new iEQ45 or used Vixen SX-D ?

orly_andico · Post by **orly_andico** » Thu Feb 10, 2011 4:02 pm

seems iEQ45's also have some DEC guiding problems....

cloud_cover · Post by **cloud_cover** » Thu Feb 10, 2011 5:01 pm

Hmmm.... perhaps mount makers skimp on the Dec axis thinking that photographers will polar align and not get lazy and rely on goto alignment for accurate pointing ;)

Post by **weixing** » Thu Feb 10, 2011 6:16 pm

Hi,

cloud_cover wrote:Hmmm.... perhaps mount makers skimp on the Dec axis thinking that photographers will polar align and not get lazy and rely on goto alignment for accurate pointing ;)

You still need to do accurate polar alignment if you are shooting very long expsoure (that's why you do guiding) and use long focal length scope... even you do guiding. If not, there'll still be star trails appear at the edge of your image cause by field rotation. The main purpose of guiding is to correct periodic error in RA motor.

Have a nice day.

timatworksg · Post by **timatworksg** » Thu Feb 10, 2011 7:29 pm

Sometimes DEC errors also come from a badly balanced scope set up! A piggyback guide scope is always better as it centralizes the payload and less flex overall! Dual mounting dovetails, unless short in length have less chance of flex or balance issues when RA turns, than Dual mount dovetails that spread the 2 scopes far apart! Becomes like a pendulum even though you get the balance right!
The only good thing about IOptron is their handset menu is very easy and clear to use compared to the SynScan. I like the option of being able to select which hemisphere I am in. With the Synscan I have now, I have to trick it by setting SG as S and E (instead of N and E) as my Sirius is pointed South! Also the huge screen makes it a joy to use! And it remembers your settings, time and everything else!! With the Synscan I have to always set time and confirm location every power up! HEnce why I use EQMOD now! Also the addition of the GPS is wonderful!
As Weixing mentioned, hence why theres Autoguiding to correct these errors, as well as PEC software to fix things like this and model the mounts errors so it gets better. But this requires a more permanent set up to model PEC! Using EQMOD, I'm just starting out to model my mounts errors hoping to improve accuracy!
But even with proper drift alignment, good AP still requires some guiding to ensure everything looks good!
Pointing wise for Goto's need good alignment. But everytime you set up, it's back to start again.

cloud_cover · Post by **cloud_cover** » Sat Feb 12, 2011 7:14 pm

Googling more about the SXD's DEC errors threw up this thread:

http://tech.groups.yahoo.com/group/Vixe ... r=1&tidx=1

This guy says that his DEC issue was resolved after tuning his mount such that his DEC backlash could be managed at a value of 20-25. He also recorded PE of +/-5 arcsec.

When using the SXW, the mount was really stiff. It stands to reason that if there's extra friction on the mount, then it is possible for the movement of the motors to be less than completely smooth since the friction would be irregular, leading to jumps in periodic error

Opinions?

orly_andico · Post by **orly_andico** » Sat Feb 12, 2011 9:53 pm

the guy on CN is filling my brain with doubt about the SX-D.

basically he's saying that it's not trouble-free and you need to do tweaking.

Tweaking! then I'd best get a Chinese mount!

I hope Stuart chimes in on this thread, as he has reported DEC issues on his SX-W as well..

Kevin, I think in your case the worms were too tight. The theory is that Vixen overtightens them to compensate for unbalanced loads.