Alcor-System has optically designed, developed and manufactured a 4’’ field corrector for newton telescope (or for parabolic mirrors). It uses special glasses to get the best performance from 300 mm to 700 mm diameter telescope with low F/ (down to F/2.8). This corrector can offer a 36x36 mm corrected field to near diffraction limit. This is a good choice for camera with BSI Sony IMX sensor such as IMX455, IMX461 and IMX411.
Below is theoretical optical performance on 500mm F3.5 parabolic mirror (conic constant = -1). Almost diffraction limited performance is offered across the whole field of view ( 52 mm or 2° x 2° field of view). 400 to 700 nm wavelength has been considered.
On SKY image samples
This field corrector has been extensively tested on sky with a 500 mm F3 Newtonian telescope owned by Laurent Bernasconi. Below the result of SHO exposure with ASI 6200 MM ZWO camera. Please click on image to get full resolution.
Optical performance from this corrector is clearly demonstrated as very good. Optical alignement and distance from focal plane are critical. F3 optical tuning is important and might take several hours to be completed. PRISM software has a tool to achieve such alignement and to minimize field curvature.
FITS raw image samples can be provided on request for deeper inspection and assessment.
4 inches field corrector for Newtonian telescope
More simulation cases are visible in this PDF document (from 300 mm Newtonian to 700 mm F2.8) to assess field corrector performance on various optical setups. List of compliant focusers are also proposed into this document.
Currently prices are subject to variations, please ask us for price of this item
The mechanical drawing of the corrector is just below, and 157 mm long and diameter is 102.2 mm (4"). The focus offset is 12.3 mm. Focal length is slightly reduced by a factor of 0.5 to 0.75 %
Mechanical drawings
Optical performance
For customized optical simulations (optical setup or other wavelengths), please contact us.
The front attachement is made of 6 M3x10 metric screw on 96 mm diameter. To attach your camera please contact us for mechanical solutions. The weight of this item is 1.55 kg
Image above : the black ring is is the size of the airy disk of a star.
Image above : Vignetting plot from field center to 26 mm distance for 500mm F3.5. 20% loss is present, nevertheless unflat fielding image resolves the issue.
The image below is a special crop assembly from 9 areas from center and edges of the image above. Star shape is perfect, despite the 3 wavelength used (500, 656 and 672 nm)
The next image is also a crop assembly from a monochrome image with L filter, wavelengths from 380 nm to 700 nm.
The next plot shows the encircled energy for many fields for 500mm F3 telescope. This is very close to diffraction limit.
The front attachement is made of 6 M3x10 metric screw on 96 mm diameter. To attach your camera please contact us for mechanical solutions.
Finally, the next plot shows is the distorsion grid amplified. This is a pincushion type of 0.9% at the edge of 36x36 mm sensor. This represents 230 µm of optical shift at that location.
The actual anti-reflection coating plot of the lenses is visible below. It is optimized from 400nm to 900 nm