•

# Losmandy Gemini gurus....

This topic has been archived. This means that you cannot reply to this topic.
21 replies to this topic

### #1 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 28 March 2009 - 09:42 PM

Dear Cloudynighters....
I have a quick one...

When doing the "additional aligns" on Gemini,
if I get an offset from Polaris of "A:11' E:3'", how far is this? should I care about this?

### #2 Doug Sanqunetti

Doug Sanqunetti

Mariner 2

• Posts: 211
• Joined: 19 Dec 2005

Posted 29 March 2009 - 07:57 AM

According to the manual:

Gemini will display the calculated offset from the pole in arcseconds in azimuth(A) and elevation (E). For example, it might display "A:+15 E:-10" to indicate that your mount is 15 arcseconds from the pole in azimuth and 10 arcseconds from the pole in elevation.

Whether you should care or not depends on what you are trying to do. If I was trying to take images, I would want these numbers to be relatively small.

Best Regards, Doug

### #3 Charlie Hein

Charlie Hein

Voyager 1

• Posts: 12482
• Joined: 02 Nov 2003

Posted 29 March 2009 - 08:00 AM

Joselo, are you trying to do an "additional align" on Polaris itself?

### #4 lineman_16735

lineman_16735

Tak-o-holic

• Posts: 3118
• Joined: 04 Dec 2004

Posted 29 March 2009 - 09:34 AM

IIRC these numbers are in arc minutes not arc seconds.

### #5 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 29 March 2009 - 10:30 AM

Does this mean that "A:11' E:3'"
means that the true NCP is actually
11 arcmins EAST
3 arcmins NORTH
from my actual alignment?

### #6 Doug Sanqunetti

Doug Sanqunetti

Mariner 2

• Posts: 211
• Joined: 19 Dec 2005

Posted 29 March 2009 - 11:34 AM

Chris,

The Gemini manual from April 2006 says this value is in arcseconds. Page 21 4th paragraph down.

I quoted directly from the manual in my post above. I suppose it is possible that the manual is incorrect.

Best Regards, Doug

### #7 Doug Sanqunetti

Doug Sanqunetti

Mariner 2

• Posts: 211
• Joined: 19 Dec 2005

Posted 29 March 2009 - 11:40 AM

These numbers tell you that your mount's RA axis is misaligned from the pole by the amounts given. Most of the time you really don't care about these values. If you are a visual observer, Gemini will use the calculated values when you do a goto operation so that it can center objects in the field of view. If you are doing Astrophotography, you will want these values to be relatively small to avoid field rotation on long exposures especially with long focal length scopes. On short exposures or with short focal lenghth scopes, this becomes less important. You will probably never get these values to be zero.

Best Regards, Doug

### #8 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 29 March 2009 - 02:27 PM

Chris,
you are correct. the values are in Arcseconds.

Doug- does this mean that I need to move the axis on 13 arcsecs EAST, and the Elevation 3 arcsecs NORTH?

I guess this will be pretty tough to get closer than it already is.

I mean, we are talking about arcsecs.

### #9 Charlie Hein

Charlie Hein

Voyager 1

• Posts: 12482
• Joined: 02 Nov 2003

Posted 29 March 2009 - 02:52 PM

Chris,
you are correct. the values are in Arcseconds.

Doug- does this mean that I need to move the axis on 13 arcsecs EAST, and the Elevation 3 arcsecs NORTH?

I guess this will be pretty tough to get closer than it already is.

I mean, we are talking about arcsecs.

If you have a permanent installation I would definitely remove as much error as I possibly could. If it's a mobile installation it's your call to make the error smaller than that. Depending on the focal length you're shooting at and the length of your subs you probably won't see much of an issue. You might want to try out the polar alignment assist - it can really get you pretty darn close if you're careful.

### #10 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 29 March 2009 - 03:58 PM

Hi Charlie,
I do have a permanent pier...
and I am really interested in getting as close as possible to the NCP.

### #11 lineman_16735

lineman_16735

Tak-o-holic

• Posts: 3118
• Joined: 04 Dec 2004

Posted 29 March 2009 - 06:34 PM

The gemini manual on page 44 says all the mount modeling parameters are given in minutes of arc. So you are indeed off by arc minutes and not arc seconds.

