Reducing flexure

[Carl]

Hi folks
will i reduce the chance of flexure by mounting my C8, 80ed and 9x50 guide scope on a side by side plate?
Currently i have my 80ed piggy backed on he C8 and now need to find a location for my 9x50 guidescope preferable central to both imaging scopes.

This will be mounted on a NEQ6 pro mount

Cheers Carl

[Moon]

Probably not. If the flex is coming from either focuser or the primary mirror moving then it won't improve the situation.
Personally I find side by side harder to balance too.
James

[The_Cat]

Difficult question to answer. Minimizing differential flexure is a matter of sound mechanical construction. Piggy backing can lead to higher overall loads on the mount as one needs to increase the counter weights quite a bit to balance the added load away from the RA axis.

Here is an example of a plate for side by side mounting notice the added bars (machined) on underneath that are fixed with many screws.



http://lh5.ggpht.com/_nmcM5hLJalE/TMAXrJfUKHI/AAAAAAAAAKg/GTrx52aUXSY/s800/Plate_1373.jpg

For those interested. The above plate is machined out of Aluminium Alloy 6081 that has a small proportion of Titanium.

[Alchemy]

The biggest issue is rigidity, if the plate is rock solid then yes..... But most side by side setups are a bar with dovetail sliders in which to put separate bars with more screws..... Not the best choice.
I use a large plate about 16 inches square annealed aluminum ( much harder than regular aluminum) and bolt the rings to that. No noticeable flexure at 1000 mm

[Carl]

I was thinking about it today after looking at a friends set up where he has a side by side plate. To do this it will set me back around $500 just to have all of my scopes on the mount at once. Alternately i can continue with the dovetail setup that i have now.

I was thinking that maybe if i am going to shoot thru the ED80 i may as well just have that on the EQ6 mount for the month. Then change when i want to shoot thru the C8. What do you think?

I can mount a 9x50 guidescope very, very securely on top of the ATO. Do you think there will be any noticable flexure? my friend has none.

Also if i change over scopes i obviously will have to re balance the set up.
Will this effect the accuracy of my guiding?

Love to hear your opinions

[mldee]

I finally took that approach and am very happy with it. Changing scopes is not a big deal, and rebalancing basically only requires a simple slide of the weights. Changeover takes about 5 minutes at worst. YMMV.

[Barrykgerdes]

Differential flexure is always going to be a problem no matter how rigidly you mount your two scopes together. The flexure between the two OTA's is fixed by making them "as one'' with suitable "bonding". However the flexure caused by small movements in individual mirrors, focusers etc is much harder to control.

The only satisfactory method is to guide from the same optical path as your camera. This can be achieved with an off axis guider. However this limits the selection of suitable guide stars.

At the ASNSW photo group meeting this month we were shown a way of using a combined method of using one guider to control the other to correct errors. This allows extremely long exposures without any errors caused by flexure. Software to help this is available. If you live in Sydney I can recommend this group. Meetings times and dates are on the ASNSW web site.

Barry

[gregbradley]

Hi Barry,

What was the method and can you provide a link to the software?

greg.

[Barrykgerdes]

Sorry I don't remember the details. You will need to come along to a meeting and talk to Mike.

Barry

[multiweb]

The only effective way would be to use an OAG.

[davewaldo]

If you do wish to mount all scopes at once you may consider mounting the guidscope under the C8 like shown towards the bottom of this thread: http://www.iceinspace.com.au/forum/showthread.php?t=64805

This won't solve flexure issues but it shouldn't add to them.

You don't actually say if you have flexure issues at the moment. If you don't have any issues then I'd be saving the $500.

Let us know how you get on :)