{"id":9687,"date":"2021-12-07T10:16:28","date_gmt":"2021-12-07T14:16:28","guid":{"rendered":"https:\/\/starlightcascade.ca\/blog\/?p=9687"},"modified":"2021-12-11T14:00:48","modified_gmt":"2021-12-11T18:00:48","slug":"collimate-collimate-collimate","status":"publish","type":"post","link":"https:\/\/starlightcascade.ca\/blog\/2021\/12\/collimate-collimate-collimate\/","title":{"rendered":"collimate! collimate! collimate!"},"content":{"rendered":"

\"\"<\/a><\/p>\n

Telescope optics tend to be a finicky and complex issue at times. Mirrors tend to be finished down to fractions of a wavelength of light across the mirror surface to its designed curve.<\/p>\n

The vixen VC200L is a 200mm diameter mirror with a focal ratio of 9 meaning it has a focal length of 200*9=1800mm.<\/p>\n

Now imagine the sensitivity of a mirror out to a point 1.8m away. The slightest movement of the mirror throws the focus point off by a lot.
\nAlso consider camera pixels, which are on the order of 5 micrometers..
\nSo.. We had a problem. Our imaging of Jupiter was not coming into focus.<\/p>\n

\"\"
35mm film canister<\/a><\/figcaption><\/figure>Normally the first thing you think of is the collimation. So we used a 35mm film canister with a whole in the centre to do a rough test. It did not look too bad.<\/p>\n

\"\"Cheshire collimator<\/a>
\nThen we used a cheshire collimator.
\nIt too looked ok but the cheshire was not fixed symmetrically in the focuser when you rotated it 360 degrees around. As a result the optics looked really bad.. but you did not know that for a fact..<\/p>\n

Lastly the star test.
\nWe used only the 90deg adapter, no barlow, and the zwo asi224mc and zwo asi290mc cameras.
\nWow! The asymmetry jumps out at you:<\/p>\n

\"\"2021nov27-badcollimation<\/a><\/p>\n

This is the bright star Vega, inside the focus point. Running it through the focus point and outside the focus point also shows bad collimation.<\/p>\n

So we waited until the skies cleared again, determined that the vixen collimation screws\/allen screws, used a 2.5mm allen key. We identified the push screws by loosening one and seeing that it was indeed loose. All three push screws were loosened. The camera was fired up and the out of focus start was displayed.
\nStarting at a standard fixed point, we adjusted the pull screw and the image went out of the field of view. So it was a turn the screw and use the telescope handcontroller to move the scope and keep the image on display. After a few 1\/6 turns, we moved to another screw and repeated. It still seemed out a bit so we went to the 3rd push screw and pushed it in a bit.
\nThe star test image looked *much* better:<\/p>\n

\"\"2021dec03-after collimation<\/a><\/p>\n

This is Vega inside of focus.
\nCloser inspection shows the collimation can still be improved just a little bit more… next clear night!<\/p>\n

The Jupiter images have not yet been processed but they do look better!<\/p>\n","protected":false},"excerpt":{"rendered":"

Telescope optics tend to be a finicky and complex issue at times. Mirrors tend to be finished down to fractions of a wavelength of light across the mirror surface to its designed curve. The vixen VC200L is a 200mm diameter mirror with a focal ratio of 9 meaning it has a focal length of 200*9=1800mm. […]<\/p>\n","protected":false},"author":494,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[],"class_list":["post-9687","post","type-post","status-publish","format-standard","hentry","category-astronomy"],"_links":{"self":[{"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts\/9687","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/users\/494"}],"replies":[{"embeddable":true,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/comments?post=9687"}],"version-history":[{"count":16,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts\/9687\/revisions"}],"predecessor-version":[{"id":9713,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts\/9687\/revisions\/9713"}],"wp:attachment":[{"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/media?parent=9687"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/categories?post=9687"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/tags?post=9687"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}