3 star alignment help

[Subaru19]

Hi all, I have a question about 3 star alignment on heq5 pro and hopefully you will be able to help me. After polar aligning my mount, i choose 3 star alignment and i generally try to go for stars in the west and south-west part of the sky, as that's where i have the most visibility. Choosing the first 2 stars is not a big problem, but the options ( only about 10)  that the synscan controller gives for the 3rd star are not viewable from my position.  i dont understand why it doesnt give me the option to choose from loads of other bright stars that are right up there in front of me. For example, the usual 1st and 2nd stars are alioth, alkaid and arcturus. The third star is something i can't slew to because of obstruction from buildings, such as vega, alpheratz, rukbah, and so many others that are on the east. This is frustrating as my enthusiasm quickly evaporates by the time i get to the third star as i have to keep repeating the process, selecting different 1st and 2nd stars in the hope that the 3rd star would be a viewable one. is this what normally happens or is there something i am not doing right. Thanks for your advice

[jeffwjz]

I'm using Heq5 pro as well and I'm always using two star alignment. And I think two star alignment is sufficient. I tried single star alignment before and noticed from PHD tracking log that the RA axis is deviating more than DEC, so using two star alignment will adjust the performance of RA tracking. 

I believe in case of three star alignment, the third star is for fixing misalignment of telescope and mount (I forgot the terminology), for example when telescope is tilted on mount. 

I read somewhere else that alignment with third star will sometimes add additional inaccuracies. 

I don't think three star alignment is necessary if you set up your equipment correctly. Have you tried to see the mount's performance in case of two star alignment? Or any reason that you have to use three star alignment? Thanks. 

[jeffwjz]

Also if your still have Heq5 pro manual I'm sure there is a paragraph in there, detailing the purpose of single, two or three star alignment. From what I remembered, three star alignment is optional. 

[dph1nm]

16 minutes ago, jeffwjz said:

I tried single star alignment before and noticed from PHD tracking log that the RA axis is deviating more than DEC, so using two star alignment will adjust the performance of RA tracking. 

The star alignment (which is just a software model for the GOTOs) does not really affect the tracking - this is just a mechanical property of the mount (and polar alignment).

If you don't have much cone error (optical axis of telescope not aligned to the mount's rotation axis) then two star alignment should produce reasonable GOTOs.

NIgelM

Edited July 3, 2019 by dph1nm

[Cornelius Varley]

Two star alignment is usually adequate for most purposes Three star alignment is used for eliminating core error. Other stars can be selected other than the first provided by using the scroll keys at the bottom of the keypad.

[Subaru19]

Thanks everyone. will give it a go with just 2 star alignment. In answer to Cornelius' post, yes i do scroll down to select other stars, but there is only about 10 to 15 in the list and almost none of them will be in view, without being hidden behind obstructions

[Subaru19]

hello all, i tried 2 start alignment on a couple of sessions and am glad to say that it had worked. thank you all.

[Phillips6549]

Subaru

I've noticed that sometimes the selection of stars shown even for a 2 star alignment is very meagre and often unviewable in badly light polluted skies.  However, you can tell the system to offer you a full list of stars instead so you can pick your favourites or, at least, those which are visible.  In my manual (attached) it's on page 29.

Hope this helps.

Clear skies

Mark.

Synscan_V4_Hand_Control_Manual_SSHCV4-F-161208V1-EN.pdf

[Geoff Lister]

I use Synscan's "Brightest Star" alignment on my Az/Alt Skymax and Skyliner mounts. This gives me 2-star or planet + 2-star alignment. I found that the Synscan star suggestions, particularly for the 2nd star, were behind houses, fences or trees. So, I spent some time with Stellarium, and produced a table of 14 bright stars, visible from my garden, and, setting time and date for dusk (bright stars only visible to naked eye) at the middle of each month of the year, chose 3, 4, or 5 with sensible azimuth and elevation separation and noted their rough compass direction (N, NW, W etc.) and altitude. I repeated the process for 1 hour before dawn - not much use except around winter. Currently, if I power up, with the OTA horizontal and facing north, I only need to be able to see Jupiter and the automatic slew for the 2 stars (mid-July using Vega & Arcturus) gets them in the finder, or, quite often, in the FOV of a 32mm EP.

It should be possible to do something similar for an EQ mount.

Geoff