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Tandem and CG5 GOTO question

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#1 vdb

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Posted 27 February 2010 - 02:08 PM

I would like to mount 2 items on my CG5 goto,
a dslr with lens and a light short tube refractor to do guiding.
However if you mount them in tandem, they point the other way as when you mount one scope, the equipment is 90 degrees rotate. Question is, how will alignment and goto work?

Thanks,
Yves.

#2 mclewis1

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Posted 27 February 2010 - 02:30 PM

The mount doesn't know anything about those index position markers, you can actually start it off in any orientation you like, as long as you're consistent about the starting point.

To make life a little easier though you have two options. Turn the saddle 90 degrees, mount the side by side plate and then either move (un peel and re position) the index marks 90 degrees to match the new orientation or if you're using hand controller firmware level gem4.15 or higher leave the marks alone and use the new OTA Orientation routine to tell the mount about the different orientation offset (90° E or W, or 180°). The information about this new routine is in either the CGEM or CGEPro manuals.

#3 vinnie

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Posted 27 February 2010 - 02:36 PM

Makes no difference. star alignment is relative to the start or "Parked" position. With a side by side arrangement you are starting from Dec 0° instead of Dec 90° but the software will interpret that as a start at Dec 90°.

#4 David Pavlich

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Posted 27 February 2010 - 03:05 PM

I have a question about the SBS on the CG5. Frist, is the CG5 that you have powered by the newest firmware or the older firmware? The second question for those that own the CG5, does it use a switch position to find home like the CGE? If so.....

and it has the old firmware, it might not be able to do a full star align just as the older CGE couldn't do it with the Dec axis turned 90°. Well, you can do the first 2 stars on the west side of the meridian, but when you go to the east side, the mount thinks that there is a cone error of 90°, not that you have turned the mount 90° to compensate for the SBS install. The first alignment star you choose in the east will be off by, you guessed it, 90°. Just thought that I'd mention it.

David

#5 vdb

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Posted 27 February 2010 - 03:39 PM

It is the gem 4.16 firmware
I don't know about a switch to find the home position, I put it manually on the index markers before I start to align.
Rotating the saddle is not possible I think, as the plastic that contains the motor is not symmetric.
I'll check if I have the option in the menus to tell the mount a different offset orientation.

#6 vdb

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Posted 27 February 2010 - 03:43 PM

Ah just checked the menu,
In Scope Setup, i have:
OTA orientation, this can be;
Normal
East
West
So if my lens would be pointing to the east I would select east I guess.

#7 mclewis1

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Posted 27 February 2010 - 04:11 PM

The second question for those that own the CG5, does it use a switch position to find home like the CGE? If so.....David

David, No switches, it's the same as the CGEM, just stickers so it can start anywhere.

#8 mclewis1

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Posted 27 February 2010 - 04:16 PM

Rotating the saddle is not possible I think, as the plastic that contains the motor is not symmetric.

Yves, I meant that you just turn the saddle sideways so the SbS mounted scopes point in the same direction as a single scope. You are correct in that you cannot turn the saddle with respect to the shaft.

#9 vdb

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Posted 27 February 2010 - 04:49 PM

Yves, I meant that you just turn the saddle sideways so the SbS mounted scopes point in the same direction as a single scope. You are correct in that you cannot turn the saddle with respect to the shaft.


Ah Ok,
so best I would do is let them point sideways, and change the ota orientation in the menu.
I think that if I point them as a single scope, somehow things will go wrong ... no?

Tx,
Yves.

#10 mclewis1

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Posted 27 February 2010 - 05:27 PM

Yves,
Yes, point them sideways, keep the index marks in their original positions and then set the OTA orientation East or West depending on which way the scopes are pointed. You only have to set the OTA Orientation once and it shouldn't ever change unless you put the scopes in the tandem or SbS mounting upside down (yes it's very easy to do) or reset the hand controller.

This way you can continue to use the original index marks to start off from. The mount will understand that the scopes are pointed off to one side and will take that into account when you ask it to do a 2 star alignment. The mount should then put that first alignment star in the field of the finder scope, just like it did before. Your gotos will be just as accurate as before ... but only for the scope that you're doing the alignment through. The other scope beside it will usually be off a little bit. You can fix this by adjusting the bolts that hold the saddles to the tandem bar or by adding shims between the saddle and the tandem bar.

#11 vdb

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Posted 28 February 2010 - 04:23 AM

Thanks Mark,
now of to find a good way to attach a nikon d300 with old 300mm 2.8 ... to the tandem plate ... not so easy.
The other scope will be a cheap 80mm to do guiding with Baader LVI, so they don't need to point exactly to the same point, neighborhood should be enough.
Yves.

#12 mclewis1

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Posted 28 February 2010 - 09:40 AM

Yves,

Losmandy and ADM make nice 1/4" camera attachments that ride on a variety of dovetails. Something like this or the Losmandy VCM if you need to mount closer to the bar.

The size and weight of your 300mm and any "play" where it attaches to your DSLR may cause a bit of sag that might show up on the edges of your shots. If you see this problem you could also use a single 3 point ring on a V saddle to add support to your 300mm lens. You'll probably have to craft some spacers to get the height of the ring to accurately match the center line of the camera but that shouldn't be too difficult.

#13 vdb

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Posted 01 March 2010 - 11:46 AM

Mark,
I ordered already a bar so I can mount the 2 items,
and also the vixen camera tailbar. I will fix this tailbar to the lens (and try to secure it so the lens cannot loose itself under its own weight)
Your proposition is better, however the issue is that the puzzle becomes complex rather quickly and I cannot check this in a store, I need to order everything online ... Making mistakes can become expensive.

Yves.






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