Daystar T-Mount Interference Corrector

Daystar T-Mount Interference Corrector

Photographers imaging with monochromatic light, such as hydrogen alpha, using an electronic sensor often find a wavy pattern of light and dark lines superimposed on their images. These lines are called interference fringes, interference patterns or Newton's rings. In long focal ratio applications, near-parallel light can reflect internally within the image sensor or camera, causing an addition or subtraction of light waves, resulting in the observed pattern.

The interference eliminator solves this problem by tilting the camera away from normal while keeping the center of the image sensor stationary, so that focus, framing and vignetting are not changed by tilting. Tilt changes the angle of incidence and optical path lengths within the image sensor, mitigating interference.

Installation and use:
Installation: The interference eliminator should be placed directly in front of the camera in the optical train. For proper operation, the distance from the male T-thread flange to the focal plane of the camera should be 55mm. On a DSLR camera with a T-ring, no spacers are needed, the T-ring sets the distance to 55 mm. On a CCD or Webcam camera, male to female T-ring spacers may be needed to bring the distance to 55 mm. If the distance is significantly different from 5 5 mm, the camera will move out of the crosshair and the focus position will change while adjusting the tilt setting of the interference eliminator.

Usage: Slightly loosen the thumbscrews and separate the two halves of the interference eliminator so that the camera tilts. Take a few images with the camera to check the interference pattern. Spread further apart if the pattern is still evident. Tilt it as little as possible to eliminate fringing - too far and you could lose focus at the top and bottom of the image, especially in fast focal ratio systems. If maximum tilt is reached without satisfactory effect, try full tilt in the opposite direction. In some severe cases, the interference pattern may not be completely eliminated, but will be reduced to the point where other techniques such as flat field or compositing may make the image acceptable.

Notes: On large sensors, such as those in 36x24mm full-format DSLR cameras, some vignetting may occur at full tilt due to the camera structure and the inner diameter of the T-thread. For an example of a full-frame Canon EOS 5D image at full tilt, click here. With 1.5-1.6x crop webcams or digital SLRs, vignetting will not occur.

General features:

♦ The center of the sensor remains fixed: no focus, framing and vignetting changes

t-thread connection

♦ Working distance 55 mm from the male T-thread flange to the focal plane

♦ No vignetting with APS size sensors even at full tilt

♦ Vignetting with full frame sensors only at high tilt angles

Technical specifications:

• Range of movement: +/- 5 degrees
• Radius of curvature: 65 mm
• Additional rear focus required: 15 mm
• Recommended distance to focal plane 55 mm from the male T-flange
• Thread: Male/Female T-Thread, M42x0.75
• Material: CNC machined aluminum
• Maximum camera weight: 3.5 kg (7.7 lb)
• Dimensions: 60x83 mm ellipse, 22 mm thick
• Weight: 0.1 kg (0.2 lb)

Daystar T-Mount Interference Corrector