Argo Navis - Any tips on getting 90 degree aligment

[Eric48]

Has anyone any tips on how to work out whether the OTA on a dob mount is at 90 degrees to the base? Do I ensure the base is horizontal using a spirit level and then use the spirit level on the OTA's dust cap to see if it is horizontal too? And then somehow put some kind of a stop in between the OTA and the dob mount to set it at 90 degrees? I have to move my 12 inch dob around quite a bit on a trolley depending on which bit of sky I want to look at - lots of trees on the small farm where I observe (but wonderful dark skies).

Eric

[erick (Eric)]

For the Argo Navis, don't worrry. The clever little beastie works it out for itself. Plonk the base down - doesn't matter if it is not really level, plonk the OTA on the base and push it to the vertical stop - doesn't matter it it is not really vertical. Fix Alt Ref with auto adjust on, Align star and away you go. Obviously Align each time you set up the dob, even in the same location.

I though the same when I started.

[jakob]

I move my dob to the the top position until it hits the back vertical board on the base. I then measure the amount of out of square to the base and enter that figure into the Argo.
I my case:
setup alt ref/alt ref=+92.700 ( my end stop is past 90deg by 2.7 deg)

Now all I do, push the Tube to the stop and
mode fix alt ref/enter/enter/exit

I hope this will help.
Regards J.

ps.
You can use the Argo to give you this angle. Next time when you are aligned, set the argo to mode az alt, push the tube to the top stop and read the alt angle of the display!

[Eric48]

Thanks Jakob and Eric - simple when you know how. Just out of interest Jakob what do you use to mechanically measure how far out of 90 your dob is when you push it against the backboard of the mount?

Eric

[erick (Eric)]

Promise you, don't worry about a perfectly horizontal base and perfectly vertical OTA. Look at post #3 in:-

http://www.iceinspace.com.au/forum/s...=35708&page=14

[astroron (Ron)]

Originally Posted by erick

Promise you, don't worry about a perfectly horizontal base and perfectly vertical OTA. Look at post #3 in:-

http://www.iceinspace.com.au/forum/s...=35708&page=14

Eric is right I took my 16"scope all the way to Western Australia
Set up at the WA Dark Sky site at Tammin on the Great Eastern Highway, did not change the location,just the time, I am not sure if that was even necessary.
Did my Two Star Alignment in the ARGO NAVIS and was observing as if I had never left home in no time at all

[Eric48]

Thanks Eric for your later post plus the link to Gary's post - feel relieved.

I bought an illuminated reticle eyepiece just so I could be sure I was centering my 2 stars dead on but then started to worry about the initial 90 degree alignment. Will put your advice into practice on the weekend. Haven't really given my argo navis set up much of a test after buying it sometime ago but not being able to get back to observing until very recently.

Eric

[erick (Eric)]

I also bought and used an illuminated crosshair eyepiece to align - then got lazy and just centred by eye in a widefield eyepiece - result was good enough for me! But I am usually looking for targets that are readily spotted as long as you can get them into a 27mm or 35mm eyepiece field.

[gary]

Originally Posted by Eric48

Has anyone any tips on how to work out whether the OTA on a dob mount is at 90 degrees to the base?

Eric

Thanks to Erick for posting the link to this post I made that describes the
AUTO ADJUST ON feature -
http://www.iceinspace.com.au/forum/s...47&postcount=3

Originally Posted by Eric48

Do I ensure the base is horizontal using a spirit level and then use the spirit level on the OTA's dust cap to see if it is horizontal too?

Put the spirit level away. There is absolutely no need to level
the mount to use the system.

By way of further background, the encoders are what are known as incremental
encoders. When you power them on, they have no inherent zero reference point.

As it turns out, one only needs to determine a reference point for the Alt encoder.
The AUTO ADJUST features takes the sting out of establishing this.
One only need push the scope roughly to the point where the optical axis of
the scope is parallel to the Az axis, with the OTA pointing upwards. Typically
with a Dob if you push the OTA toward the vertical in Alt, most Dobs only allow
you to push the OTA so far before it hits the vertical board in the rocker box.
This might not be exactly the 90 degree point, it might be, say, 88.123 or
93.456. It matters not. If one then performs a FIX ALT REF 90 degree step
with AUTO ADJUST ON and then goes on to perform a two star alignment,
AUTO ADJUST ON will refine your initial 'hint' as to what the ALT REF point is
and compute it on the basis of the star alignment itself.

Thank you to all others who kindly responded.

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

[Eric48]

Thanks Gary (& Eric) - now really looking forward to putting the argo navis into action this weekend - but will use the illuminated crosswire eyepiece for the 2 star alignment - it's a very nice piece of Vixen kit - almost tempts me to take up astrophotography just to put it to its usual use - but then I'd be on the road to financial ruin with tracking mounts and expensive cameras etc.

Eric