Help with MiniDob Mount -

[Perene]

https://dl.dropboxusercontent.com/u/53143167/Instruction_Manual_-_MiniDob_Mount_-_Maksutov_90mm.pdf

About page 5 from this manual, I was instructed by the store where I purchased the Mak 90 to (before using Stellarium with their drivers to control the mount, GO-TO) point the telescope to True North and take into consideration my magnetic declination (?). The problem is that I don't know anything about this procedure, and so far it remains the only step from this manual that I don't know how to do it exactly.

I found this website:

http://magnetic-declination.com/what-is-magnetic-declination.php

Which says something like this:

RECIFE PERNAMBUCO (my location)
Latitude: 8° 3' 14" S
Longitude: 34° 52' 52" W
Magnetic declination: -22° 16' WEST
Declination is NEGATIVE
Inclination: -28° 19'
Magnetic field strength: 25880.2 nT

The translated version from this manual (in portuguese): https://dl.dropboxusercontent.com/u/53143167/Manual_-_Maksutov_90mm.pdf

Also mentions something like this, but it doesn't mention anything about South. They say I should always point to North:

*********

Loosen the azimuth clutch knob and the altitude clutch knob, point the telescope tube to Polaris (For northern hemisphere usage) or South Pole (For southern hemisphere usage). Then lock the clutches again...

*********

I have also saw this picture among others in the translated version...

Can someone please help me with this thing?

[Cornelius Varley]

You should ignore the instructions for setting up the mount in the northern hemisphere, just follow the information for setting up the mount in the southern hemisphere.

[Perene]

You should ignore the instructions for setting up the mount in the northern hemisphere, just follow the information for setting up the mount in the southern hemisphere.

OK, but this is what I don't understand - the alignment itself.

This is the mount:

Pic 1_A, altitude adjustment: http://i.imgur.com/xqr8T04.jpg

Pic 1-B: http://i.imgur.com/0UV7omC.jpg

Pic 2: http://i.imgur.com/cGSAq1s.jpg

Azimuth clutch knob...

Now take a look into these 2 last pics:

http://i.imgur.com/CWado5W.jpg

And...

http://i.imgur.com/GJUEtqX.jpg

The mini-compass that came with the Red Dot can be seen above the telescope.

What I don't understand is how should I move the mount itself to north for example, then move again 22 degrees to west. This 2nd adjustment is for the True (not magnetic) North.

What I don't know is how to move the mount. Where to put the mini (or perhaps another?) compass, how to move 22 degrees to west after that...

For the 2nd adjustment, do I need a protractor? *

*  A rectangular, square, circular or semicircular measuring instrument, typically made of transparent plastic or glass, for measuring angles. They are used for a variety of mechanical and engineering-related applications, but perhaps the most common use is in geometry lessons in schools.

Both manuals are just telling me to make an alignment, but they don't explain how to do it when you are touching the mount.

And I need a correct alignment to avoid errors when testing with Stellarium and a GO-TO driver to point to different celestial bodies.

From the pictures I posted above, you can see I am just moving the mount/tube without 100% accuracy. For example, even if I draw a line in the ground from where the magnetic North from that mini-compass is, how do I know the tube is pointing to the center of that line? Where in that mount should I look to make sure of that? Perhaps this area?

[ronin]

If you can point the scope true North or South then you do not need the magnetic declination.

Magnetic declination is what you have to adjust the direction obtained by a magnetic compoass by to get the scope to point true North if you use a magnetic compass to start at magnetic North.

Something like True N =  Mag N +/- Mag Dec

You want true North/South.

So if you can set to that you do not need the magnetic declination.

If the store said: "point the telescope to True North and take into consideration my magnetic declination (?)"

Then I question what they are talking about.

If they said "Point the scope to True North by using a compass and taking into account magnetic declination." they would be right. But if you can point it true North/South then you do not need the magnetic declination.

As you say you have to rotate the mount about 22 degrees from what the compass says, which is a hell of a lot.

I doubt that the compass that came with the scope allows for this. You would want a compass intended for trekking where there is a rotating bezel on it. You rotate the bezel so that 22 degrees is where the magnetic compass is then 0 on the bezel is true N/S - well thats the theory.

Equally at that difference you can use magnetic N/S and then look at the sky for true N/S and simply rotate the mount in the required direction. It is getting a fairly accurate 22 degrees that will be the problem. I am have a problem visualising why the adjustment is 22 degrees, just seems more then I would have expected.

Do you have a smart phone with GPS on it?  I think they will use the satallite system to define true N/S and that should be a better option.

[AndyWB]

Yeah, 22 degrees is quite possible - and looks about right for eastern Brazil.

 

And yes, I'd use a trekking compass with an adjustable bezel. If you're going to use the built in one, though, i think you need to align the scope so the compass reads 22 degrees, rather than North, but I'm not entirely sure if it's 22 degrees to the east, or 22 degrees to the west. I think it might be 22 degrees to the east of north.

My reasoning is that the built in compass is a cheapish one, and doesn't have an adjustable bezel to compensate for magnetic declination, so you'll have to do it yourself. I get confused about the switch to the southern hemisphere, too, though, so I'm not sure which side of North you need.

[Perene]

Even though the store said I should always point to North, based on my coordinates that is incorrect and I am in the Southern Hemisphere, right? Because Polaris can't be seen in my location (based on Stellarium), while Sigma Octantis is clearly visible.

Polaris: http://i.imgur.com/WO9d5xB.png (invisible no matter what)

Sigma Octantis: http://i.imgur.com/0ON12o1.png

Does this fact alone tells me I should point the telescope tube to South Pole instead of North?

Now, about the "point the telescope tube" part, I don't get it. Even if I find another compass, I still need to know how to move the telescope tube properly. If it's a very precise adjustment I can't just move the telescope tube to whatever my calculations are tellling me to.

Should I determine the position first and then move the mount in a way that the line from my calculations is facing this part of the mount?



Or perhaps the telescope tube can be moved aimlessly to where the calculation is going?