Balancing the scope for astrophotography

[dugnsuz (Doug)]

Hi,
After spending about a year taking pics with my pentax DSLR and a few different camera lenses on a RA driven EQ4 mount with no tracking problems, I took the plunge and bought an ED80. Out tonight to take a few pics of moon - very nice.
Turned to Eta C for a rough deep sky test - first pic 90sec exp had really bad star trails. Motors were running OK, counterbalance is approx 4.5kg.
Suddenly realised I didn't know the best way to balance the scope for photography!!!
Is there a method? If the weight is low on the shaft the scope overbalances to one side, too high the same. Can't seem to find a sweet spot.
Is the counterweight too heavy for the setup?
Any tips
Thanks in advance
Cheers
Doug

[ballaratdragons (Ken)]

Doug, it has been my understanding that you balance the scope perfectly, then move the counterweight about a Fairies fart along the shaft towards the end. That way the drive gears are always neatly meshed but there is no excessive weight on the drive. But only move the counterweight a fraction, like about 1mm. Barely noticable!

I got this tip of several sites, and it works for me anyway.

[dugnsuz (Doug)]

Originally Posted by ballaratdragons

Doug, it has been my understanding that you balance the scope perfectly, then move the counterweight about a Fairies fart along the shaft towards the end. That way the drive gears are always neatly meshed but there is no excessive weight on the drive. But only move the counterweight a fraction, like about 1mm. Barely noticable!

I got this tip of several sites, and it works for me anyway.

Thanks Ken,
I'd convinced myself focusing would be my major problem, forgetting totally about balance issues!!
I'll google to get some more tips, but it looks like I'm putting excessive weight on the drive!?
Attached my very first ED80 pic too
Cheers
Doug

[Dennis]

Hi Doug

As Ken says, I have also heard of this slight imbalance technique:

• OTA on W of mount - slide CW down shaft to produce a slight imbalance, making the DEC shaft/CW slightly heavy on the E.
• OTA on E of mount - slide CW up the shaft to produce a slight imbalance, making the OTA slightly heavy on the E.

That way, the RA gear(s) are always meshed due to the slight imbalance.

Cheers

Dennis

[dugnsuz (Doug)]

Originally Posted by Dennis

Hi Doug

As Ken says, I have also heard of this slight imbalance technique:

• OTA on W of mount - slide CW down shaft to produce a slight imbalance, making the DEC shaft/CW slightly heavy on the E.
• OTA on E of mount - slide CW up the shaft to produce a slight imbalance, making the OTA slightly heavy on the E.

That way, the RA gear(s) are always meshed due to the slight imbalance.

Cheers

Dennis

Thanks Dennis,
So in an imaging session, would you balance the scope depending on which side of the mount the OTA is being used on?

Doug

[Phil]

Hi Doug one thing i have found is that if there is a problem with guiding 99% of the time it is balance. As Dennis has said above is a good start. Also balance the scopes in the DEC to.
Phil

[Dennis]

Originally Posted by dugnsuz

Thanks Dennis,
So in an imaging session, would you balance the scope depending on which side of the mount the OTA is being used on?

Doug

Yes - when a German Equatorial Mount crosses the Meridian, you need to shift the CW on the Dec shaft accordingly, to ensure that the E side of the mount is slightly heavy. This should ensure that the RA gear(s) are always meshed, as the slight imbalance should encourage the gears to always be pressed against each other, rather than have any small gaps (backlash) before the mesh is taken up.

My non-engineers interpretation!

Cheers

Dennis

[[1ponders] (Paul)]

Also consider your dec balance. Get all your gear loaded, place your shaft and OTA in horizontal position and check to see if you are nose or rear heavy in your scope. Slide forwards or backwards to adjust as needed. (bring it back to the verticle first, it's easier that way ) Keep sliding and adjusting until perfect.

Now if you want to get really pedantic, find a star, center it, and watch which way it drifts in DEC. If it drifts north and you are pointing either north then make the nose just a wee bit heavier, if pointing south make the tail a bit heavier.

Similar reason to the RA. If you have backlash then this should help prevent some of the backlash from affecting your guiding adjustments.

[JohnG (John)]

Here is a link to show you with photos, how to balance a telescope on a GEM:

http://www.aozc64.dsl.pipex.com/tips....htm#balancing

Shows both 2 way and 3 way balancing.

Cheers

JohnG

[[1ponders] (Paul)]

Thanks for that link John, some great losmandy fixes there

[ballaratdragons (Ken)]

Originally Posted by JohnG

Here is a link to show you with photos, how to balance a telescope on a GEM:

http://www.aozc64.dsl.pipex.com/tips....htm#balancing

Shows both 2 way and 3 way balancing.

Cheers

JohnG

Obviously the member from the Wilmslow Astro Club who wrote that article mustn't have any Backlash, or has never heard of slight off-balance for Astrophotography.

I used to do perfect balancing, but backlash always reared it's head. Not any more.

[JohnG (John)]

True Ken, true.

I never use perfect balance for astrophotography, my mount is weighted slightly to the east all the time, there again I have very little backlash.

Cheers

JohnG

[dugnsuz (Doug)]

Thanks for all the info chaps!

[Shawn]

Push the weight, and dont guide the fall,



Works for me...