MundiScope equipment review
Askar 71F
A 71 mm flat-field refractor for a closer look at nebulae, clusters and larger galaxies.
By MundiScope · Updated · Specifications and calculated framing
In plain English
The 71F has the largest aperture and longest focal length of our three Askar models. With the same camera, a target appears about 20% larger across the image than with the 60F. Its four-element, flat-field design helps maintain focus across the sensor. More aperture offers greater light-gathering area, but it does not guarantee a sharper final image: seeing, focus, exposure and tracking still matter.
A good choice for
Targets that benefit from a tighter composition than the 60F, such as smaller nebulae, clusters and larger galaxies.
What to keep in mind
A longer focal length makes tracking, focus and atmospheric steadiness more noticeable. Very extended targets may need more than one frame.
How much sky fits in an image?
With the ZWO ASI533MC Pro camera, this configuration covers approximately 1.32° × 1.32°. That is about 2.6 full-Moon widths across the frame, using half a degree as a familiar reference.
Each pixel samples about 1.58 arcseconds of sky. These are calculations from focal length and sensor geometry, not measured image quality. Cropping, atmosphere, focus and tracking affect what your final image shows.
Compare fields of view →Detailed specifications, explained
Start with the overview, then open the technical details when you want to understand the camera and optics.
Optics, camera, tracking and image scale
- Aperture
- 71 mm
The diameter of the main lens or mirror. A larger aperture collects more light and can resolve finer detail under suitable conditions.
- Focal length
- 490 mm
With the same camera, a longer focal length gives a closer view of a smaller area of sky.
- Focal ratio
- f/6.9
Focal length divided by aperture. A lower number generally records extended objects more quickly with the same camera and comparable transmission.
- Optical design
- Quadruplet air-spaced flat-field APO
Refractors use lenses; a Newtonian uses mirrors. Field correction helps keep stars better shaped away from the centre.
- Central obstruction
- 0.0% of aperture diameter
The secondary mirror blocks some light in a reflector. This percentage is a diameter ratio, not a percentage of light lost.
- Corrected image circle
- 44 mm
The image area the optics are designed to cover. It is different from the field of sky captured by the fitted sensor.
- Focuser
- Rack and pinion · 50 mm travel · 10:1 fine adjustment
Focus brings stars to their smallest size. Remote adjustment depends on the equipment fitted at the site.
- Camera
- ZWO ASI533MC Pro
A colour astronomy camera. The figures below describe its native sensor, not a guaranteed download format or processed image size.
- Sensor
- Sony IMX533CQK-C · 11.31 × 11.31 mm
Sensor size and telescope focal length together determine how much sky fits in one frame.
- Native resolution
- 3008 × 3008 pixels
The camera's native pixel grid. Cropping, binning or processing may change a delivered image's dimensions.
- Pixel size
- 3.76 μm
The physical size of one sensor pixel. Together with focal length, it determines the angular sampling below.
- Calculated field of view
- 1.32° × 1.32°
Approximate uncropped field with this camera and optical configuration. It describes the frame, not which targets are currently visible.
- Calculated image scale
- 1.58 arcsec/pixel
How much sky each pixel samples. A smaller number does not guarantee sharper detail if the atmosphere or tracking blurs the image.
- Sensor readout
- 14-bit ADC · 50,000 e− nominal full well
Readout precision and charge capacity describe the sensor. Effective dynamic range varies with the gain setting.
- Read noise
- 1–3.8 e− (manufacturer range)
Electronic noise added during readout. The value depends on the operating gain; this is not a measurement of a specific session.
- Peak quantum efficiency
- >80%
The manufacturer's peak light-to-charge conversion figure. Sensitivity varies with wavelength; it is not total system transmission.
- Mount
- ZWO AM3 · equatorial configuration
Tracks the apparent motion of the sky. Guiding, alignment and conditions affect the result of longer exposures.
- Filters & rotation
- Check the session's available controls
A filter thread or manual rotator on an optical tube does not mean a motorised filter wheel or remote rotation is installed.
- Optical transmission
- Not specified
Total light throughput has not been established here. No exposure-time guarantee is inferred from aperture alone.
This is a guide based on published specifications and calculated framing, rather than a scored laboratory test. Session controls and equipment availability are shown when you connect. Sensor specifications do not guarantee a particular capture format or output resolution.