Staring @ the Sun, 66a

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8/14/2014. Here are details of the Tilt-adapter mod. The page which links here has examples and some measurements of a mod intended to help eliminate Newton's rings. The rings are an interference effect which occurs when some cameras are mounted behind extremely narrow bandwidth filters such as the ones used for solar photography. The rings originate when monochromatic light bounces within the cover glass or between the cover glass and the sensor face. Tilting the gap defeats the inerference pattern and eliminates the rings. Clear, eh? Sometimes only a few snaps will do. Here's a reminder of what we're trying to accomplish:


ZWO Optical ASI120MM mounted on
a modified Teleskop-Service Tilt-Adjuster with 1.25-inch snout.
Physical dimensions are approximately to scale,
the 5.7° tilt angle is not exaggerated.


zwo tilt 1

Modified Tilt Adapter viewed from camera side.
1. Original pull bolts (removed) go (went) here.
2. Original push bolts (retracted, not used, left in place so as not to lose them).
3. New pull bolts (10-24, two different lengths)
4. New push bolts (10-24 "grub" screws, two different lengths)


zwo tilt 2

Side view. Camera goes at top, snout below.
3. New pull bolt, one of the long ones.
4. New push bolt, a long one.


zwo tilt 3

The relatively enormous gap in the tilt adapter will let in a lot of light when used in the noon-day Sun. I've rolled up a short bit of ProtoStar flocking material to use as a baffle. Black paper will do. Once adjusted to eliminate Newton's rings, I also wrap a few turns of black 'electrical' tape around the outside of the gap.


zwo tilt 4

Ready to go (except for the black-tape shroud around the gap).
One pull and one push bolt are in sharp focus near center.

Thanks to user "gabrieli" on Stephen Ramsden's invaluable "Solar Chat" forum
for pioneering the use of the T-S tilt adjuster in its stock configuration
to clean up Newton's rings in a PGR camera.


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Except where noted, solar photos are made with a ZWO Optical ASI120MM camera (ca. June 2013) behind a Lunt Solar Systems 60mm THa with its objective replaced by an Orion 90mm F10 achromat. The telescope uses a B600 blocking filter and is mounted piggyback with an Astro-Tech 10-inch Ritchey-Chretien (carefully capped!) on an Astro-Physics Mach1GTO mount. A Dell Latitude notebook running FireCapture provides camera control and capture services via USB 2.0. Images typically begin as 400 - 1200 frame AVI's captured at about 27 fps. Clips are aligned and stacked using AVIStack 2.0. The resulting files are processed via wavelet functions in Registax and / or the FocusMagic 3.0.2 deconvolution plug-in in Photoshop CS4. Alternatively, PixInsight picks up the processing somewhere in the workflow after AVIStack processing. The imaging train usually includes an Orion "Shorty" 2x barlow screwed into the ASI120MM body. A RoboFocus motor with a timing belt looped around the stock (or, sometimes, a Feathertouch) focus knob enables remote operation.



                   © 2013, David Cortner