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Dovetail Position

beginner equipment mount reflector
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#1 Calla1995

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Posted 27 May 2019 - 08:02 AM

Hi all,

 

I have been pondering for a while what the benefits are of the positioning of the dovetail is? Is there a set fore/aft position it should be or just slap bang in the middle? I have a reflector telescope that is mounted on an EQ-3 mount.

 

Many thanks!



#2 kathyastro

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Posted 27 May 2019 - 08:24 AM

The dovetail allows you to adjust the position in order to achieve a good balance.  It is important to balance the scope in all directions so that its weight is not pulling it off your target.  On a motorized mount, balancing reduces the load on the motors.  On a manual mount, balancing makes it easier to move the scope to the desired location and not have to fight against its weight.

 

Rotate the mount so that the scope is horizontal.  Then release the declination clutch.  The scope should not move in either direction.  If it wants to fall in one direction or the other, you need to move the dovetail until it balances.


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#3 Calla1995

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Posted 27 May 2019 - 08:31 AM

The dovetail allows you to adjust the position in order to achieve a good balance.  It is important to balance the scope in all directions so that its weight is not pulling it off your target.  On a motorized mount, balancing reduces the load on the motors.  On a manual mount, balancing makes it easier to move the scope to the desired location and not have to fight against its weight.

 

Rotate the mount so that the scope is horizontal.  Then release the declination clutch.  The scope should not move in either direction.  If it wants to fall in one direction or the other, you need to move the dovetail until it balances.

Hi Kathy,

 

Thanks for your response. I normally balance the telescope by loosening the tube rings and shifting the telescope slightly either direction until it is balanced for that part of the process. I never normally touch the position of the dovetail. So should I be adjusting the fore/aft position of the dovetail or keep adjusting the tube rings to balance the scope?



#4 kathyastro

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Posted 27 May 2019 - 08:52 AM

Hi Kathy,

 

Thanks for your response. I normally balance the telescope by loosening the tube rings and shifting the telescope slightly either direction until it is balanced for that part of the process. I never normally touch the position of the dovetail. So should I be adjusting the fore/aft position of the dovetail or keep adjusting the tube rings to balance the scope?

You can do either one.  Most people find it easier to use the dovetail.

 

If you are concerned about lateral balance, you will need to rotate the OTA in the rings to establish a lateral balance position.  At that point, you would not want to fiddle with the rings or you would risk messing up the lateral balance.  If you don't care about lateral balance (i.e. you are not doing AP), then it is not a big concern.



#5 wrvond

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Posted 27 May 2019 - 09:19 AM

Another consideration to keep in mind when balancing your scope is contact with any part of the mount or tripod. After you have balanced the scope to your satisfaction you should move it through it's entire range of motion to ensure it won't go bump in the night.


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#6 Dynan

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Posted 27 May 2019 - 10:06 AM

The dovetail allows you to adjust the position in order to achieve a good balance.  It is important to balance the scope in all directions so that its weight is not pulling it off your target.  On a motorized mount, balancing reduces the load on the motors.  On a manual mount, balancing makes it easier to move the scope to the desired location and not have to fight against its weight.

 

Rotate the mount so that the scope is horizontal.  Then release the declination clutch.  The scope should not move in either direction.  If it wants to fall in one direction or the other, you need to move the dovetail until it balances.

Kathy, other times you mention Back Heavy (camera end) or Front Heavy (objective end). Also there is the 'East Heavy' admonition.

 

Could you clarify your thoughts on Balanced or Heavy (any direction)?



#7 kathyastro

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Posted 27 May 2019 - 10:38 AM

Kathy, other times you mention Back Heavy (camera end) or Front Heavy (objective end). Also there is the 'East Heavy' admonition.

 

Could you clarify your thoughts on Balanced or Heavy (any direction)?

For visual use, since we are on the Beginners' Forum (no AP), there is no compelling reason to deliberately unbalance the mount.  Deliberately unbalancing (by a very small amount!!) is used to load the gears of a motorized mount to eliminate backlash.  If you find that backlash is a problem with visual use, then by all means give it a try, but it is mostly applicable to AP.

 

To remove backlash in declination, you can set either the front end or the back end heavy.  It doesn't matter which you do.  To remove backlash in RA, you want the east side heavy, whether that is the scope or the counterweights.  That ensures that the motor is always lifting, never lowering, and keeps the gears smoothly loaded.


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