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Celestron VX Mount Tracking Test

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#1 Jeff2011

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Posted 07 April 2013 - 10:12 AM

I have only had my VX mount for just over a week now and am still learning how to use it. During the second night out with it, I decided to test how well it tracked unguided. Here were my procedures for aligning before my test.

1. Polar align on Polaris with reticle eyepiece
2. 2 star alignment + 3 calibration stars
3. Polar alignment via hand controller polar align function
4. 2 star realignment + 3 calibration stars

I then barlowed my reticle eyepiece (12.5mm ep + 2x barlow) and tracked a star for 15 minutes. Did this on two stars on either side of the meridian. The double crosshair lines of the EP make a small box at the center and after 15 minutes the star moved from the center of that box to the edge of the box. This was a very smal movement.

I then decided to break out the DSLR to see how long an exposure I could take before getting star trails. The DSLR was mounted to my Astro Tech 72ED with a focal length of 430mm. I was able to get a 2 minute shot with round stars. However 3 minutes resulted in some star trails.

I was very pleased with these results.

Is this pretty much the upper limit of what I can expect without guiding, or should I be able to do better?

Is the polar alignment function of the hand controller going to give me as good a results as a star drift alignment?


Jeff

#2 Raginar

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Posted 07 April 2013 - 10:37 AM

Jeff,

Nothing will beat a drift alignment. The software gets you close but it's based on an imperfect model. A drift alignment is based on observation.

#3 budman1961

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Posted 07 April 2013 - 11:00 AM

I generally do the 2 star align, then add 4 calibration stars, then the polar align routine. I dont redo the alignment and calibration stars however.

With a DSLR attached, I can get round stars up to 110 seconds..I have heard with a guider, 5 mins isnt out of the question.

Andy

#4 Whichwayisnorth

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Posted 07 April 2013 - 01:04 PM

Here is an 90 second unproccessed exposure taken through my 8" EdgeHD on the AVX mount. No guiding. Just 2+4+ASPA anything over 90 and I was getting tic-tack shaped stars. I was reduced using the Optec Lepus .62x reducer. Shot with my modified canon t1i.

Edit: found a 90 second test at 800iso. That is why it is so dim.

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#5 Whichwayisnorth

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Posted 07 April 2013 - 01:04 PM

Here is a zoom in on one star towards the inside of the photo.

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#6 Whichwayisnorth

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Posted 07 April 2013 - 01:11 PM

here is one towards the outside of the photo.

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#7 Jeff2011

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Posted 07 April 2013 - 02:02 PM

Jeff,

Nothing will beat a drift alignment. The software gets you close but it's based on an imperfect model. A drift alignment is based on observation.


That is what I was thinking too. Just wanted to get another opinion. I am no stranger to star drift alignments since I have done it on my EQ platform many times. Since my light polluted skies limit my exposure time the mount polar alignment appears to be acceptable for the focal length I am using. Might try a star drift next time just to experience it with the mount. Thanks

#8 Jeff2011

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Posted 07 April 2013 - 02:05 PM

I generally do the 2 star align, then add 4 calibration stars, then the polar align routine. I dont redo the alignment and calibration stars however.

With a DSLR attached, I can get round stars up to 110 seconds..I have heard with a guider, 5 mins isnt out of the question.

Andy


Andy, the manual recommends realigning and calibrating after a hand controller polar alignment.

#9 Jeff2011

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Posted 07 April 2013 - 02:09 PM

Here is an 90 second unproccessed exposure taken through my 8" EdgeHD on the AVX mount. No guiding. Just 2+4+ASPA anything over 90 and I was getting tic-tack shaped stars. I was reduced using the Optec Lepus .62x reducer. Shot with my modified canon t1i.

Edit: found a 90 second test at 800iso. That is why it is so dim.


Thanks for posting your results. Your focal length is much longer than mine even with the reducer. That probably explains why I am getting 120 seconds with no trailing to your 90.

#10 Whichwayisnorth

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Posted 07 April 2013 - 02:20 PM

Here is an 90 second unproccessed exposure taken through my 8" EdgeHD on the AVX mount. No guiding. Just 2+4+ASPA anything over 90 and I was getting tic-tack shaped stars. I was reduced using the Optec Lepus .62x reducer. Shot with my modified canon t1i.

Edit: found a 90 second test at 800iso. That is why it is so dim.


Thanks for posting your results. Your focal length is much longer than mine even with the reducer. That probably explains why I am getting 120 seconds with no trailing to your 90.


Correct. When I was using my reduced to f/4 80mm refractor I could go well over 3 minutes unguided. In fact at one point I had it so dialed in I got 17 minutes of drift aligning and the star never moved from center.

#11 budman1961

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Posted 07 April 2013 - 03:45 PM

Jeff and Michael,

After you finish the polar alignment, to you power off the mount and then do the 2 star and 4 calibration stars? Ive seen somewhere that people do this also. What fo you all do?

Andy

#12 Jeff2011

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Posted 07 April 2013 - 03:56 PM

After the polar align, I do not power off the mount. I slew to a star, press align and replace one of the previous aligned or calibrated stars.

#13 Whichwayisnorth

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Posted 07 April 2013 - 04:11 PM

No I don't. I just move on with the night. Go-to's are spot on and there is no drift. I wasn't aware I was being encouraged to do any further syncing or replacing alignment stars. I guess it couldn't hurt. Perhaps next time.

