Counterweight (ETX-90PE with Canon EOS300D)

I've just bought a T-Mount and adapter ring for my Meade ETX-90PE, to
attach my Canon EOS300D. Overall, the weight of the camera and
mountings is about 0.85kg.

Given that the camera extends quite a way off the back of the
telescope, I'm going to need something more than the 0.85kg weight on
the other end. There's a couple of screw holes underneath where I can
attach a counterbalance - obviously it'll have to have an extension
rod on it. The question is this: Will I need to add more than the
0.85kg in weight on the counterbalance, due to the fact that the
camera extends out so far behind (it's about 5-6 inches)?

The screw mounting is attached to the plastic part of the body and
adding this much weight would worry me. I guess I could always find
some way of getting some weight and using a rubber strap on the end of
the scope to add some extra mass.

On or about 2007-03-07,
Rexx Magnus illuminated us with:
I've just bought a T-Mount and adapter ring for my Meade ETX-90PE, to
attach my Canon EOS300D. Overall, the weight of the camera and
mountings is about 0.85kg.

I've been considering doing this very thing with my ETX-105 and 350D.

Given that the camera extends quite a way off the back of the
telescope, I'm going to need something more than the 0.85kg weight on
the other end. There's a couple of screw holes underneath where I can
attach a counterbalance - obviously it'll have to have an extension
rod on it. The question is this: Will I need to add more than the
0.85kg in weight on the counterbalance, due to the fact that the
camera extends out so far behind (it's about 5-6 inches)?

That surely depends on how long the extension rod is. You can try to
calculate what you need using fairly simple sums (Mass x distance from
pivot needs to match) and then refine it from experience. However, I'd
be careful about overloading the bearings on the telescope and more
likely overloading the drive.

The screw mounting is attached to the plastic part of the body and
adding this much weight would worry me. I guess I could always find
some way of getting some weight and using a rubber strap on the end of
the scope to add some extra mass.

I'm guessing from your description that you're attaching the camera to
the rear connector, and you've flipped the mirror out of the way. Is
it not possible to attach it to the top connector, so that the camera
CofG is nearer the telescope pivot?

--
Mark
Real email address | Why is lemon juice made with artificial flavor, while
is mark at | dishwashing liquid is made with real lemons?
ayliffe dot org |

On Wed, 07 Mar 2007 13:41:33 GMT, Mark Ayliffe wrote:

On or about 2007-03-07,
Rexx Magnus illuminated us with:

The screw mounting is attached to the plastic part of the body
and adding this much weight would worry me. I guess I could
always find some way of getting some weight and using a rubber
strap on the end of the scope to add some extra mass.

I'm guessing from your description that you're attaching the
camera to the rear connector, and you've flipped the mirror out of
the way. Is it not possible to attach it to the top connector, so
that the camera CofG is nearer the telescope pivot?


It would be possible, with a 1.25" eyepiece adapter, but that idea
didn't seem as secure as using the end mounting. I stumbled across a
page where someone put weights on a dew shield and did it that way:

http://www.dirtyskies.com/index.php/...-mount-better-
moon/

Thinking about it a little more, I might be able to bodge up
something that works in a similar way by using a bar that bolts onto
the underside, with a supporting hoop to go over the end of the
tube. Weights could then be hung from the end of the bar, below the
objective lens, on a pivot.

--
http://www.rexx.co.uk
To email me, visit the site.

http://www.rexx.co.uk/runes/ - personal online rune readings

"Rexx Magnus" wrote in message
...

ETX105 - I used a length of screwed rod with a counterweight adjustable more
or less anywhere along the length. Found the correct position by slackening
off the elevation clamp. If you are using the telescope in polar mode, you
may need to rebalance (from memory). Seem to remember that initial setting
up was best done without camera etc. attached.
Make sure that your camera doesn't hit the ETX base during the alignment
procedure.

Good luck
--
M Stewart
Milton Keynes, UK



--
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On Thu, 08 Mar 2007 17:55:35 GMT, Malcolm Stewart wrote:

ETX105 - I used a length of screwed rod with a counterweight
adjustable more or less anywhere along the length. Found the
correct position by slackening off the elevation clamp. If you
are using the telescope in polar mode, you may need to rebalance
(from memory). Seem to remember that initial setting up was best
done without camera etc. attached. Make sure that your camera
doesn't hit the ETX base during the alignment procedure.

Good luck

Yeah, I tried polar mounting last night - and realized that the
camera would be inside the base, due to the home position being
vertical!

--
http://www.rexx.co.uk
To email me, visit the site.

http://www.rexx.co.uk/runes/ - personal online rune readings

On or about 2007-03-07,
Rexx Magnus illuminated us with:
On Wed, 07 Mar 2007 13:41:33 GMT, Mark Ayliffe wrote:

On or about 2007-03-07,
Rexx Magnus illuminated us with:

The screw mounting is attached to the plastic part of the body
and adding this much weight would worry me. I guess I could
always find some way of getting some weight and using a rubber
strap on the end of the scope to add some extra mass.

I'm guessing from your description that you're attaching the
camera to the rear connector, and you've flipped the mirror out of
the way. Is it not possible to attach it to the top connector, so
that the camera CofG is nearer the telescope pivot?


It would be possible, with a 1.25" eyepiece adapter, but that idea
didn't seem as secure as using the end mounting. I stumbled across a
page where someone put weights on a dew shield and did it that way:

http://www.dirtyskies.com/index.php/...-mount-better-
moon/

Thinking about it a little more, I might be able to bodge up
something that works in a similar way by using a bar that bolts onto
the underside, with a supporting hoop to go over the end of the
tube. Weights could then be hung from the end of the bar, below the
objective lens, on a pivot.

OK, I got mine set up and tried it last night. The 350D uses the
normal top connector on my ETX-105 and I found that a 1/2 kg
wrist/ankle exercise weight strapped around the objective end of the
tube counterbalances it nicely for most elevations. I get a
surprisingly large field of view, contra the Meade LPI which is only
tiny, I guess I'll be using the Barlow more.

Now all I need to do is work on focus and getting the exposure right
and I may even have some worthwhile pictures!

--
Mark
Real email address |
is mark at | Some people march to a different drummer and some people polka.
ayliffe dot org |