I did a short experiment last night with barlows and focussing distances.<\/p>\n
The results baffle me so I am going to have to try it again.<\/p>\n
As a general rule of thumb, I had believed that using a focal reducer
\nwould bring the focus point in closer to the telescope and that a
\nbarlow would move the focus point further out from the telescope.<\/p>\n
In addition, I believed that the more powerful the barlow, the further
\nout the focus would be.<\/p>\n
So. I have a motorised focuser with a numerical counter. I moved the
\nfocuser all the way in, had a 90 deg diagonal and the zwo asi290mc
\ncamera installed, the following are the results<\/p>\n
focuser all the way in to start, position 0
\nno barlow -23000 to focus – quite a ways out
\nx1.5 antares barlow +3000 almost all in
\nx2 antares barlow -15000 maybe 1\/3 out
\nx2.5 televue barlow -4000 maybe 1\/4 out
\nx3 televue barlow +1000 maybe 1\/4 out<\/p>\n
Note that we started at zero and went negative the further out (that is
\njust the way the numbers went). So we should not have had any positive
\nnumbers at all.. and yet we did.<\/p>\n
How to account for that? slippage in the focuser motor, connection,
\netc? It was pretty cold (-4C) and it was moving pretty slow at times.<\/p>\n
In addition, the belief that the focuser would move further out with the
\npower of the barlow turned out to be not so.<\/p>\n
I think I will repeat this again. Then also repeat it with the starting
\npoint of the focuser all the way *out*.<\/p>\n
In any event, the whole purpose of this was to help with the catch22 of
\nimaging.. trying to find your out of focus target. you need focus to
\nsee the target but you need the target in order to focus. So I was
\ngoing to write these numbers down on the wall and use them to achieve
\n“close enough” focus in the first step, in aid of finding the target,
\nthen do a fine focus afterward.<\/p>\n","protected":false},"excerpt":{"rendered":"
I did a short experiment last night with barlows and focussing distances. The results baffle me so I am going to have to try it again. As a general rule of thumb, I had believed that using a focal reducer would bring the focus point in closer to the telescope and that a barlow would […]<\/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-9678","post","type-post","status-publish","format-standard","hentry","category-astronomy"],"_links":{"self":[{"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts\/9678","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=9678"}],"version-history":[{"count":1,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts\/9678\/revisions"}],"predecessor-version":[{"id":9679,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/posts\/9678\/revisions\/9679"}],"wp:attachment":[{"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/media?parent=9678"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/categories?post=9678"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starlightcascade.ca\/blog\/wp-json\/wp\/v2\/tags?post=9678"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}