fine as 6 microns at the closest working distance.

Right: FR-1 MKIII long distance microscope, with lens cover set to the side (81,183 bytes).
Click on image to see enlarged view (167,166 bytes).

The FR-1 MKIII are among the 33000 Series long distance microscopes. These are comparatively lightweight instruments and offer superb performance and at reasonable cost for general industrial or research applications, or for teaching. The FR-1 MKIII assembly includes one Axial Port (rear port) so it is compatible with common industrial CCD and video format cameras as well as with the popular 35mm film SLR or digital (DSLR) cameras. The FR-1 MKIII differs from the QM-1 MKIII and QM-100 MKIII instruments arrangements in that those instruments also incorporate a second port that is typically used for visual work with an eyepiece or for Brightfield illumination technique with a fiber optic light guide. It would be possible to configure the FR-1 MKIII Axial Port to support a camera, or it could accommodate an eyepiece or an eyepiece with a diagonal for visual applications.

Our long distance microscopes can accept auxiliary lenses that permit the user to increase or decrease the field of view, these thread into the provided Camera Coupling set. The changes in field of view will depend on comparative formats to be employed, as well as the lenses. So for example if you are employing a 2/3 inch (8.8 mm) format sensor then you could increase the field of view by changing this for a larger format digital SLR for example. Alternatively you could increase the field of view by employing the 2/3 inch sensor with a Positive Lens, these are available in focal lengths of 100 mm, 130 mm, and 172 mm. To increase magnification you can attach a Barlow Lens.

The standard Questar FR-1 MKIII (PN 33004) is a catadioptric optical arrangement that incorporates a borosilicate corrector lens and auxiliary optics making this set suitable for work from 350 nm in the ultraviolet up to 2200 nm in the infrared. For clients requiring added capabilities beyond that of the standard instrument we also offer a Fused Silica configured set (PN 33024) expanding the transmission Range from 180 nm in the vacuum UV up to 4000 nm, or Calcium Fluoride (PN 33044) with a working transmission range from 350 nm to keeping into the IR at 7000 nm.

Questar FR-1 MKIII Long Mount Long Distance Microscope (86,642 bytes)

Right: Current production FR-1 MKIII Long Distance Microscope, Long Mount variant with lens cover aside (114,018 bytes).
Click on image to see enlarged view (256,982 bytes).

The MKIII housing provides improved foresight alignment over traditional basic models. This configuration also allows for the factory installation of options including motorization of the focus control; with motorized focus control one can adjust focus with the push-button controller or even remotely.

These instruments are provided with a selection of tapped and threaded holes so that the instrument may be supported on steady fixtures or built into another device, or the instrument may be installed onto any of Questar's line of fixturing and transit/measurement positioning stages.


Optical Characteristics:

  • Design: Maksutov-Cassegrain Catadioptric
  • Standard Corrector Lens: BK7, MgF2 AR Coated; multilayer dielectric coatings optional
  • Optional Corrector Lens: Fused Silica (for enhanced UV spectral response), MgF2 AR Coated
  • Optional Corrector Lens: Calcium Fluoride (for enhanced IR spectral response), MgF2 AR Coated
  • Primary Mirror: Pyrex substrate, aluminum coated with SiO overcoat; Zerodur substrate optional
  • Primary Mirror Diameter: 96mm (3.78 inches)
  • Corrector Lens Clear Aperture: 89mm (3.5 inches)
  • Standard Secondary Mirror: aluminum coated with SiO overcoat; silver with ThF4 overcoat optional
  • Baffling: Helix in central tube, all interior surfaces black anti-reflection coated

Mechanical Characteristics:

  • Barrel Material: Aluminum hollow bar, machined from seamless stock.
  • Barrel Length: 24.8cm (10 inches)
  • Control Box: Cast aluminum, 24S-T4, corrosion resistant; selectable axial or 90 degree Port.
  • Internal Barlow Lens: 1.5x selectable for 90 degree port, flick knob controlled
  • Internal Prism: standard, flick knob controlled
  • Tube Assembly Length: 32cm (12.59 inches) front cell to focus knob
  • Tube Assembly Diameter: 10.7cm (4.23 inches) maximum overall
  • Tube Assembly Height: 16.5cm (6.5 inches) base of mount to top of eyepiece
  • Mount: Full length base of machined aluminum, 1/4"-20 and 3/8"-16 mounting holes
  • Focus Mechanism: Mirror thimble integral with stainless steel (s.s.) sliding tube.
    Slides on fixed stainless steel light baffle tub (centerless ground). Conical s.s. spring loaded.
    Focus rod 303, precision ground, 24 TPI; integrated inside control box
  • Finish: Aluminum components anodized natural, dark blue, or black
  • Carrying Case: ATA, Furnished Standard


  • Focus Range: 91cm (36 inches) to infinity
  • Optical Resolution: 6 microns at 91cm (36 inches)
  • Format: Diffraction Limited Field 18mm diameter
  • Distortion: 1 part in 15,000 edge to edge
  • Back Focus Distance: 70mm (2.75 inches) minimum measured from back plate
  • Field of View (2/3" format): 0.9mm (0.035 inches) to 15mm (0.59 inches)
  • Standard spectral response: 330nm to 2.2 microns, optional systems with wider spectral response available.
  • Optional extended Ultraviolet or Infrared imaging response: from below 200 nm or up to 7 microns
  • Optional EXFO X-Cite illumination sources and accessories, including the high stability X-Cite exacte system.
Questar FR-1 MKIII Long Distance
Microscope Drawing
Above: FR-1 MKIII Long Distance Microscope Dimensions (1,061 bytes)

Object Distance Numerical Aperture f/No.
91.4 cm (36 inches) 0.0396 12.6


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