Askar SQA85 - 85 mm f/4.8 Petzval APO Refractor - SQA85

The Askar SQA85 is a Petzval quintuplet refractor made with not one, but two SD glass elements for superb color, clarity and sharpness.  The SQA85 has a native focal length of 4.8 and a focal length of 408 mm, and it supports full frame cameras as well as APS.  Because of it's Petzval lens structure, which is beautifully flattened without the use of a separate component, there is no need to calculate a specific back focus.

About the SQA85 Optics...

The Petzval structure of the SQA85 offers an integrated self-flattened design with a 44 mm full frame image circle.  There is no need for additional flatteners and no need for additional calculation of the back focus.  With a connection distance of between 40 mm and 70 mm, users can simply focus the OTA and start shooting.

In the image above, note that the central star point has an RMS radius of less than 1.6 um, for a very small star point.  This quint also has excellent full-field illumination and MTF data.

Relative Illumination, or RI, represents the combined effect of light loss and attenuation at the corners of the lens, and the RI curve illustrates illumination changes (%) across the imaging range on the sensor.  Illumination variations can adversely affect the image. The vertical axis means different percentages of example illumination intensities, and the horizontal axis is the distance from the center to the frame edge.  The SQA guarantees a high illumination of about 85% even at the edge of the full frame, minimizing vignetting.

The modulation transfer function, or MTF, is a quantitive description of the clarity of the image, including resolution & contrast, of an optical lens.  The vertical axis is the MTF value, and the horizontal axis is the distance from the center of the frame to the edge.  In the two sets of curves corresponding to low and high frequencies, even at the edge of the full frame, the sagittal lines distance of the SQA85 lens remains very small.  At the low frequency of 10LP/mm, it is higher than 0.9 overall, showing the high resolution and sharpness of the SQA85.

The imaging quality of the optical system can be evaluated by analyzing the distribution of the spots on a spot diagram, shown below.  The SQA85 has a central star point with an RMS radius of less than 1.6um and the star point at the corner is less than 2.5um.

About the SQA85 Optical Tube...

The quality of the OTA starts with high quality CNC machining finished with anodized and surface spray paint treatments.  

A retractable dew shield protects the lens from damage and also keeps light from bouncing off of the optics, reducing contrast.

An integrated tube ring is super functional but lightweight due to its hollow design.  Large hand screws are easy to manipulate, even with gloves on, and you can open and close the ring without any additional tools.  There are 6 M4 and M6 threaded holes on both sides of the tube ring, allowing you to install the base or dovetail plate as well as any additional accessories.  Finally, a handle on the top of the tube ring is slotted and has a multifunctional finder base.

Speaking of finder bases, the Askar SQA85 has two of them installed on the focuser, one on each side, for the ultimate in flexibility.

Finally, a standard Vixen-style dovetail plate comes standard with this telescope, making it ready to attach to a variety of mounts.

2.8" Dual Speed R&P Focuser...

The dual-speed focuser used on the SQA85 is compatible with most motorized focusers on the market.  The focusing travel is 32 mm and the tube is engraved with high precision scales.  The entire focuser barrel is CNC machined and treated with anti-reflective matte paint inside to help eliminate stray light.  

The rear of the focuser is equipped with a 360-degree high precision rotator.  A precision scale allows the user to adjust the angle of rotation.  A big lock screw allows for easy locking even under high loads.

Last but not least, the SQA85 is equipped with a variety of adapters, all of which are toothed and ribbed to make it easy to rotate without slipping.  Included are M68, M54 and M48 adapters.

Specifications...

Aperture:  85mm

Focal Length:  408 mm

Focal Ratio:  f/4.8

Objective Lens:  Quintuplet Petzval APO

Total Length:  403mm with dew shield retracted, 439mm with dew shield extended

Format Specifications:  Full Frame

OTA Weight:  3.64kg

Weight Included Tube Ring/Dovetail:  4.62kg

Rear End Thread Type:  M48/M54/M68

Rear End Connection Distance:  Support 40mm - 70mm.  Recommend connection length is 55mm

Includes Case:  Yes