Askar SQA55 55mm f/4.8 Quintuplet APO

The lens features a quintuplet air-spaced design, incorporating one piece of SD glass and one piece of ED glass. This design achieves an exceptionally fine star point, with a central RMS radius of less than 2.5 micrometers and a corner star point of less than 4 micrometers.

The design is self-flattening, eliminating the need to calculate specific back focus. The focal plan is between 50mm and 60mm calculated from the rear of the telescope, so users can immediately begin shooting once the OTA is focused.

The focusing mechanism features both fine and coarse adjustments, which can be controlled independently. The fine adjustment includes a central indicator point for precise control, offers a focusing travel of 1mm, and is secured with a locking screw. Conversely, the coarse adjustment is marked with a reference scale in both imperial and metric units, allowing for straightforward adjustments based on the scale during regular photography. Additionally, the coarse adjustment handwheel is fitted with MXL-type timing teeth, compatible with a timing belt for attaching an electronic focuser.

For astrophotography, users can simply rotate the coarse adjustment to the infinity mark to achieve focus, with extra leeway provided by the self-flattening design, which requires no specific back focus calculations within a 50mm to 60mm connection distance. This design simplifies the process of aligning the telescope with essential accessories and includes a locking screw for secure adjustments.

Quintuplet air-spaced lens design, including 1 piece of SD glass and 1 piece of ED glass. The central star point has an RMS radius of less than 2.5microns, and the star point at the corner is less than 4microns, showing a super fine star point.

Self-flattened design, no need to calculate specific backfocus between 50mm and 60mm connection distance, astrophotographers can directly use it for shooting after the OTA is in focus.

The lens hood is fixed by a slot, when the lens hood is not in use, it can be stored on the lens barrel in reverse to reduce the overall volume, and when using it, it only needs to be stuck on the lens.

The aperture range of the lens is from F22 to F/4.8, with a graded adjustment ring and a scale labeled on the lens tube to prevent accidental touching and save the adjustment parameters.

Camera quick-release knobs on the top handle and the bottom bracket, which can be used to convert the OTA to camera lens mode manually and quickly without additional tools.

The handle has a finder base slot, which can connect different astronomical accessories. The handle is a quick-release design and can be removed without additional tools.

The bottom bracket has 1/4 and 3/8 screw holes for attaching a tripod.

The dovetail plate is a standard Vixen-style 200mm dovetail plate. The bottom of the dovetail plate is designed with hand screws and a quick-release knob, which can be disassembled and assembled without addtional tools.

The front of the lens is designed with an M67 filter thread which can be connected to camera filters, convenient for daily photography.

Optical and mecahnical design optimized for both astronomical photography and dail photography. It can be used to connect to astronomy cameras to take star photos, or connect to DSLR/Mirrorless cameras to be used as camera lenses.

The lens tube and 360degrees rotator both have independent locking screws. For daily shooting, the whole body can be rotated. For astrophotography, the high-precision rotator can be rotated independently, while the rotator is engraved with a scale, which is convenient for adjusting and saving the angle.

The SQA55 is a quintuplet air-spaced lens design, including 1 piece of SD glass and 1 piece of ED glass.

The modulation transfer function (MTF) is a quantitative description of the clarity of the image (including resolution and 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 sets of curves corresponding to low and high frequencies, even at the edge of the full frame. The sagittal lines and sagittal lines distance of the SQA55 lens remain very small, and at the low frequency of 10LP/mm, it is higher than 0.8 overall, showing the high resolution and sharpness of the SQA55.

Relative illumination (RI) represents the combined effect of light loss and attenuation at the corners of the lens, and the RI curve illustrates the change in illuminance (%) accross 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 of the frame to the edge. The SQA55 guarantees a high illumination of about 90% even at the edge of the full frame, minimizing vignettings.

The imaging quality of the optical system can be evaluated by analyzing the distribution of the spots on the spot diagram. The SQA55 has a central star point with an RMS radius of less than 2.5 microns, and the star point at the corner is less than 4 microns, showing a fine star point.

The ZYGO interferometer is internationnally recognized as a more authoritative instrument for testing optical lens quality, and the SQA55 test results show great star quality.