Is the Esprit 120 the Best 4" to 5" Telescope for AP ?

[Big Bang!]

2 hours ago, Midnight_lightning said:

When balancing it with the EFW anywhere other than vertically up of down (home position) I can only get balance on one side of the pier or the other. So balance it one side and I can let go in any position and it just stays. Move to the other side and its not balanced. Took me a while to work it out but its because the CoG isn't symmetrical without the EFW vertical - it only affects Dec balance.

That doesn't sound quite right to me.  The distance to the pivot point doesn't change and so surely the "moment" doesn't change?   

Gus

[gorann]

3 minutes ago, Big Bang! said:

That doesn't sound quite right to me.  The distance to the pivot point doesn't change and so surely the "moment" doesn't change?   

Gus

Yes, it does not make sense to me either - if the weight does not change (and turning the optical train will not change its weight) then balance could not change, it seems to defy physics.

[RayD]

This video I did shows what he is talking about.  Off centre equipment affects the balance point on a third axis.

[Skipper Billy]

8 minutes ago, RayD said:

Off centre equipment affects the balance point on a third axis.

I was told way back to balance in all 3 axis and whilst the weight of the filter wheel off to one side makes little difference on my current rig on a previous rig which was a very light newt with an EFW2 and a heavy camera balancing the third axis made an enormous difference.

[RayD]

1 minute ago, Skipper Billy said:

I was told way back to balance in all 3 axis and whilst the weight of the filter wheel off to one side makes little difference on my current rig on a previous rig which was a very light newt with an EFW2 and a heavy camera balancing the third axis made an enormous difference.

Yes indeed, David.  Like you, on my Mesu you wouldn't even be able to determine if there was a difference, but when I got the CEM120 it made it really easy to show the issue.

[Skipper Billy]

Great video - it really shows the importance in a nice simple way. Well done.

[ollypenrice]

48 minutes ago, Big Bang! said:

That doesn't sound quite right to me.  The distance to the pivot point doesn't change and so surely the "moment" doesn't change?   

Gus

 

43 minutes ago, gorann said:

Yes, it does not make sense to me either - if the weight does not change (and turning the optical train will not change its weight) then balance could not change, it seems to defy physics.

 

6 minutes ago, RayD said:

This video I did shows what he is talking about.  Off centre equipment affects the balance point on a third axis.

Heh heh, I'm not very good at this 3D thinking. Ray's video highlights an important issue very neatly but does it account for a mount pointing at the zenith being in balance with C/W east but not west? Let's say Ray's adjustable weight, CW west, needs to be screwed away from the mount. That's towards the observatory wall, if there is an observatory wall. Now flip it so it's CW east. The adjustable weight is still going to be adjusted towards the observatory wall, so it should still be right.

I think the problem is more likely to arise from an increase in cable drag on one side and/or an increase in the amount of cable lifted on one side over the other.

We often meet this 3rd axis balancing business when trying to use deliberate imbalance to reduce the effects of backlash. In RA it's easy: you balance the mount east-heavy so the mesh always settles against the drive. You can't just do the same for Dec by being, say, camera end heavy because at the zenith this imbalance reduces to zero when the heavy camera end of the the OTA is directly beneath the light end.

3 axis balancing is not difficult and is vital on dual rigs. As well as the easy adjustment of Dec balance (slide scope forwards-backwards in tube rings) and RA balance (slide CW up-down shaft) you have to set the CW bar horizontal and ensure that the Dec axis will sit still with scope horizontal, vertical or anywhere in between. With the scope(s) vertical this means moving them in horizontal axis.

Olly

 

 

 

 

 

 

 

 

 

 

 

 

[gorann]

But then, what happens to the weight balance after a meridean flip?

[andrew s]

1 minute ago, gorann said:

But then, what happens to the weight balance after a meridean flip?

It will still be in balance. 

Regards Andrew 

[gorann]

1 minute ago, andrew s said:

It will still be in balance. 

Regards Andrew 

But then the filter wheel be pointing up instead of down (or vice versa), if that is supposed to matter (maybe I have to see the video).

