AGO iDK Optical Design

AGO Imaging Dall Kirkham astrographs are designed and built to be no-compromise astroimaging platforms.  With outstanding wide-field correction, AGO iDK astrographs will meet the needs of the most demanding astroimager.

Optical Design

AGO conducted extensive modeling and optimization to create a Dall Kirkham design that produces 6 micron (and smaller) RMS spots sizes to the corner of CCD chips as large as those found in cameras such as the SBIG STX 16803.  The field of CCD imaging is constantly evolving and AGO designed our iDK line to integrate seemlessly with the current state-of-the-art in CCD equipment as well as the next generation of equipment.

Traditional Dall Kirkham telescopes have a well-deserved reputation for excellent on-axis performance.  Off-axis, however, the traditional Dall Kirkham design suffers from significant image abberations that have greatly restricted its use as a deep sky astrograph.  AGO iDK telescopes use a two element corrector that reduces coma, astigmatism, and field curvature to negligible levels and makes the AGO iDK astrograph line capable of the highest levels of imaging performance.  The optical corrector uses high grade, broadband anti-reflection coated optical glass elements in a permanently aligned fixture.

With star sizes under 6 micron RMS in diameter at 26mm off axis, AGO iDK astrographs offer outstanding performance that ensures that the telescope is not the limiting factor when it comes to high-resolution imaging.

Below are full field polychromatic spot diagrams and RMS spot vs field diagrams for the AGO 12.5" f6.7 and 16" F6.7 iDK telescopes.  No field curvature was added so what you see is what will be produced on the flat plane of the CCD chip. Click on each image of a high resolution view.

 

AGO 12.5" iDK Full Field Spot Diagram for a SBIG STX 16803 chip (Airy disk reference circles)

 

  

AGO 12.5" iDK RMS Spot Radius out to corner of SBIG STX 16803 size chip

 

AGO 16" iDK Full Field Spot Diagram for a SBIG STX 16803 chip (Airy disk reference circles)

 

  

AGO 16" iDK RMS Spot Radius out to corner of SBIG STX 16803 size chip

The AGO iDK optical design uses easy to manufacture spherical surfaces on all of the optics with the exception of the primary mirrors which have ellipsoidal surfaces.  Although the name doesn't exactly roll off the tongue, elllipsoidal mirrors have less correction than Newtonian parabolic mirrors and Ritchey Chretien hyperbolic mirrors thereby reducing the cost, complexity and time required to manufacture them.

Back Focus

Back focus is a precious asset when it comes to CCD imaging and all AGO iDK astrographs provide a generous 11" of back focus to accommodate even the longest imaging trains.  A variety  of 3.5" extension tubes are available to very rigidly secure your camera in position.

Baffling, Stray Light, and Vignetting

AGO iDK astrographs have primary and secondary baffles that eliminate any chance of unwanted light directly falling upon the CCD chip.  Each baffle is conical in shape to minimize vignetting and is constructed from very strong yet very lightweight carbon fiber composite.

The tube of each AGO telescope is completely lined with a pitch black, synthetic flocking paper that is permanently adhered to the wall using an epoxy adhesive.  This flocking paper noticeably darkens the interior of AGO telescopes and helps ensure that very high contrast images are produced at the image plane.

Finally, AGO iDK astrographs have been designed to provide clear apertures sufficient to provide excellent off-axis illumination at the image plane.   With larger diameter chips becoming more common and with larger adaptive optics devices on the horizon, rest assured that AGO iDK astrographs will maximize the potential of your CCD equipment by providing excellent wide-field performance.