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  #41  
Old 23-09-2008, 03:33 PM
gary
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Hi Rob,

Thanks for the post.

Quote:
Originally Posted by CoombellKid View Post
Thanks for the tips, I went out and tried them late last night. Can I still
have Refraction On when I have Auto Adjust On?
Absolutely and we recommend this.

The following background may also be of interest.

What AUTO ADJUST ON does is looks at the angular distance between the
two stars (as a function of time to compensate for Earth rotation) and
looks at the angular distance the encoders *appeared* to move (based on
the initial 'hint' value you gave for the Alt encoder reference point).
If you had got the initial 'hint' value *exactly* correct, these two
angles would be exactly equal (when AUTO ADJUST is OFF, the WARP value
is in degrees and is in fact the difference in degrees between these two
angles). However, chances are you will not have got the initial hint
value exactly right. This is where AUTO ADJUST kicks in. It moves the
Alt encoder zero reference point so that the two angles are exactly the
same and therefore the WARP factor will be zero.

AUTO ADJUST ON can do a wonderful job in refining the ALT REF point.
However, it is also a case of "garbage in, garbage out". For example, if
the user mis-identifies one or both alignment stars, AUTO ADJUST will
"bend over backwards" to make the distance the encoders moved match the
distance between the two stars, even if this means moving the Alt Ref
point to an angle that is far away from the initial "hint" value.
Similarly if the wrong number of encoder steps are set or there is a
mechanical slippage in an encoder. AUTO ADJUST ON will try and do the
right thing and give you a WARP factor of zero, but it does not mean
your pointing will then be precise because it will have incorrectly
compensated in face of these more serious problems.

What we recommend for users to do is to initially test the system with
ALT REF = 90 degrees AUTO ADJUST OFF. In fact, when we designed the unit
we could have made the decision to have AUTO ADJUST ON at all times.
However, AUTO ADJUST can incorrectly compensate for a large class of
problems and thereby 'mask' the problem. For this reason, we make users
conscious of the FIX ALT REF step and allow them to switch AUTO ADJUST
OFF so they can help diagnose a problem for themselves.

As I recommended, never become too preoccupied with the initial manual
setting of the ALT REF point and you can put aside mechanical
aids such as spirit levels and set-squares. AUTO ADJUST ON is
your friend. However, if something seems amiss, the ability to
switch it OFF for a while can help you diagnose a problem.

Argo Navis allows you to see what value AUTO ADJUST ON moved
the Alt encoder reference point to. After you do the FIX ALT REF (with
AUTO ADJUST ON) and the two star alignment, place the unit in MODE
ENCODER. Push the scope back to the zenith stop position and read the
right hand (Alt encoder) value. It should be in the ball-park of 90
degrees. If it is more than a few degrees of either side of this, you
likely have a mechanical problem somewhere.

With regards refraction compensation, as you are aware, this becomes
important close to the horizon, a part of the sky most Dob owners tend
to shun. Refraction modeling uses your lat/long (that of your nearest major
town is fine) along with your time zone and local time. From the location
and timezone and local time, Argo Navis can then compute where the
local horizon is and then apply the necessary corrections. Currently at your
locale, your time zone setting will be +10:00 hours.

Quote:
Having Auto Adjust On, seemed to work ok. I tend to find the alignment
error happens when I do an Align Star in the west and then swing and look
at something in the east. But I also found if I did an Mode Align on the
object (with Auto Adjust On) seemed to fix it, is that how it should work?
I have a feeling this could some sort of mount error. I'll perform a TPAS
once I've become comfortable with what I'm doing.
In the face of mount fabrication errors (all mounts have them to some extent)
the pointing error residuals will be smallest in the neighborhood of the two
alignment stars. Therefore one strategy is to choose one of the two alignment
stars to be in the area of the sky in which you plan to initially observe. If you
then move to some new part of the sky and find that the error residuals have
increased, one can align on a new object in that area. You can align on
any type of object, including for the initial alignment objects, but stars and
plans are best since their astrometric co-ordinates don't suffer the same
uncertainties that extended objects, such as nebula and galaxies, do.

Argo Navis maintains a queue of alignment objects, and the default setting,
which we recommend, is two objects deep. For true multi-star alignment, this
is where TPAS comes into play.

Quote:
I think I logged 100+ objects last night through to 1:30am this morning. I
think that would have to be a record for me. It was fairly clear with
trans 7/10 but a touch windy. Which made setting the Mode Fix Alt Ref
a bit hard. Turning on Auto Adjust made that a lot easier.
Brilliant and great to hear that it was a new personal record observing run!

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Fax +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
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  #42  
Old 23-09-2008, 08:24 PM
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desler
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Happy Happy Happy!

Whilst I can't claim to be anything more than a novice. I can't believe how good this unit is. I've just finished a tour, to mag 10 of the LMC, which I cant even see naked eye, due to my light polluted back yard.

Whilst mag 8+ are little more than fuzzy blobs from downtown Werribee, I couldn't be happier.

I agree that the tweaking and playing around can be frustrating, but it's 9.21pm and I've seen more in the last hour, than I used to see in a months worth of star hopping.

Happy days..........

Darren
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  #43  
Old 24-09-2008, 10:32 AM
gary
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Quote:
Originally Posted by desler View Post
Whilst I can't claim to be anything more than a novice. I can't believe how good this unit is. I've just finished a tour, to mag 10 of the LMC, which I cant even see naked eye, due to my light polluted back yard.
Hi Darren,

Thanks for the post and fabulous to hear you are getting such productive use
from your Argo Navis.

Since most of us live in cities and large towns, your issues with light
pollution are unfortunately the norm rather than the exception. However,
it is amazing how many objects you can observe in less than optimal conditions
such as this, particularly when you know the object you are looking for
is in the eyepiece in the first place. Many a time I have been surprised to
observe objects under such conditions that I had initially suspected would
be impossible to see. The majority of users also have work and family
commitments, so more often than not, a few hours observing from their own
backyard is a luxury in itself, particularly since we live in a world where spare
time often comes at a premium.

Speaking of the LMC, you will be undoubtedly pleased to know that considerable
effort went into the compilation of the catalogs and that the LMC and SMC are
particularly well covered. Many thanks go to Andrew Murrell who acted as
a consultant during the compilation of objects within the Magellanic Clouds
and there is comparatively so little literature on objects within them that it
got down to Andrew getting out the 20" reflector and observing them with him.
One can spend weeks within the SMC alone!

Enjoy the journey!

Best regards

Gary
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  #44  
Old 24-09-2008, 11:40 AM
ausastronomer (John Bambury)
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Hi Rob,

I just wanted to add a few tips to Gary's very detailed comments based on my practical experience of having used several Argo Navis units on dobs ranging from 8" to 25" over the past 5 years or so.

On "any" hand made dob there will always be "mount fabrication errors". If you are a fine wood craftsmen these will be minimal and likely go undetected in normal use of Argo Navis, however in most cases they can lead to detectable pointing inaccuracies caused by the mount. On a couple of scopes I have seen they are significant. As Gary alluded to these will manifest as larger pointing errors when pointing to parts of the sky farthest away from your original alignment stars. This is where TPAS is your very very best friend. Whilst its use and implementaion may appear a little daunting at first it is very easy to use and truly, can make a poorly made telescope look good. That's not casting any aspersions on your craftmanship, just a generalisation that it will offer a significant improvement in pointing accuracy in just about every case. Gary can be very proud of the achievement he has made in putting something as complex, revolutionary and beneficial as TPAS, in the hands of amateur astronomers at a bargain price. It is important that you understand the "basic" operations and setup of Argo Navis as Gary has explained, before you start on TPAS, but my further advice to Gary's advice is to start using TPAS as soon as you think you can handle it.

