ASKAR REFRACTOR SQA55 PETZVAL

ASKAR REFRACTOR SQA55 PETZVAL

TECHNICAL DATA SHEET

• Aperture 55 mm
• Focal length 264 mm
• Adjustable focal ratio from f/4.8 to f/22
• Optical type: Petzval quintuplet astrograph
• Optical design: air-spaced lenses
• Optical elements: one SD glass element and one ED glass element
• Integrated Petzval field correction
• Central star point RMS radius below 2.5 µm
• Edge-of-field star point RMS radius below 4 µm
• Relative illumination of approximately 90 percent on full-frame sensors
• Full-frame sensor compatibility
• Graduated aperture ring with fixed reference marks
• Reversible lens hood with groove locking system
• Front filter thread M67
• Rear filter thread M48 with integrated 2-inch filter thread
• Usable connection distance between 50 mm and 60 mm
• Dual-speed focusing with independent coarse and fine adjustment
• Fine focus travel of ±1 mm
• Coarse focus with metric and imperial scales
• MXL gear on the focusing knob for motorization
• Locking screws on both fine and coarse focus adjustments
• Dual rotation system including a rotating optical tube and a 360-degree rear rotator
• High-precision rear rotator with engraved scale
• Four multifunction quick-release bases at the rear
• Compatibility with Askar SQA series accessories
• Tool-free conversion between astrograph and camera lens
• Quick-release handle with finder slot
• Bottom support with 1/4-inch and 3/8-inch threaded holes
• Vixen-standard dovetail plate
• Dovetail plate length 200 mm
• Manual quick-release system on the dovetail plate
• Suitable for astrophotography and everyday photography

QUINTUPLET AIR-SPACED SD GLASS PETZVAL ASTROGRAPH

PETZVAL LENS STRUCTURE

SUPER FINE STAR POINT

Quintuplet air-spaced optical design including 1 piece of SD glass and 1 piece of ED glass.
The central star point has an RMS radius of less than 2.5 µm, and the corner star point is less than 4 µm, showing extremely fine star rendering.

DESIGN SPÉCIAL ET RÉVERSIBLE DU PARE-SOLEIL

Le pare-soleil est fixé par une rainure. Lorsqu’il n’est pas utilisé, il peut être rangé à l’envers sur le tube afin de réduire l’encombrement, et lorsqu’il est nécessaire, il suffit de le remettre sur l’objectif.

① FILTER THREAD

At the rear of the OTA, it is equipped with an M48 adapter including a built-in 2" filter thread for direct connection of 2" filters.

② QUICK RELEASE BASE POSITION

Four multifunction quick-release bases are located at the rear of the optical tube. They allow mounting various accessories for photography and astrophotography and are perfectly matched with SQA-series accessories.

VARIABLE-APERTURE LENS

The aperture range goes from F22 to F4.8, with a graded adjustment ring and engraved scale on the tube to prevent accidental movement and preserve settings.

CAMERA QUICK-RELEASE BASE

Quick-release buttons located on the top handle and bottom bracket allow manual conversion of the OTA into a camera lens quickly and without tools

HANDLE

The handle includes a finder base slot for attaching various astronomical accessories.
It also features a quick-release design and can be removed without tools

BRACKET

The bottom bracket features 1/4" and 3/8" threaded holes for attaching a tripod.

DOVETAIL PLATE

The plate is a standard 200 mm Vixen-style dovetail.
Its underside includes manual tightening screws and a quick-release knob, allowing assembly and removal without tools.

M67 FILTER THREAD

The front of the lens includes an M67 filter thread for attaching photographic filters, convenient for daily photography.

DIVERSIFIED PHOTOGRAPHY APPLICATIONS

The optical and mechanical design is optimized for both astronomical photography and everyday shooting.
It can connect to astronomy cameras for star capture or to DSLR/mirrorless cameras to be used as a photographic lens.

DUAL-SPEED FOCUSER DESIGN

Fine and coarse adjustments can be made independently.

Fine adjustment includes a central indicator point, ±1 mm focusing travel, and a locking screw.

Coarse adjustment features a reference focusing scale with imperial and metric markings.
For daily photography, focusing can be referenced against this scale.
The coarse adjustment wheel has MXL-type timing teeth for use with a belt-driven electronic focuser.

For astrophotography, the coarse adjustment can be rotated to the infinity mark, with reserve travel beyond infinity thanks to the self-flattened Petzval field correction.

With a connection distance between 50 mm and 60 mm, users can directly shoot once the OTA is in focus, making accessory attachment easy.

Coarse adjustment also includes a locking screw for individual fine-tuning.

DUAL ROTATOR DESIGN

The optical tube and 360° rotator have independent locking screws.

For daily shooting, the whole assembly can be rotated.

For astrophotography, the high-precision rotator can rotate independently and is engraved with a scale for angle setting and memorization.

OPTICAL PATH

The SQA55 uses a quintuplet air-spaced lens design including 1 SD glass element and 1 ED glass element.

MTF CHART

The Modulation Transfer Function (MTF) quantitatively describes image clarity, including resolution and contrast.
The vertical axis represents MTF value and the horizontal axis the distance from image center to the edge.

Across curves for low and high frequencies, even at the full-frame edge, sagittal and tangential deviations remain very small.

At low frequency (10 LP/mm), the value stays above 0.9, demonstrating the SQA55’s high resolution and sharpness.

RELATIVE ILLUMINATION

Relative Illumination (RI) represents combined light loss and attenuation at the frame edges.
The RI curve shows illumination (%) variation across the sensor.

Variations affect the image, with the vertical axis indicating illumination percentage and the horizontal axis distance from center to edge.

The SQA55 ensures high illumination of about 90% even at the full-frame edge, minimizing vignetting.

ZYGO OBJECTIVE TEST CHART

The ZYGO interferometer is internationally recognized as a reference instrument for testing optical lens quality.
Test results of the SQA55 demonstrate excellent star-forming performance.

GRAPHIQUE DE TEST ZYGO

L’interféromètre ZYGO est reconnu internationalement comme un instrument de référence pour tester la qualité des lentilles optiques.
Les résultats de test du SQA55 montrent une excellente qualité de formation des étoiles.

SQA55 AFkit Electronic Focuser Assembly Diagram

① Dévisser la vis de blocage du réglage grossier.
Aligner l’échelle de la bague de réglage grossier avec la marque “infini”.
Aligner la rainure centrale du support moteur EAF avec la base, puis le fixer à l’aide des deux vis de blocage d’origine du moteur de mise au point électronique.

② L’utilisateur sélectionne les vis en fonction de l’équipement et fixe le moteur de mise au point électronique sur la platine de connexion standard, sans besoin de serrer complètement.