Meade ACF 6″ is a Schmidt-Cassegrain mirror-lens telescope. The declared aperture is 152 mm (6 inches), focal length is 1524 mm, and the focal ratio is 1:10. The exclusive UHTC multilayer coating and mirror reflectivity of 95% are declared. The optical design features coma elimination (ACF technology – Advanced Coma Free) due to the use of an aspherical secondary mirror instead of a spherical one. This provides better image quality across the field. The telescope has not eliminated the field curvature, and it does not interfere with visual observations, but when shooting with a large APS-C sensor, a reducer-corrector (Meade ACF 0.68x or Optec Lepus ACF 0.62x) must be used.The tube came with a Meade LX85 mount.
The tube is supplied in a cardboard box. The kit includes an optical tube with a front protective cover, 26 mm and 9.7 mm eyepieces, a diagonal mirror, an 8×50 finder, a visual adapter, and a finder mounting platform. The finder’s alignment is adjusted using 6 screws. The crosshair in the finder is very thin. The finder mounting platform is non-standard.
Metal tube with a diameter of 177 mm. The length of the tube with a cover and focuser handle is 420 mm. The length from the cover to the thread is 390 mm. The weight of the tube with a cover and a visual back is 4.52 kg, with a finder – 5 kg. There is a sticker with quality control marks on the tube. A long dovetail mounting plate is screwed to the tube.
The focuser wheel is metal with ribbed knurling, length 57 mm, diameter 22 mm. The focusing of the tube is internal due to the movement of the main mirror. The focuser handle rotates tightly.
Thread at the exit of the tube with a diameter of 50.7 mm. The diameter of the hole in the “carrot” is 31.5 and 42.2 mm. Adjustment of the main mirror is not provided.
The measured aperture is 151 mm. The corrector coating is lilac color. The corrector plate is recessed by 18 mm. The diameter of the secondary mirror cell is 71 mm, the height of the secondary mirror frame is 18.5 mm. The internal Allen screws on the secondary mirror frame are adjusting. The external screws on the secondary mirror cell fix the secondary mirror on the corrector. A light-protective hood is attached to the mirror from the inside. The central obstruction for the measured aperture and frame diameter is 47% (!). There is an assumption that the Meade ACF 6 telescope uses a secondary mirror from the Meade ACF 8 telescope. An interesting fact is that the actual size of the reflective surface of the secondary mirror is slightly smaller than the physical size of the mirror due to a special ring.
There is a leak in the light shield – some light passes directly from the tube. This is visible when looking into the telescope’s outlet without a visual adapter and shifting the eye.
The central obscuration, measured from the secondary mirror shadow image, is about 46%.
Three-ray astigmatism was detected in star and artificial star testing. Star rays can also be seen in long exposure images.
To fix the astigmatism, it was necessary to slightly loosen three screws on the outer part of the secondary mirror cell. After this procedure, the astigmatism completely disappeared.
The tube is quite massive, the Sky-Watcher AZ-GTi mount in alt-azimuth mode pulls the tube to the limit, I do not recommend using this bundle. On the complete Meade LX85 mount the tube holds securely.
When visually observing the Moon and planets, the image is sharp. At high magnification, diffraction rings are visible around the stars without traces of astigmatism. However, the increased central obstruction worsens the contrast when observing planets, and when shooting, it increases diffraction effects.
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– Antares f6.3 reducer
– ZWO IR-cut filter
– ASI ZWO 183MC camera.
Stacking 100 frames from 2657.
An example of a picture before astigmatism is corrected, rays are visible on Jupiter’s satellites:
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
800 frames from 4532.
After astigmatism fix:
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
800 frames from 4528.
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
800 frames from 4221.
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
800 frames from of 2981.
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
800 frames from 4531.
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
Composition of 1000 frames from 45262.
Equipment:
– MEADE LX85 6″ f/10 ACF telescope
– NPZ 2x Barlow lens
– ZWO ADC atmospheric dispersion corrector
– QHY IR-cut filter
– QHY5III462C camera.
1000 frames from 30177.
SUMMARY
+good image quality on the axis and across the field
+compact size
-increased central obstruction
-compression of the corrector by the secondary mirror frame (fix possible).
Due to the large central obscuration (47%), the Meade ACF 6 is not the best choice for observing planets due to reduced contrast, but the image sharpness will be good. When shooting planets, the lack of contrast can be eliminated by processing, although the image detail will be at the level of Schmidt-Cassegrain with an aperture of 127 mm and a central obscuration of 38%. The tube is well suited for observing and shooting deep-sky objects and the Moon due to the corrected field. When shooting deep-sky objects, it is advisable to use the native reducer to increase the aperture and level the field.