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Date: 27 Jul 2007 07:59:22
From: brucegooglegroups
Subject: u tube videos; collimating secondary without peephole cap
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I have been frustrated with my poor views of Jupiter- even with
planetary filters- so I took a look at some of videos of amateur
astronomers view of Jupiter and Saturn, and the Moon on UTube.
Surprisingly- my view with a 4.5 Skyquest Dob is as good as most of
the telescopes used in the videos including the some of the larger
aperture scopes.
So I am beginning to see that the sky conditions are probably the
single most important factor in viewing. I am new to backyard
astronomy-over a year. I live in a semi rural area- which is vastly
better than the average viewer's viewing conditions. So aperture isn't
the final answer it seems, but it certainly enhances the view.
I have posted to this group about an issue with collimation. As I
suspected, my secondary is off. I am reading Robin Scagell's
Stargazing Through a Telescope which is very helpful. I realized that
by looking through the eyepiece holder without the eyepiece inserted
and looking at the image of my eye, I can see if the secondary is
aligned to primary. It is slightly off. It is slightly off center
towards the right- the same position as the black hole in the Donut
for a star test.
I have tried to align the secondary before without 100% success.
However, what about trying to align it without the peephole cap and
looking through the eyepiece area?
Bruce
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Date: 06 Aug 2007 14:49:15
From: brucegooglegroups
Subject: Re: u tube videos; collimating secondary without peephole cap
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On Jul 27, 1:48 pm, "Dennis Woos" <dpw...@gmavt.net > wrote:
> > I have tried to align the secondary before without 100% success.
> > However, what about trying to align it without the peephole cap and
> > looking through the eyepiece area?
>
> > Bruce
>
> The problem with not using a peephole is getting/keeping your eye properly
> aligned in the 1.25" drawtube.
>
> Get the physical positioning of the secondary as close as you can - centered
> in the tube (measure) and centered in the drawtube (peephole/eyeball) - but
> don't obsess over this as it is not nearly as important as the optical
> alignment. If you plan on sticking with observing then buy a laser
> collimator fromwww.collimator.com, which will help you to optically align
> the secondary and primary. Make sure that your primary is center-spotted
> accurately (measure), as this is the target for the laser. Finally, when you
> high-power star test only adjust the primary, never the secondary. If you
> have used the laser correctly then the star test should indicate that the
> collimation is right on or very close, requiring at most a small adjustment
> of the primary.
>
> Dennis
hi Dennis,
If the black hole in the donut in the star test is a true circle but
off slightly to the right, does this indicate that the primary is a
little off?
Thanks.
Bruce
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Date: 06 Aug 2007 19:07:14
From: Dennis Woos
Subject: Re: u tube videos; collimating secondary without peephole cap
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"brucegooglegroups" <brucegooglegroups@hotmail.com > wrote in message
news:1186436955.648588.200830@r34g2000hsd.googlegroups.com...
> On Jul 27, 1:48 pm, "Dennis Woos" <dpw...@gmavt.net> wrote:
>> > I have tried to align the secondary before without 100% success.
>> > However, what about trying to align it without the peephole cap and
>> > looking through the eyepiece area?
>>
>> > Bruce
>>
>> The problem with not using a peephole is getting/keeping your eye
>> properly
>> aligned in the 1.25" drawtube.
>>
>> Get the physical positioning of the secondary as close as you can -
>> centered
>> in the tube (measure) and centered in the drawtube (peephole/eyeball) -
>> but
>> don't obsess over this as it is not nearly as important as the optical
>> alignment. If you plan on sticking with observing then buy a laser
>> collimator fromwww.collimator.com, which will help you to optically align
>> the secondary and primary. Make sure that your primary is center-spotted
>> accurately (measure), as this is the target for the laser. Finally, when
>> you
>> high-power star test only adjust the primary, never the secondary. If you
>> have used the laser correctly then the star test should indicate that the
>> collimation is right on or very close, requiring at most a small
>> adjustment
>> of the primary.
>>
>> Dennis
>
> hi Dennis,
> If the black hole in the donut in the star test is a true circle but
> off slightly to the right, does this indicate that the primary is a
> little off?
> Thanks.
> Bruce
>
It does - so adjust one of the screws controlling the tilt of the primary a
very little bit and check again. It helps to have a helper, but is not
required.
Dennis
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Date: 04 Aug 2007 07:17:31
From:
Subject: Re: u tube videos; collimating secondary without peephole cap
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On Jul 27, 12:01 pm, Margo Schulter <mschul...@web1.calweb.com > wrote:
> brucegooglegroups <brucegooglegro...@hotmail.com> wrote:
>
> > I have tried toalignthe secondary before without 100% success.
> > However, what about trying toalignit without the peephole cap and
> > looking through the eyepiece area?
>
> > Bruce
>
> Hello, there, Bruce.