[RayD]

Yes I think this is really only beneficial, as counter intuitive as it sounds, if your mount is pretty good and has very low levels of backlash on the dec axis.  If you have to balance one side heavy to engage mesh then this is going to largely negate the need for it.  The CEM120 is particularly good in this regard and it makes quite a difference when done.

Edited May 4, 2020 by RayD

[Midnight_lightning]

10 minutes ago, gorann said:

But then, what happens to the weight balance after a meridean flip?

I balance first then add a small weight to the east (Large Bulldog clip on the CW shaft or scope - with a piece of lead fishing weight attached).

After a flip I go outside and move the bulldog clip back to the east.

[andrew s]

10 minutes ago, gorann said:

But then the filter wheel be pointing up instead of down (or vice versa), if that is supposed to matter (maybe I have to see the video).

Basically,  you need to balance about  3 perpendicular axes.  Once it is balanced in 3 d it will stay balanced in any orientation ( assuming no cable drag).

With the dec axis horizontal you need to balance 1) about the ra axis 2) balance about the dec axis with the scope horizontal and 3) balance about the dec axis with the scope vertical.

 Regards Andrew 

Edited May 4, 2020 by andrew s

[gorann]

11 minutes ago, RayD said:

Yes I think this is really only beneficial, as counter intuitive as it sounds, if your mount is pretty good and has very low levels of backlash on the dec axis.  If you have to balance one side heavy to engage mesh then this is going to largely negate the need for this.  The CEM120 is particularly good in this regard and it makes quite a difference when done.

Well, I now saw the video. I never realized that this was so filddly - I may be saved by having a Mesu on one pier and an EQ8 on the other - I doubt they would bother about filter wheels sticking up or down. Hopefully, for Midnight Lightning this will not matter when he upgrades to a bigger mount.

Edited May 4, 2020 by gorann

[gorann]

Or if worrying about a filter wheel - why not just put a counter balance on it? A bit of fishing weights on the thin side.

[RayD]

1 minute ago, gorann said:

Well, I now saw the video. I never realized that this was so filddly - I may be saved by having an Mesu on one pier and an EQ8 on the other - I doubt they would bother about filter wheels sticking up or down. Hopefully, for Midnight Lightning this will not matter when he upgrades to a bigger mount.

Yes I have a Mesu too, Gorann, and it isn't really possible to get it this fine on the Mesu and certainly not a critical thing.  The CEM120 is very smooth as you will have seen, and it makes quite a bit of difference.

I think if someone is struggling with guiding at the zenith it is always worth checking, on a non friction drive mount.

[gorann]

1 minute ago, RayD said:

Yes I have a Mesu too, Gorann, and it isn't really possible to get it this fine on the Mesu and certainly not a critical thing.  The CEM120 is very smooth as you will have seen, and it makes quite a bit of difference.

I think if someone is struggling with guiding at the zenith it is always worth checking, on a non friction drive mount.

Yes, on our original Mesus that kind of balancing is not possible (no clutches), but a CEM120 is supposed to be able to carry 50 kg (I thought), so it should not matter much there either.

[RayD]

Just now, gorann said:

Yes, on our original Mesus that kind of balancing is not possible (no clutches), but a CEM120 is supposed to be able to carry 50 kg (I thought), so it should not matter much there either.

The CEM120 can definitely take that weight, but I think it's more about the guiding having to do less work than the weight.

I only linked the video to show what @Midnight_lightning was talking about as it can be a little hard to get your head around, so thought it would help.

[gorann]

19 minutes ago, RayD said:

The CEM120 can definitely take that weight, but I think it's more about the guiding having to do less work than the weight.

I only linked the video to show what @Midnight_lightning was talking about as it can be a little hard to get your head around, so thought it would help.

Yes Ray, I found it interesting, so thanks for the enlightenment! I do have a Star Adventurer too for travel and there it may of course make a difference. But his use of the little counter balance in the video tells me that you could easily make your filter wheel balanced with a bit of weight attached to the light side.

Edited May 4, 2020 by gorann

[Big Bang!]

Having seen the video I now understand.  Thank you.

Gus