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Autoguiding in dec?

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#1 UniversalMaster

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Posted 03 April 2009 - 03:57 PM

Hi!

I'm imaging with a LXD75 which is giving me some trouble. I did a few test tonight, and found that it was better to turn off dec. guiding in PhD. 4min frames looked then ok. But, if I don't guide in dec, should I then

1. Do the normal 2 star alignment (as usual) which will likely result in autostar doing some small ammount of dec-tracking due to imperfect polar alignment

or

2. Use only RA tracking (no alignment), and forget about dec all-thogether?

What do you think?

Do you use dec guiding at all?

Søren

#2 Tim C

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Posted 03 April 2009 - 04:46 PM

I don't think the lxd75 tracks in declination - only in RA. So, if you have dec guiding off you should only be moving the mount in RA. Just make sure you drift align to get a good polar alignment so you can turn dec guiding off (that's what I do).

#3 UniversalMaster

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Posted 04 April 2009 - 12:50 AM

Ok, I thought it would track in dec. since the autostar system is used in both alt/az and Eq setup. It also does satellite tracking, so it IS capable to track in bot RA and Dec.

I don't really like drift alignment... How long do you spend on this? And do you use software like EQAlign to do it?

Søren

#4 Tim C

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Posted 04 April 2009 - 08:13 AM

Hi Soren - I just do it the old fashioned way with a crosshair eyepiece (no drift over 5 minutes at 300x). It takes 30-40 minutes total but usually it's still too light to shoot anyway during most of that time. It becomes second nature with a little practice and you get better at guessing the amount of adjustments with practice. Lot's of folks guide in dec but it can be problematic at times so I figured I'd eliminate one potential source of trouble and just turn it off after doing a very good drift alignment. I know a lot of folks don't like doing drift alignment but call me weird I guess but I sort of enjoy it. I used to have an lxd 75 and when I had the polar scope aligned really well inside the RA axis I frequently was so accurate with using the scope that drift alignment wasn't necessary. I always had trouble keeping that polar scope aligned though so was always afraid to trust it.

#5 jgraham

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Posted 04 April 2009 - 08:51 AM

That's correct, the LXD75 only drives in dec, the dec alignment is only used for GoTo's. I don't drift align, I just use the polar scope, so I usually have a bit of residual drift. With PHD I have it correct the dec in north-only or south-only depending on which one works. How can you tell? Select one or the other, if the guide star drifts in dec then select the other mode. A slight off-balance in dec helps as well if your mount has a bit of backlash.






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