TAK EM200 Alignment Question

[Pago Cruiser]

Hi,

First post here, so be nice...

This post is probably specific to any Tak EM200 owners...

Just took delivery on a Takahashi EM200, and am having a devil of a time with what is laughingly called the instruction manual. Finally got most of it figured out, but I'm struggling with the "Polar Alignment By The Equator" section.

I'm at Latitude 14.2S, and while I can interpolate data in the manual (page 24), and arrive at refraction error correction value of about 4' 12", I cannot for the life of me figure out how to implement this value in the reticle offset.

I've posted this on the Cloudy Nights forum "up North" but most of those guys are hemispherically challenged...

Regards all,

Mitch

[Dennis]

Hi Mitch

I wrote a Microsoft Excel worksheet that automatically calculates the date and time for the Southern Hemisphere, as the standard Polar Alignment Scope (PAS) reticule is for the Northern Hemisphere.

That is, the as fitted PAS reticule:

• The outer “Year” circle starts at 1 (Jan) and increments clockwise (CW) to 12 (Dec).
• The inner “Time” circle starts at 0hr and increments anticlockwise (AC) to 24hrs. This is for the Northern Hemisphere.

For the Southern Hemisphere, the opposite is required, as follows:

• The “Year” circle starts at 1 (Jan) and increments anti-clockwise (AC) to 12 (Dec).
• The “Time” circle starts at 0hr and increments clockwise (CW) to 24hrs.

My MS Excel worksheet simply looks at the current system date and time on my notebook computer, and converts them to the “opposite” Northern Hemisphere values which I can then simply dial into the PAS.

So, here is how I do it:

1. For Brisbane at Longitude 152 E, I set the small off-set scale on the RA body to a value of +2, using the lower scale which I think goes from -10 through 0 to +10.
2. Rotate the RA axis until the bubble level is centered horizontally.
3. Rotate the DEC axis so that the PAS is looking through the hole in the shaft.
4. I then open my spreadsheet which then shows me the adjusted (calculated) Date and Time.
5. Date now, in Southern Hemisphere = 21/09/2006 converts to 11/04/2006 (ignore year).
6. Time now, in Southern Hemisphere = 17:55 converts to 6:05 AM (ignore seconds).
7. I then rotate the PAS at the eyepiece end so that 11th April lines up with 6:05.
8. Then, I adjust the Alt/Az screws until Sigma Octans is positioned between 2000 and 2010 at roughly 2006 in the PAS FOV.

This has given me pretty accurate polar alignment for good GoTo’s.

Hope that helps. If you want the spreadsheet, let me know and I’ll e-mail you a copy.

Cheers

Dennis

[74tuc]

Hi Mitch,

Takahashi seem to neglect the people in the Southern Hemisphere.

The EM200 manual shows how to correct for refraction in Northern hemisphere only and then that is pretty vague. For southern polar alignment there is no offset on the graticle to take into account refraction. If you place sigma-Oct as close as you can to 2007 (not 2006) on the southern hemisphere line you will find that your polar alignment is "not too bad" for most uses. Accurate polar alignment can then be done by drift alignment.

Good luck.

74Tuc