### #12 lineman_16735

lineman_16735

Tak-o-holic

• Posts: 3118
• Joined: 04 Dec 2004

Posted 29 March 2009 - 06:37 PM

The manual does indeed say on page 21 arc seconds. This is incorrect though, as discussed on the Losmandy group a while ago.

### #13 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 29 March 2009 - 06:37 PM

well something is wrong.
page 21 on my manual says arcseconds ....

?

### #14 lineman_16735

lineman_16735

Tak-o-holic

• Posts: 3118
• Joined: 04 Dec 2004

Posted 29 March 2009 - 07:27 PM

I agree but I'm sure arcseconds is a misprint. If it where arcseconds what would Gemini display if you were 2 arc minutes off the pole? 120"? For most imaging 2 arcminutes within the pole is plenty fine enough. My permanent mount is within 20 arcseconds but that took some time to accomplish. How did you do your polar alignment? If only with the polar scope I can say that you will only get within an arcminute by pure luck. Shoot Rene an e-mail about this.

### #15 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 29 March 2009 - 07:42 PM

Chris,
it could be a misprint. talking about arcseconds is pretty darn close to the pole. I send Rene an email.

### #16 lineman_16735

lineman_16735

Tak-o-holic

• Posts: 3118
• Joined: 04 Dec 2004

Posted 29 March 2009 - 07:46 PM

I just sent Rene an e-mail as well. I could be wrong but I could swear that on the Losmandy yahoo group this came up a year or two ago and at that time it was agreed that arcminutes was the correct measure. Hopefully Rene will respond.

### #17 Charlie Hein

Charlie Hein

Voyager 1

• Posts: 12482
• Joined: 02 Nov 2003

Posted 29 March 2009 - 11:01 PM

Since you have a permanent installation then it's best just to do an old fashioned drift alignment until you have eliminated as much error as possible. If you can do 20 minutes you should be fine.

### #18 lineman_16735

lineman_16735

Tak-o-holic

• Posts: 3118
• Joined: 04 Dec 2004

Posted 30 March 2009 - 05:56 AM

I received a response from Rene. The values given on the hand controller are indeed in minutes of arc. Renee, also goes on to explain that the calculations are done in arcseconds which can be displayed through Gemini Control Center which is a software package for the Gemini System.

### #19 rsbfoto

rsbfoto

Messenger

• Posts: 450
• Joined: 10 Jun 2006

Posted 30 March 2009 - 01:54 PM

HI,

There is a free program with which you can read your misalignment in Arcseconds and that one is GRS from Paul Kanevsky and you can find it here

GRS

regards Rainer

### #20 rsbfoto

rsbfoto

Messenger

• Posts: 450
• Joined: 10 Jun 2006

Posted 30 March 2009 - 06:12 PM

Does this mean that "A:11' E:3'"
means that the true NCP is actually
11 arcmins EAST
3 arcmins NORTH
from my actual alignment?

Hi,

Your A:11 value means you are WEST (fron of Telescope) and have to move the front of the Telescope to the EAST

The E:3 means you are too Low and you have to rise the front of your telescope.

If you have negative values then accordingly to the other side eg. A:-XX move the front of the scope to the West and E:-XX then lower the front of the telescope.

All this always seen from the backside of the mount eg. looking North.

I would not worry at the moment with the E:3 value but I would try to get a lower value for A:XX

If you are below >3 in both axis you are very good aligned. Of course it is possible to get it lower and it all depends as others said what you are doing be it visual or photography

regards Rainer

### #21 Joselo

Joselo

Viking 1

• topic starter
• Posts: 544
• Joined: 26 Feb 2008

Posted 30 March 2009 - 09:30 PM

Hi Rainer,
thank you for your time to explain. I have seen your posts on the yahoo group. how is your upgrade going??

### #22 rsbfoto

rsbfoto

Messenger

• Posts: 450
• Joined: 10 Jun 2006

Posted 31 March 2009 - 11:48 AM

Hi Rainer,
thank you for your time to explain. I have seen your posts on the yahoo group. how is your upgrade going??

You are welcome. Great results

## CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

 Cloudy Nights LLC Cloudy Nights Sponsor: Astronomics