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AZ-GTI in EQ mode on SW latitude wedge base

Mount Astrophotography EQ
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#1 gofins72

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Posted 06 March 2021 - 11:31 PM

I purchased this as a grab n go/ travel rig I am putting together. I’ve read posts in this forum and have watched YouTube videos, but must be missing something or I’m confused!

I assume the home position is scope up, counter-weight down- not to either side. When I set the latitude scale on the SW base to my location, let’s say 26, the scope, when mounted,  would be pointing up way too far- far above Polaris. It’s almost as if I subtracted 26 from 90 and put the scale on the 64 mark, it’s generally pointed at the correct angle. I don’t think I have anything upside down or backwards.
Am I supposed to point in the general direction of Polaris and run a polar alignment routine of my choosing and ignore that scale on the wedge due to how I’m using the mount in EQ rather than az-alt?

I know there are quite a few on CN’s using this set-up. Thanks.


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#2 qswat72

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Posted 06 March 2021 - 11:38 PM

Do you have a picture of the scale on your wedge? I use one with the SA, and it always corresponds pretty much exactly to my latitude.

#3 gofins72

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Posted 07 March 2021 - 07:50 AM

Do you have a picture of the scale on your wedge? I use one with the SA, and it always corresponds pretty much exactly to my latitude.

So, at approximately 26.1 deg, if I attached my Redcat, it looks like it would be pointing 70-80 degrees up! I have an AVX and EQ6 set up and I can see a huge difference in the angle. I’m betting I’m completely missing something obvious and will be embarrassed by the answer! Thanks for replying. 

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#4 gofins72

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Posted 07 March 2021 - 08:09 AM

Could it be that the position in my photos is not the “home” or starting  position as with my other true EQ mounts- that home position is really with OTA on the right (or left?) I seem to remember some posts on this, but can’t seem to find them.



#5 qswat72

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Posted 07 March 2021 - 08:20 AM

I think I see what is likely happening. It’s not an issue with your wedge, but I’m pretty sure an issue with how you are aligning the mount. Looking around online the general consensus seems to be that you would point the counterweight side towards north, with the altitude text facing south. Hopefully that should work!

#6 qswat72

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Posted 07 March 2021 - 08:26 AM

Looking at it more, now I’m not so sure. Maybe someone with the mount can chime in, but it might be that you just disregard the altitude scale, or use the inverse of your latitude as you were doing.
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#7 gofins72

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Posted 07 March 2021 - 08:59 AM

I think I see what is likely happening. It’s not an issue with your wedge, but I’m pretty sure an issue with how you are aligning the mount. Looking around online the general consensus seems to be that you would point the counterweight side towards north, with the altitude text facing south. Hopefully that should work!

Yes, that’s how it is. Puzzling.


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#8 sbradley07

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Posted 07 March 2021 - 10:32 AM

Yes, that’s how it is. Puzzling.

If you look at where the wedge saddle is pointing, it's accurate from the perspective of the wedge.  Then you are adding a mount on top of that which reverses the pointing angle.  

 

You need to accurately polar align the mount by some means anyway, so that scale is only there to get you close to the right latitude.  I don't even use it...I have a cheap laser pointer attached to the mount to get me close to Polaris, then use sharpcap to polar align.  


Edited by sbradley07, 07 March 2021 - 10:33 AM.

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#9 Chris Johnson

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Posted 07 March 2021 - 10:42 AM

gofins72, you are absolutely correct. The angle of the face should be your colatitude which is 90deg minus your latitude. If you put a digital angle gauge on the polar axis shaft, where the counter weight is it should read your latitude. Use the hand control to rotate the mount 90deg, put the scope on it parallel to the polar axis and Polaris should be in the eyepiece view. From an old mariner.


Edited by Chris Johnson, 07 March 2021 - 10:56 AM.

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#10 SteveInNZ

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Posted 07 March 2021 - 03:14 PM

Have a look at a (picture of a) Star Adventurer, which is what the wedge is designed for. The RA axis is 90 degrees to that of the Az-GTi, relative to the wedge mounting face.

When the wedge is set for 0 degrees on the scale, the scope on the SA would be horizontal (as you would expect on the equator). With your setup, the scope would be vertical.

As you've already worked out, you need to subtract your latitude from 90 degrees. Now you also know why.

 

Steve.


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