I would be turning atmospheric refraction "off". If you are doing "normal" Deep Sky and Planetary observing it is not necessary to use it. Whilst it's a nice feature to have in some cases for certain specific purposes, it is not necessary in most normal observing situations. With refraction turned off and a good TPAS model established both my scopes point with an accuarcy better than 10' even very low down. The pointing errors caused by mount fabrication errors of hand made telescopes, tube and truss flexure pointing low down and mirror flop, will greatly outweigh the compensation necessary due to atmospheric refraction in 99% of situations involving hand made dobsonians. When refraction modelling is "on", as Gary explained earlier, it is important to have the date, time and observing location accurately set. If you change location and don't change the settings, with refraction "on" you can find your pointing out by a good bit. I find it far easier to turn refraction off and then I don't need to worry about changing observing locations. With refraction off, I have observed as far apart as Coonabarabran and Albury with my location remaining set at my home address on the Central Coast and had excellent pointing accuracy at all times to all parts of the sky. If I had refraction on I would have undoubtedly had to adjust the observing locations to a fairly accurate degree.

Cheers,
John B
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  #45  
Old 24-09-2008, 11:48 AM
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erick (Eric)
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This has become a very informative thread, thanks all.
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  #46  
Old 24-09-2008, 11:59 PM
gary
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Quote:
Originally Posted by ausastronomer View Post
I would be turning atmospheric refraction "off". If you are doing "normal" Deep Sky and Planetary observing it is not necessary to use it. Whilst it's a nice feature to have in some cases for certain specific purposes, it is not necessary in most normal observing situations. With refraction turned off and a good TPAS model established both my scopes point with an accuarcy better than 10' even very low down.
Hi John,

Thanks for the post.

You are absolutely correct in that most Dob owners could get by with REFRACTION
set to ON. As you are aware, refraction effects becoming larger as you near the
horizon and most Dob owners shun this part of the sky. However, we still recommend
to keep it ON as a matter of course and in particular when you perform a TPAS
run.

As it turns out, the NPAE and CA terms are hard to distinguish unless you
take a reasonable number of samples spread over the sky but in particular
having a good spread in Altitude, from near the zenith down to the horizon.
As the effects of refraction can be extremely significant near the horizon, it
is important for the TPAS analysis that REFRACTION be switched to ON.

Best Regards

Gary
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  #47  
Old 25-09-2008, 03:43 AM
ausastronomer (John Bambury)
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Hi Gary,

I guess I am a relic from the prehistoric (pre TPAS) times. I think I recall your advice at some time in the distant past that I should turn refraction "OFF". So I have continued to do that over many years.

TPAS has changed a lot of things, all for the better, so I will remember to turn it on in future and accurately set the date, time and location parameters.

I guess it shows I don't point the scope down near the trees all that often

Cheers,
John B
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  #48  
Old 28-09-2008, 05:44 PM
CoombellKid
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Gary and John,

Thanks for the tips guys. Sorry I haven't been back in here to reply. Too
busy sleeping, observing and parenting. I found a couple of factors in my
pointing accuracy. Firstly the rubber mats on the wet clay earth we have
here in Coombell was a major part. I've removed the mats and the ground
has pretty much dried out since the first couple of outings. I last few nights
the porblem has all but disapated 99% of the objects land in the FOV of my
14mm XW no matter what area of sky to point at, mostly in the center. I
still I reckon I'll should look at laying a slab I think.

Still took all of what you guys said. And John yeah mate! I took up woodwork
again since high school nearly 30 years ago late last year when I built the lil 8"
truss dob for my boy's, And although I did take my time and tripple checked
my measurements even remaking bits that I didn't feel happy with. I looked
at the project more as an engineering problem with cosmetics coming in
second. Still I think it can be sweaten more with TPAS. The system does
have an estimated 3 arcmins backlash about 10% of the FOV of a 14mm XW
which is 32 arcmins. However in saying that you have no problem placing
objects in the center of FOV. Also the dobson hole effect is rather minimal
you can scan around up near the zenith with relative ease.