FYI, I typically connect using The Sky X. I have t-point so I spend about 20 minutes doing some sky modeling to get my go-tos perfect. When I am done for the night I hibernate the scope and save my t-point model.

#14 DaveJ

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Posted 07 April 2013 - 05:40 PM

I generally do the 2 star align, then add 4 calibration stars, then the polar align routine. I dont redo the alignment and calibration stars however.

With a DSLR attached, I can get round stars up to 110 seconds..I have heard with a guider, 5 mins isnt out of the question.

Andy


Andy, the manual recommends realigning and calibrating after a hand controller polar alignment.


Not for the later releases of the firmware. With these, realignment isn't necessary.

#15 Kendahl

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Posted 07 April 2013 - 08:19 PM

Were you using periodic error correction? If not, that should help significantly.

#16 Jeff2011

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Posted 08 April 2013 - 08:29 AM

Not for the later releases of the firmware. With these, realignment isn't necessary.


Thanks Dave. I will check my firmware version and see if it is out of date.

#17 Jeff2011

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Posted 08 April 2013 - 08:36 AM

Were you using periodic error correction? If not, that should help significantly.


Nope. Don't have an autoguider yet. According to the manual (sorry that is all I have to go by right now), PEC requires an autoguider to get it configured. Please correct me if I am wrong. This is my first GEM.

I have been eyeballing the QHY5L II Mono. Others have suggested that over the Orion Autoguider.

Right now I am trying to see what I can get with unguided shots. Unfortunately the clouds have prevented me from doing that. It cleared off last night so I tried to set up. Was able to site in on Polaris and by the time I got to my second alignment star, the clouds rolled back in. Bummer. :(

#18 zawijava

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Posted 08 April 2013 - 08:39 AM

Could someone post a link to the AVX Firmware updates. I checked out the Celestron Support but didn't see anything [specifically] for the AVX :question: thanks, Tim


Not for the later releases of the firmware. With these, realignment isn't necessary.


Thanks Dave. I will check my firmware version and see if it is out of date.



#19 Jeff2011

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Posted 08 April 2013 - 08:57 AM

Tim,

I didn't see anything either. Is the manual then out of date regarding realinging after a hand controler polar alignment?

#20 DaveJ

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Posted 08 April 2013 - 09:04 AM

Tim,

I didn't see anything either. Is the manual then out of date regarding realinging after a hand controler polar alignment?


I'm going to venture a guess that you are correct. Somebody just did a copy/paste of that section of the manual from the CG5. The CGEM/CGEM DX/CGE/CGE Pro firmware updates eliminated the requirement of shutting off the mount and realigning after the ASPA routine was done. I've always kept my Celestron mounts at the current firmware levels. My plan is to pick up an AVX at NEAF weekend after next. Celestron has not been good, at all, about keeping the manuals up-to-date after firmware revisions. That's been the case for years now.

#21 Jeff2011

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Posted 08 April 2013 - 10:21 AM

Thanks Dave.

That is why I look at manuals with a grain of salt. I am in the software development business myself so I know how it goes with documentation. I am just glad to be able to tap into the knowledge and experience of CN members like yourself.

#22 cn register 5

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Posted 08 April 2013 - 01:23 PM

I've just looked at the AVX manual. Page 30.

It doesn't say anything about cycling the power. It says that it is a good idea to check the alignment and talks about replacing alignment and calibration stars but doesn't say that you have to.

Anyway you don't have to cycle the power or do a relignment. Checking a goto is a good idea but you should do it before doing the polar alignment as well as afterwards.

My opinion is not to bother with a polar finder but get a reticle EP. I use a simple home made one

And treat CN with a pinch of salt, not everyone distinguishes opinion or speculation from fact. I've seen a lot of statements made with total confidence that I know to be wrong.

Chris

#23 DaveJ

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Posted 08 April 2013 - 02:56 PM

And treat CN with a pinch of salt, not everyone distinguishes opinion or speculation from fact. I've seen a lot of statements made with total confidence that I know to be wrong.


Man, you have THAT right! Take a look at some advice here that a member gave: link. :foreheadslap:

#24 Jeff2011

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Posted 08 April 2013 - 03:13 PM

After the polar align, I do not power off the mount. I slew to a star, press align and replace one of the previous aligned or calibrated stars.



Chris,

The above is from one of my previous replies in this post. I do not power the mount off, but I did follow their recommendations on replacing the alignment and calibration stars after a hand controler polar alignment.

I read through Dave's response too fast and missed the power off part. I am assuming that the power off recommendation came from the CG5 manual. So then Celestron must have updated the AVX document.

Anyways. Hope I did not start a war here :grin:.

#25 cn register 5

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Posted 08 April 2013 - 04:53 PM

This realign myth seems to come from previous polar align methods and methods for other mounts where the alignment is not preserved. I don't know about the original CG5 because I never tried it but it could well be true for that one.

That was 5 years ago or more and the software has moved on - at least the Celestron software has.

Once you have an alignment matrix it is quite easy to apply the altitude and azimuth rotations to that matrix to transpose it to a new coordinate system.

Of course if you have done a poor alignment in the first place then the intial gots and correction error will be poor. After a "polar alignment" not only will your polar alignment be bad but your gotos will still be bad. Garbage in garbage out.

And the mount gets blamed.

In my opinion if you don't use a reticle EP you can forget about precision, in gotos or polar alignment.

Chris






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