Hi
This is an interesting idea but I would think there would be an issue.
The artificial star must be high enough that the scope is in an
"observing" attitude and far enough away to get the focuser in the proper
area also.
This is a problem with "daylight" collimation techniques for SCTs. The
artificial star ends up mounted where you can reach it and also it has to
be far enough away so that the focuser is in its "normal" position.
The "artificial star" I use is a red laser pointer aimed at a ball with an
external reflective coating (i.e. a Christmas ornament). The reflection
is sharp enough at a reasonable distance that collimation is possible at
insane magnifications. (good collimation can only be done at very high
mags - for an SCT this is above 40x per inch and 50x per inch (of
aperture). It has to be high enough so you can see "in focus"
diffraction rings.
The issues on an SCT is that the primary doesnt sit the same way with the
scope horizontal as it does with the scope vertical. A second one is
where the primary is for the collimation test. This is a focus issue.
The focus adjustment can change the optical center of the ep if everything
is not exactly square. These issues have counterparts in Newts as you all
were discussing.
---------
Phil Chambers [ptchamb-at-svpal.org] (S.F. Bay Area - Calif. USA)
On Fri, 14 Mar 2008, Matthew Marcus wrote:
> It sounds as if what's needed is a collimation shoot-out, in which a scope is
> intentionally
> de-collimated, then somebody collimates it, tests it, and then the cycle is
> reapeated with
> another collimation challenger. Now, one problem with this idea is that
> nights with seeing good
> enough to allow subtle differences to show are pretty rare in our area.
> Enter the artificial star.
> What I propose is that an artificial star be set up at one end of a long site
> and one or more
> scopes at the other. For an objective read on the quality, it might be
> worthwhile to image using one
> of those quick planetary cams. The test should probably occur at night to
> avoid 'seeing' due to
> hot air coming off the ground between scope and artificial star. That would
> also reduce any background
> light in the images, making quantitative analysis simpler. Yes, this is a
> big effort, but it might
> be worthwhile to do it once and get the data.
>
> Of course, I speak as someone who does not own a Dob.
> mam
>
> Michelle Stone wrote:
>> Albert and I have discussed this collimation issue several times. I
>> know that I commit heresy every time the subject comes up. Once you
>> get a good scope with good optics aligned correctly, some error in
>> collimation is perfectly acceptable and can not be seen at the
>> eyepiece. There are many other factors in the complete telescope that
>> affect the image beyond collimation.
>>
>> I have observed with Dan Grey many times and used his scope. It is a
>> wondrous creation. Looking up into the eyepiece is a bit difficult
>> for me on this scope due to a neck injury that I've had for many
>> years. But it is well worth looking! Dan is always so willing to
>> share views. If you run into him at a star party, you must avail
>> yourself to his hospitality.
>>
>> As far as laser collimators go, I really like Howie Glatter's
>> products. They have some nice options and offer a barllowed feature
>> that helps take care of additional alignment concerns. My personal
>> laser is an old Astrosystems single point unit that has served me well
>> for many years.
>>
>> You know, I'm thrilled that we are having this conversation. It is
>> very worthwhile and fun!
>>
>> Michelle
>>
>> On Fri, Mar 14, 2008 at 12:59 PM, Mark Wagner
>> <mark.wagner@No-Spam> wrote:
>>
>>> Albert wrote:
>>>
>>> > This armchair speculation is interesting. I suggest we arm ourselves
>>> with collimators, introduce
>>> > known deviations into our scopes, and check visually what important.
>>> Anyone up for some
>>> > experimentation?
>>>
>>> I was going to suggest a collimation "experimentation seminar" at GSSP. I
>>> think there would be
>>> lots of interested people there...
>>>
>>> Also, Albert, I agree that it can become kind of an absurd pursuit,
>>> getting "prefect" collimation.
>>> There is a point of greatly diminishing return, for visual applications.
>>> And, as said before, the
>>> slower the scope, the more tolerant it becomes.
>>> --
>>> GSSP Attendees Page updated 3/14/08: http://www.goldenstatestarparty.org
>>>
>>>
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>>>
>
> --
> GSSP Attendees Page updated 3/14/08: http://www.goldenstatestarparty.org
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>
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Received on Fri Mar 14 15:10:17 2008