Gary, I'll have the measurements for the encoder cables when.... ummm
I stop using the scope long enough to take them lol

Anyways thanks for the help guys

regards,CS
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  #49  
Old 30-09-2008, 05:00 AM
CoombellKid
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FWIW, a backlash I gave above of 3 arcmins was rather generous. It is
actually around 40 arcsecs or about the width of Jupiter.

regards,CS
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  #50  
Old 30-09-2008, 11:28 AM
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Starkler (Geoff)
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Rob if you are using 10,000 step encoders which are the norm these days, you have a pointing resolution of 2.16 arcmin per encoder step.
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  #51  
Old 30-09-2008, 01:30 PM
CoombellKid
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Geoff,

Quote:
Originally Posted by Starkler View Post
Rob if you are using 10,000 step encoders which are the norm these days, you have a pointing resolution of 2.16 arcmin per encoder step.
Yup I have and Yup I knew that. You only notice the backlash when your
scanning around at the eyepiece but even then at around 40 arcmins it is
nothing. I think you will see some in any truss dob.

I know I have a mount error which puts the pointing accuracy out by about
16 arcmins on a 180 degree spread, TPAS run should fix this. However on
saying that the two people so far who have tried my scope didn't pick it up.

All 'n' all I'm pretty happy with the results of the build as well as the
performance of the Argo Navis, both have been a real pleasure to use. I
look forward to the next one

regards,CS
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  #52  
Old 01-10-2008, 02:18 AM
redsquash
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Agos navis or Killer eyepieces and scope

I am in a slight dilema.
I just bought a vixen Porta Mount with a Vixen reflector 130mm f/5 telescope, to start this hobby.

If I bought a Agos Navis would I be making the best use of my funds. I could buy a good 2nd hand scope or killer eyepices if I didnt buy the AN.

Somewhere down the track I will probably by a goto /push to set up, but now I know I cant afford to do both.

How useful would the Agos navi be on my minor Grab and go scope? Most people seem to have at least an 8 inch or 10 inch scope ?
SO I am not sure which direction will be the more productive, though I believe , either option will produce good results.
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  #53  
Old 01-10-2008, 05:56 PM
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Kevnool (Kev)
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Quote:
Originally Posted by redsquash View Post
I am in a slight dilema.
I just bought a vixen Porta Mount with a Vixen reflector 130mm f/5 telescope, to start this hobby.

If I bought a Agos Navis would I be making the best use of my funds. I could buy a good 2nd hand scope or killer eyepices if I didnt buy the AN.

Somewhere down the track I will probably by a goto /push to set up, but now I know I cant afford to do both.

How useful would the Agos navi be on my minor Grab and go scope? Most people seem to have at least an 8 inch or 10 inch scope ?
SO I am not sure which direction will be the more productive, though I believe , either option will produce good results.

It would depend on if you ever want to read star charts again

All the charts do now is give us a list to view ....cheers Kev.
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  #54  
Old 02-10-2008, 04:04 PM
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gary or anyone can I retro fit an argo to my homebrew truss dob ?
I'm thinking i should get one after messing around with robs the other night

I'm not sure about my large alt bearings though
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  #55  
Old 02-10-2008, 04:57 PM
CoombellKid
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Quote:
Originally Posted by nightstalker View Post
gary or anyone can I retro fit an argo to my homebrew truss dob ?
I'm thinking i should get one after messing around with robs the other night

I'm not sure about my large alt bearings though
I dont think you should have too much trouble Graham. 15" obsession kit
is the smallest they make (as far as I'm aware) for Kriege style truss dobs.
The kit might be a bit big for your scope, How big are your Alt bearings?
is the center of rotation at the top of the mirror box?

I have the Obsession 15" kit on my scope and the Alt tangent arm is 360mm
and my Alt bearings a 23"

In anycase I'm sure Gary will be able to help with more info

regards,CS
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  #56  
Old 02-10-2008, 07:33 PM
gary
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Arrow

Quote:
Originally Posted by nightstalker View Post
gary or anyone can I retro fit an argo to my homebrew truss dob ?
I'm thinking i should get one after messing around with robs the other night

I'm not sure about my large alt bearings though
Hi Graham,

Thanks for the post.

