DIY artificial star for SCT collimation

Using a Schmidt-Cassegrain telescope (SCT) like my Celestron NexStar 6SE requires the secondary mirror to be collimated properly to get a crisp image. I've done the collimation after fixing the screws, but I wanted to fine-tune further. The adjustment I will be making won't be the definitive for all the cases because the gravity affects the secondary mirror subtly with differing angles. But because the diameter (and consequently, weight) of the mirror is relatively small the deviation after the fine adjustment was hoped to be small.

Ready to modify the LED flashlight

Unfortunately, the real stars often look too shaky, so I decided to try the artificial star method for this tuning instead. An artificial star is basically a bright light source coming from a tiny hole. For the light source, I do indeed have one - an LED flashlight that I bought many years ago. It's actually an external battery for charging phones with a bright LED as a bonus feature, but it's so old that the charging port is a Korean 24-pin standard that was popular about a decade prior. Now it was time for this little gadget to be useful again.

Punching a hole with a pin

I initially tried it out as is, but the LED part was too big. It was time for a little modification. After trying out different materials, I found that a sheet of back cover for making presentation handouts was effective at blocking light, yet did not require complicated tools to work with. A pair of scissors let me cut one up to make a cover over the flashlight. Next, I punched a tiny hole where the LED was supposed to be at.

One simple DIY artificial star ready for use

Finally, the edges were glued together. With this simple paper cover on, the light would now only be able to shine through the hole. It was just what I wanted, and I set it up at one end of the living room.

Collimating the telescope with the artificial star and a camera

The telescope was then placed at the other end of the room, about 6m(20ft) away from the light. To aid in the adjustments, I put my Sony A5000 on the telescope instead of an eyepiece. The camera was linked to my iPhone 6S Plus to be controlled remotely.

Observing the collimation ring on the remote camera control app

I considered this to be quite helpful because I could evaluate the out-of-focus ring of the artificial star away from the telescope, mitigating a possible source of distortion. Also, it allowed me to use the screen magnification feature of the iPhone to see the ring's distortion more clearly than the camera's own live view screen.

All in all, the simple DIY artificial star, along with a camera and a smartphone let me do a stable fine collimation of my telescope in the comfort of my home. When the sky clears up, I'll check to see how well this helped.

Trackbacks

Trackback specific URI for this entry

This link is not meant to be clicked. It contains the trackback URI for this entry. You can use this URI to send ping- & trackbacks from your own blog to this entry. To copy the link, right click and select "Copy Shortcut" in Internet Explorer or "Copy Link Location" in Mozilla.

No Trackbacks

Comments

Display comments as Linear | Threaded

No comments

Add Comment

E-Mail addresses will not be displayed and will only be used for E-Mail notifications.

To prevent automated Bots from commentspamming, please enter the string you see in the image below in the appropriate input box. Your comment will only be submitted if the strings match. Please ensure that your browser supports and accepts cookies, or your comment cannot be verified correctly.
CAPTCHA

Enclosing asterisks marks text as bold (*word*), underscore are made via _word_.
Standard emoticons like :-) and ;-) are converted to images.

Copyright (C) 1996-2024 Woo-Duk Chung (Wesley Woo-Duk Hwang-Chung). All rights reserved.