Re: [OT] Telescope
- From: "Yowie" <yowie9644.DIESPAMDIE@xxxxxxxxxxxx>
- Date: Mon, 5 Jan 2009 20:41:00 +1100
"Tom McDonald" <tmcdonald2672@xxxxxxxxxxx> wrote in message
news:uq38l.53370$lX6.32304@xxxxxxxxxxxx
Yowie wrote:
I mentioned that I was looking at getting a telescope here recently.
Problem solved: my husband got me one for Christmas - a Celestron
AZ76 (Newtonian). It prestty much bottome of the range but it does
the job and does it much better than my old Tesco one.
One problem I have with it is the tripod being unstable, such that
the tripod often moves rather than the scope itself, but my biggest
problem by far with viewing the night sky has nothing to do with the
scope but my seeming irresistability to all forms of biting insect.
I can only stand to be out on a summer night for about 15 minutes
before the itching becomes intolerable and I have to retreat inside.
There are other niggles, but its still a cool 'scope and the moon
looks wonderful through it.
Great news! Now a couple of questions:
Is this the scope you got:
PowerSeeker 76mm x 700mm alt-azimuth reflector
* Alt-azimuth mount with adjustable height aluminium tripod
and accessory tray
* 5 x 24 finderscope
* 3x Barlow lens
* 4mm + 20mm 1.25" eyepieces
* "The Sky - Level 1" CD-ROM included
Thats the one!
If so, then you might try using the scope with the legs not fully
extended, and observing while sitting. This could help steady the
mount.
Did that - helps enormously with my back, didn't helP so much moving the
scope around. The other niggle is that the finderscope doesn't directly line
up scope proper such that I have to look at anything, I first haveto place
it
int he finderscope at about the 2pm position, 2/3 of the radius away from
the intersection of the cross hairs. OK for the moon, exceptionally annoying
for points like stars. I don't know whether I've mounted it wrong or whether
its adjustable.
What kind of eyepieces do you have? Are they Huygens, or Kellner,
or Plossel? (They may be marked with the name next to the size in
mm; or they may have an initial next to the size in mm.)
If they are Huygens, unless you have very good eyesight, you will
probably find it easier to get higher power using the 20mm
eyepiece with the Barlow lens than with the 4mm eyepiece.
I have no idea, they're whatever came with the scope and are simply marked
'20mm' and '4mm'. I had no problem viewing the moon with the 4mm one, but
found that it moved through the field of vision annoyingly quickly and went
back to just using the 20mm one - with which the whole of the moon is
visible in the field of view. Looks magnificent too - any idea how to get a
decent photo of the image using a relatively cheap point-and-shoot digital
camera?
The problem here is eye relief -- the distance between the
top-most bit of glass in the eyepiece and your eye. Huygens
eyepieces have pretty short eye relief, and the 4mm eyepiece will
probably have your eyelashes brushing the eyepiece. Using the
Barlow with the 20mm eyepiece, the eye relief is the same as
using the 20mm by itself.
OTOH, if you do have Huygens eyepieces, they are probably not
cemented in place. This will make them useful for projecting
images of the sun at magnification on white card stock. Using
more complex, cemented lenses for this purpose is not a good
idea, as the heat from the sun through the scope can melt the
cement. Not a good thing.
I don't have any solar filters and probably won't do any solar astronomy -
far too dangerous for my 4yo boy to even *think* about observing the sun. If
he develops an interest in astronomy (which I hope he does) then when he has
some sense in his head we might, but not until then (and if he does become
interested, then we'll probably get a better scope with an equitorial mount.
The rule of thumb for determining a scope's maximum useful
magnification, under perfect seeing conditions, is about 50X per
inch of scope aperture. With a 76mm (call it 3 inch) aperture,
the best you are likely to get is about 150X. The 4mm eyepiece at
700mm focal length will give you 175X. (With the Barlow, the 4mm
will give you ~540X! Expect pretty colors, but not a clear view
of anything.)
If you can see anything clearly at 175X, you should consider
yourself very lucky. :-) (But most astronomers get lucky now and
again, so cherish the event when it happens to you!)
Got lucky with the moon :-)
Managed to line up Venus with the 20mm, and not surprisingly it looked like
a blob of bright light. By that time my patience with The Itch had pretty
much run out and I knocked the cope putting the 4mm in. And at that point
gave, went inside and doused myself with roll-on deodarant (stops mozzie
itches very well - its the same stuff as Stingose)
The AZ mount will probably be just fine for terrestrial viewing.
I think the scope comes with a correcting lens, so that what you
see is right-side-up and correct left-to-right.
It says it does, and it seems to intuitively work like that - if the Moon is
'moving' out of the field of vision to the left, moving the 'scope to the
left brings it back. I am very grateful for this feature, I am not
particular strong in my spatial awareness (every accident/bingle bar one has
been whilst parking) and having things backwards would infuriate me.
The AZ mount is, as you know, harder to use for astronomy. It
almost certainly does not move as smoothly as you need it to to
keep things in view, especially when using higher magnification.
You may find that it gets better as you use it more; both because
that may work out some of the stiffness in the mechanism, and
because you will get better at using it with practice.
It does have a 'fine' adjuster for altitude, which is useful, its the lack
of smoothness in the movement that is annoying. At the moment, the vertical
has a small amount of slack in it, and the horizontal has a bit of bounce so
I have to slighly overcorrect and let it bounce back. Again, these are
*niggles* and may or may not sort themselves as I use it and get used to it.
And I'll get some 'aeroguard' for the mozzies :-)
Yowie
My, how I do go on! Perhaps it is because I'm jealous. I had to
sell my scopes, so now I astronomize vicariously through the
experiences of others.
BTW, if you can get some bug spray with DEET, and can tolerate
the DEET, use it. Just be very careful not to get it on any of
the glass. It is probably best to avoid, for instance, citronella
torches or candles, as the smoke may get onto the glass.
--
If you're paddling upstream in a canoe and a wheel falls off, how many
pancakes can you fit in a doghouse? None, icecream doesn't have bones.
.
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