Indeed, retro-fitting Argo Navis systems to home-built telescopes is popular
and if you email me at sales@wildcard-innovations.com.au I would be
happy to provide some obligation-free advice.

Often it is possible to improvise one of the off-the-shelf kits. As Rob mentioned,
the kit used on the Obsession that we stock is a popular choice.

We also have some in-house machining capability here in Sydney and can
fabricate custom components on demand, such as encoder ready Az pivot bolts
and Alt encoder couplings, all at reasonable rates.

We might be able to recommend something suitable if you could let
me know by email the following -

1) The aperture of the primary
2) The type of Alt bearing employed (i.e. full filled-in circle, filled-in semi-circle, non-filled-in semi-circle with/without crossbar, etc).

For the Az axis, please let me know the following dimensions -
1) The thickness of the ground board.
2) The thickness of the base of the rocker.
3) The dimension of the gap between the top of the ground board and the rocker.
4) The dimensions of the current Az pivot bolt.
5) The dimension of the gap of the edge of the mirror box to the inside of the rocker as it passes over where the Az pivot bolt is.

Some photos of the scope can be useful.
Once we have this information, we can supply more specific suggestions.

Best Regards

Gary Kopff
Managing Director
Wildcard Innovations Pty. Ltd.
20 Kilmory Place, Mount Kuring-Gai
NSW. 2080. Australia
Phone +61-2-9457-9049
Phone +61-2-9457-9593
sales@wildcard-innovations.com.au
http://www.wildcard-innovations.com.au
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  #57  
Old 02-10-2008, 08:52 PM
redsquash
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Quote:
Originally Posted by Kevnool View Post
It would depend on if you ever want to read star charts again

All the charts do now is give us a list to view ....cheers Kev.
Hi kev,
It sounds like the funds should not go to killer eyepieces or other gear, since my aim is to enjoy the stars, rather than enjoy reading a map to find the stars!

Thats a lot of cash to tie up in a small scope .....?
I hate watching the moths fly from my wallet but if the benefit is really there,I don't mind spending the cash .
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  #58  
Old 02-10-2008, 10:31 PM
gary
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Quote:
Originally Posted by redsquash View Post
How useful would the Agos navi be on my minor Grab and go scope? Most people seem to have at least an 8 inch or 10 inch scope ?
SO I am not sure which direction will be the more productive, though I believe , either option will produce good results.
Hi,

Argo Navis installations on "grab and go" scopes are popular, including on mounts
such as the Tele Vue's, Giro 2's, Discmounts, various binocular mounts and the like.
Many users are using these mounts with modest aperture scopes, such as
small refractors. For example see here -
http://www.wildcard-innovations.com....alec_dunn1.jpg and here -
http://www.wildcard-innovations.com....ick_altaz1.jpg

The motivations of fitting a system to a grab and go scope are essentially identical
to fitting it to larger aperture scopes, namely, helping the user "find more stuff".

Many owners are using their Argo Navis systems on telescopes in heavily
light polluted urban environments and the ability to "find stuff" more easily,
despite these less than optimal observing conditions, means they can
can get the most out of their observing session. For many, work, family and
other time commitments means every minute spent at the eyepiece is
precious time. For these people, an Argo Navis effectively buys them time.

Best regards

Gary Kopff
Wildcard Innovations Pty Ltd
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  #59  
Old 03-10-2008, 12:52 PM
CoombellKid
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Quote:
Originally Posted by Kevnool View Post
All the charts do now is give us a list to view ....cheers Kev.
what an excellent and simple idea, Starry Night still has a use after all.

regards,CS
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  #60  
Old 03-10-2008, 02:27 PM
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Starkler (Geoff)
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Quote:
Originally Posted by Kevnool View Post
It would depend on if you ever want to read star charts again

All the charts do now is give us a list to view ....cheers Kev.
Charts still have their uses.

eg1. You use the AN to find a faint galaxy and you can see more than one in the fov. Which is which?

eg2. The AN reads 0.0 0.0 but you cant see anything. Where is it? Am I really in the right place? Which of those stars in the fov is that tiny Abell planetary?
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