>
> As someone new at this, I understand that two possibilities would be
> either to try laser collimation as Dennis has suggested, or to try a
> dedicated collimation eyepiece of the Cheshire variety such as are
> made available by Orion and Celestron. Some people use both methods,
> and each may have its advantages.
>
Hi
Why not make a simple peep hole. I have one I made from a 35mm
film can ( plastic ). I just drilled a small hole in it and cut the
lip end
off.
Another was is just a simple cardboard peep hole. Take a cereal
box and cut a couple of 1/4 strips. Roll these so that they form rings
in your focuser. Take another piece of cardboard and make a disk
that fits into the focuser smuggly. Put a hole in the middle of it
as the peep hole. Use the cardboard rings you made to keep it
straight in the focuser tube.
I thought I'd mention here that the secondary alignment can be so far
off that you can't see anything, most minor missalignment will only
cause slight vinetting at the edges of the lower power eyepieces.
Alignement of the primary is much more important for sharpest
image.
Before starting optical secondary alignment through the peep hole,
first
check that it is centered right and left in the tube. If you have a
faster
telescope ( below f5 ), also include the offset wasy from the focuser.
There are several web pages that describe this caclulation. Slower
telescopes, it is usually so small as to not have much effect.
It should be noted here that if the offset is not correct, when done
with the opical alignment, the center of the optical path will not
be aligned with the physical tube. If the secondary is placed without
proper offset, the optical axis will be tilted slightly towards the
focuser
and could cause slight vinetting, caused by the front opening of the
telescope tube( not as big a deal as many seem to think it is and for
poorer mirror, might even inprove image quality ).
Once you are happy with the mechanical placement of the secondary,
work on the optical. Keep in mind that many of the adjustments
needed in the optical alignment of the secondary my interact with
the mecahnical centering. Consider that this optical is only tilting
of the secondary unless the focuser tube is poorly aligned.
The focuser can often be aligned by shimming it at the mount points.
The right left is usually most important while the up/down only
effect the position of the secondary along the primary axis.
( I'm assuming that the primary tube is pointing straight up ).
Focuser alignement can be checked by looking along the edges
of the focuser tube. You shold see the same amount of secondary
edge from all edges of the focuser.
Dwight
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Date: 27 Jul 2007 19:01:34
From: Margo Schulter
Subject: Re: u tube videos; collimating secondary without peephole cap
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brucegooglegroups <brucegooglegroups@hotmail.com > wrote:
>
> I have tried to align the secondary before without 100% success.
> However, what about trying to align it without the peephole cap and
> looking through the eyepiece area?
>
> Bruce
>
Hello, there, Bruce.
As someone new at this, I understand that two possibilities would be
either to try laser collimation as Dennis has suggested, or to try a
dedicated collimation eyepiece of the Cheshire variety such as are
made available by Orion and Celestron. Some people use both methods,
and each may have its advantages.
The secondary mirror adjustment that I understand is adjusting some
screws or bolts, as explained in a telescope's instruction manual,
to that all the primary mirror clips (three for my 20cm Dob, and also
three in the more general illustration in the instruction sheet for
my Orion collimation eyepiece) are visible in the collimation cap
or eyepiece.
However, I know that there can be other positioning issues with the
secondary mirror, also, which aren't mentioned in the manual for my
scope but are discussed as a preliminary step in the short Orion
manual I've mentioned before adjusting the secondary mirror to get
all the primary mirror clips visible, and then adjusting the
primary mirror so that secondary mirror reflection is centered.
Again, I'd emphasize that while at least the last two familiar
steps are common to Newtonian reflectors, as far as I understand
it, the specific mechanics can vary from scope to scope, so the
manual can be helpful. Also, I much like some earlier advice in
what looked like a thread related to your earlier posting: if you
have means of transportation and can get your scope to a star party
or the like, this could be a fine opportunity both to check out
the performance of your scope against others under the same
atmospheric seeing or turbulence, etc.; and to get a bit of help
with collimation if it's needed.
Most appreciatively,
Margo Schulter
mschulter@calweb.com
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Date: 27 Jul 2007 13:48:48
From: Dennis Woos
Subject: Re: u tube videos; collimating secondary without peephole cap
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> I have tried to align the secondary before without 100% success.
> However, what about trying to align it without the peephole cap and
> looking through the eyepiece area?
>
> Bruce
The problem with not using a peephole is getting/keeping your eye properly
aligned in the 1.25" drawtube.
Get the physical positioning of the secondary as close as you can - centered
in the tube (measure) and centered in the drawtube (peephole/eyeball) - but
don't obsess over this as it is not nearly as important as the optical
alignment. If you plan on sticking with observing then buy a laser
collimator from www.collimator.com, which will help you to optically align
the secondary and primary. Make sure that your primary is center-spotted
accurately (measure), as this is the target for the laser. Finally, when you
high-power star test only adjust the primary, never the secondary. If you
have used the laser correctly then the star test should indicate that the
collimation is right on or very close, requiring at most a small adjustment
of the primary.
Dennis
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