ASKAR REFRACTOR SQA85 PETZVAL

ASKAR REFRACTOR SQA85 PETZVAL

Technical Specifications

• Aperture 85 mm
• Focal length 408 mm
• Focal ratio f/4.8
• Petzval quintuplet optical design with integrated corrector
• Full-frame 44 mm image circle without backfocus calculation
• SD glass lenses including two elements for advanced chromatic correction
• Central star point RMS below 1.6 µm
• Edge star point RMS below 2.5 µm
• Retractable dew shield
• Integrated tube rings with manual locking screws
• Six M4 and M6 mounting points for accessories and dual OTA installation
• Multifunction finder base integrated into the handle
• 290 mm Vixen-type dovetail plate
• Suitable for astrophotography and standard photography with DSLR and mirrorless cameras
• High-precision 360-degree rotator with engraved scale
• Rigid CNC-machined 2.8-inch dual-speed focuser
• Focuser with internal anti-reflective treatment
• Rear photographic adapters M48, M54 and M68 included
• Optional 85 mm handle
• Optional 20 mm riser

Superior star point performance
Quintuplet air-spaced lens design, including 2 pieces of SD glass.
The central star point has an RMS radius of less than 1.6 µm, and the corner star point is less than 2.5 µm, showing a super-fine star point.
It also has excellent full-field illumination and MTF data.

Petzval Structure
Integrated self-flattened design, supporting a 44 mm full-frame image circle, with no need for additional flatteners and no need for further calculation of back focus.
Between 40 mm and 70 mm connection distance, users can directly use it for shooting once the OTA is focused.

Retractable dew shield

The dew shield is designed to be retractable and can be deployed when needed.
It protects the lens from the impact of external and internal light while preserving the optics itself.

Integrated tube ring

Enlarged hand screws allow opening and closing the tube ring without additional tools.

The ring includes six M4 and M6 threaded holes on each side, making it easy to install a base or dovetail plate and attach various accessories.
It is even possible to mount a second optical tube for imaging.

The assembly consists of an integrated pair of tube rings with a hollow structure in the center to reduce total weight.

The handle located on top of the tube ring is equipped with a multifunction finder base for installing astronomical accessories.

Finder bases

On both sides of the focuser, there are two finder bases, eliminating the need for disassembly when changing finder positions.
They also provide additional attachment points for other astronomical accessories.

Dovetail plate

Standard 290 mm Vixen-style dovetail plate, easy to install and remove.

Diversified photography applications

In addition to connecting to an astronomical camera for astrophotography, the SQA85 can also be connected to a mirrorless or DSLR camera for regular shooting.

360° rotator

The rear of the focuser is equipped with a 360° high-precision rotator with a graduated scale, allowing the user to adjust and save the rotation angle.
It also features an enlarged locking screw for easy securing, even under heavy load.

Large rigid dual-speed focuser

Dual-speed 2.8-inch rigid rack-and-pinion focuser, compatible with most motorized focusers on the market.
The focusing travel is 32 mm, and the focuser tube is engraved with high-precision markings.
The entire focuser barrel is CNC machined with an anti-reflective interior design and matte paint, providing extra protection against stray light.

Rear-end adapters

The rear of the SQA85 is equipped with multiple adapters, all toothed and ribbed for easy manual rotation without slipping.
Adapters are available in M68, M54 and M48 sizes and can be used to attach various accessories, such as full-frame cameras.

High-quality machining

The entire SQA85 tube is made using high-quality CNC machining with anodized and surface spray-paint treatments.
The top handle and the focuser feature exclusive nameplates, demonstrating high-end finish quality.

All-metallic handle (optional)

An 85 mm all-metallic handle can be purchased separately for easier use.

Heightening section (optional)

A fully-metal 20 mm riser can be purchased separately.
It further reduces the risk of telescope collision during equatorial mount operation and creates more space under the OTA to accommodate different connection devices.

Optical path

The SQA85 features a quintuplet air-spaced optical design including 2 SD glass elements.

MTF curve

The modulation transfer function (MTF) is a quantitative description of image sharpness, including resolution and contrast of an optical lens.
The vertical axis represents MTF value, while the horizontal axis indicates the distance from image center to edge.

Across the two curves for high and low frequencies, even at full-frame edge, the sagittal deviations of the SQA85 remain very small.
At the low frequency of 10 LP/mm, the value stays above 0.9, demonstrating the high resolution and precision of the SQA85.

Relative illumination

Relative illumination (RI) represents combined light loss and attenuation at the edges of the lens. The RI curve illustrates illumination (%) variation across the sensor.

Illumination variations can affect the image.
The vertical axis shows illumination percentages, and the horizontal axis shows distance from the center to the frame edge.

The SQA85 ensures high illumination of about 85% even at full-frame edge, reducing vignetting.

Spot diagram

The imaging quality of the optical system can be evaluated by analyzing spot distribution on the spot diagram.
The SQA85 exhibits a central star point with an RMS radius of less than 1.6 µm, and a corner star point below 2.5 µm, demonstrating excellent star sharpness.

ZYGO objective chart

The ZYGO interferometer is internationally recognized as a reference instrument for testing optical lens quality, and SQA85 test results reveal excellent star-forming performance.

SQA85 electronic focuser assembly diagram