Telescope Reviews: Losmandy Gemini gurus....

· Get a Cloudy Nights T-Shirt

· Submit a Review / Article

Click here if you are having trouble logging into the forums

Privacy Policy | Please read our Terms of Service | Signup and Troubleshooting FAQ | Problems? PM a Red or a Green Gu… uh, User

You are not logged in. [Login]

Entrance · Main Index · Search · New user · Who's Online
FAQ · Calendar

Equipment Discussions >> Mounts

Pages: 1 | 2 | (show all)

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Losmandy Gemini gurus....
#3010852 - 03/28/09 10:42 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?

Post Extras:

Doug Sanqunetti
sage

Reged: 12/19/05

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3011309 - 03/29/09 08:57 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

Post Extras:

Charlie Hein
Postmaster

Reged: 11/02/03

Loc: 26.06.08N, +80.23.08W

Re: Losmandy Gemini gurus.... new

[Re: Doug Sanqunetti]
#3011316 - 03/29/09 09:00 AM

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

Post Extras:

lineman_16735
Tak-o-holic

Reged: 12/04/04

Loc: Central PA

Re: Losmandy Gemini gurus.... new

[Re: Doug Sanqunetti]
#3011466 - 03/29/09 10:34 AM

IIRC these numbers are in arc minutes not arc seconds.

Post Extras:

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3011581 - 03/29/09 11:30 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?

Post Extras:

Doug Sanqunetti
sage

Reged: 12/19/05

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3011726 - 03/29/09 12:34 PM

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

Post Extras:

Doug Sanqunetti
sage

Reged: 12/19/05

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3011750 - 03/29/09 12:40 PM

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

Post Extras:

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Re: Losmandy Gemini gurus.... new

[Re: Doug Sanqunetti]
#3012103 - 03/29/09 03:27 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.

Post Extras:

Charlie Hein
Postmaster

Reged: 11/02/03

Loc: 26.06.08N, +80.23.08W

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3012157 - 03/29/09 03:52 PM

Quote:

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.

Post Extras:

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Re: Losmandy Gemini gurus.... new

[Re: Charlie Hein]
#3012297 - 03/29/09 04:58 PM

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

Post Extras:

lineman_16735
Tak-o-holic

Reged: 12/04/04

Loc: Central PA

Re: Losmandy Gemini gurus.... new

[Re: Doug Sanqunetti]
#3012628 - 03/29/09 07:34 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.

Post Extras:

lineman_16735
Tak-o-holic

Reged: 12/04/04

Loc: Central PA

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3012635 - 03/29/09 07:37 PM

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

Post Extras:

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3012637 - 03/29/09 07:37 PM

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

?

Post Extras:

lineman_16735
Tak-o-holic

Reged: 12/04/04

Loc: Central PA

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3012741 - 03/29/09 08:27 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.

Post Extras:

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3012765 - 03/29/09 08:42 PM

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

Post Extras:

lineman_16735
Tak-o-holic

Reged: 12/04/04

Loc: Central PA

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3012773 - 03/29/09 08:46 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.

Post Extras:

Charlie Hein
Postmaster

Reged: 11/02/03

Loc: 26.06.08N, +80.23.08W

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3013147 - 03/30/09 12:01 AM

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.

Post Extras:

lineman_16735
Tak-o-holic

Reged: 12/04/04

Loc: Central PA

Re: Losmandy Gemini gurus.... new

[Re: Charlie Hein]
#3013458 - 03/30/09 06:56 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.

Post Extras:

rsbfoto
sage

Reged: 06/10/06

Re: Losmandy Gemini gurus.... new

[Re: lineman_16735]
#3014167 - 03/30/09 02:54 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

Post Extras:

rsbfoto
sage

Reged: 06/10/06

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3014658 - 03/30/09 07:12 PM

Quote:

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

Post Extras:

Joselo
professor emeritus

Reged: 02/26/08

Loc: Texas

Re: Losmandy Gemini gurus.... new

[Re: rsbfoto]
#3015029 - 03/30/09 10:30 PM

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

Post Extras:

rsbfoto
sage

Reged: 06/10/06

Re: Losmandy Gemini gurus.... new

[Re: Joselo]
#3016015 - 03/31/09 12:48 PM

Quote:

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

Post Extras:

Pages: 1 | 2 | (show all)

Extra information

16 registered and 22 anonymous users are browsing this forum.

Moderator: Bowmoreman, bilgebay, iceblaze

Print Thread

Forum Permissions
      You cannot start new topics
      You cannot reply to topics
      HTML is disabled
      UBBCode is enabled

Thread views: 860

Jump to

CN Forums

Home

Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics