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Celestron VX mount

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#626 nine44

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Posted 30 April 2013 - 10:03 PM

Regarding re-alignment of the AVX after a successful polar align... It seems there may be an easier way, but I'm not seeing it.

I generally do a 2+4 alignment and then polar align. If there is significant correction during the polar align process, it can effect pointing accuracy, so it is best to recalibrate the mount. After polar alignment, it would be easier to just send the mount back to the home position and do a new alignemnt.

Right now, I have to unsync my polar align star. Then back out of the alignment menu. Slew to one of the original alignment stars. Then go back to the align menu and select alignemnt stars and then "replace." Then back out and slew to the second star--then back to alignment stars and "replace." Hopefully you get the picture.

Anyone know of a way to send the mount back to its home position after a polar alignment? Or am I missing something BIG?

#627 FacEngRet

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Posted 30 April 2013 - 10:31 PM

You can go back to the home position by pressing MENU/Utilities/Home Position/GOTO and then pressing enter. I made a small laminated copy of the menu tree found on page 23 and 24 of the manual and keep it in my shirt pocket. I used it a lot at first, but now, a couple months later, a rarely look at it. I usually do what you want to do. I un-sync from the polar align star, goto home and do a new 2+4. Doesn't take long and I have had good success doing so.

#628 dr.who

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Posted 01 May 2013 - 01:14 AM

Actually you would push "Back" until you see the "Celestron AVX" displayed then follow FacEngRet's directions.

#629 cn register 5

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Posted 01 May 2013 - 02:44 AM

The simplest procedure to get a good alignment after an ASPA is to do nothing. At most do an unsync or a new sync.

The scope knows the polar alignment error and when ASPA is done rotates the alignment matrix by the polar alignment error.

It is easy to test this, do a few slews to bright stars, centre them and use the Identify procedure. This will give you the distance the mount thinks you are from the star.

Chris

#630 nine44

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Posted 01 May 2013 - 07:22 AM

The simplest procedure to get a good alignment after an ASPA is to do nothing. At most do an unsync or a new sync.

The scope knows the polar alignment error and when ASPA is done rotates the alignment matrix by the polar alignment error.

It is easy to test this, do a few slews to bright stars, centre them and use the Identify procedure. This will give you the distance the mount thinks you are from the star.

Chris


Chris--my experience is--after doing a 2+4 alignment and making a significant polar alignment adjustment, the slews are off. My AVX doesn't seem to be adding the erro rlike you mention. Also, the user manual suggests re-aligning after a polar adjustment. INterested to know if I am missing something.

#631 cn register 5

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Posted 01 May 2013 - 08:04 AM

Nobody needs to take my word for this.

You can all measure the change in alignment accuracy that an ASPA causes:
  • Do an alignment as normal.
  • Slew to a few stars and use the Identify function to get an idea of the pre ASPA alignment accuracy.
  • Do the ASPA.
  • Slew to a few stars and use the Identify function to get an idea of the post ASPA alignment accuracy.
This process is called Science. People have been doing this sort of thing to find things out for about 500 years now.

Chris

#632 nine44

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Posted 01 May 2013 - 08:12 AM

Chris--wasn't trying to insult you. I'm just trying to understand how it works. There are alot of scientists on this forum--and all of us are pursuing knowledge--sometimes asking stupid questions to get to a deeper understanding. All I know (which is not much) is that after the polar alignment, my GOTOs are off and the manual seems to echo what I'm experiencing. I guess I'm wondering if my mount is accounting for the calculated error you mention yours is.

#633 bunyon

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Posted 01 May 2013 - 08:31 AM

It may well have to do with how large an initial polar alignment error you have. I've been polar aligning EQs for over 30 years and, frankly, my initial alignments are pretty good.

Not sure what the average is, but when I do ASPA with the VX, it is rare to not have the target star in the eyepiece. So adjustments are minimal. Given that experience, I find that once I unsync the target star, my gotos are fine.

It may be that if your initial alignment is too far off, the computer can't correct. An easy experiment, and I'll try it next time I'm just playing around, would be to intentionally set up with the mount far from aligned.

In any case, I strongly recommend you try to get as close to aligned as possible at initial setup. If you are doing this and you're pretty close and the gotos are off after ASPS, I'd be interested to here.

#634 dcbrown73

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Posted 01 May 2013 - 08:42 AM

My Celestron VX mount just arrived yesterday. It's my first EQ mount so I've got some learning to do. I purchased it for a new ES 80mm APO refractor I bought at NEAF, but fully plan on throwing my 8SE OTA on it also from time to time.

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#635 Stew57

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Posted 01 May 2013 - 10:43 AM

I have done
2+4 alignment
Slew to objects and see where on my camera chip they fall
Do ASPA
Slew to same objects and see where on the camera chip they fall.

Depending on how far off my original polar alignment was I may have to redo an alignment to get my original accuracy back. Derik at teamcelestron will substantiate that.

I have not asked but I notice that the calibration stars are removed after ASPA and maybe that is where the accuracy discrepancy occurs.

Anyway my science data does not seem to be the same as your science data but does seem to correlate well with Nine44's. Those kind of discrepancies in data have been going on for as long as scientific enquiry has been practiced. The key to science is finding out why they are there.

#636 Carl N

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Posted 01 May 2013 - 11:20 AM

I may not use the easiest method, but I do the 2+4, then ASPA. Then I go to home position, turn off my mount, turn it back on, and do the 2+4 again. By rebooting, I don't have to unsync and replace alignment stars.

I have found, using a 5mm illuminated cross hair eyepiece, that if I do the 2+4, ASPA, reboot, 2+4 again, ASPA again, reboot, 2+4 again - that I get really tight results.

By doing that sequence twice I eliminate micro error and when I use identify, I am spot on.

Carl

#637 Jeff2011

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Posted 01 May 2013 - 11:24 AM

It'd be nice if any owner could try some unguided pics with dslr and 200-300mm FL lens for testing tracking accurancy...


Not exactly what you asked for, but here are my results with a 430mm focal length refractor. These results also show the accuracy of an ASPA with DSLR star drift results after the ASPA. This is unguided, no PEC.

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#638 bunyon

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Posted 01 May 2013 - 12:07 PM

I put this up in another thread but, perhaps, not many saw it.

I roughly aligned by sight, did 2+4, did ASPA. Gotos were within the field of view after unsyncing from target star in ASPA. I then did guided and unguided imaging. I then did a PEC recording and again did guided and unguided. I also tested how far I could go with a guided image.

EDIT: the RA drift is scanning east for 30s and then west for 25s. I found no adjustments necessary after ASPA.

The results are in the image. I used a C8 with reducer (1200mm EFL) and Orion finder guider. I think certainly with PEC unguided for a couple minutes at 200mm should be fine. Guided you could go as long as you want.

I did ask in the other thread, why the fascination with unguided? It's not hard to guide.

EDIT2: Since we're talking science, the sample size here is much bigger than it looks. 150s unguided pre-PEC had 25% failure rate in 20 tries. I got 20 good ones after PEC. Unfortunately, n=1 for the 900s image. But in 20 300s subs, all were fine with PEC and guiding.

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#639 Jeff2011

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Posted 01 May 2013 - 01:11 PM

I did ask in the other thread, why the fascination with unguided? It's not hard to guide.


My results are from another thread as well. I also received a similar question from another CN member in that thread. I think it has to do with us AP newbies trying to take it one step at a time to become proficient with short duration unguided shots before adding the addtional equipment and learning curve required for autoguiding. So our interest is in how long we can track before needing to go with autoguiding. The problem that I see with unguided AP is that it is not consistent. For example at 1.5 minutes only 44% were keepers. So I do see the wisdom in guiding. I plan on ordering a QHY5L-II guide camera and a guide scope soon, so I am headed in that direction.

#640 nine44

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Posted 01 May 2013 - 01:23 PM

Turn key guiding is a $300 proposition, but it has really help me and likely has maintained my interest / reduced my frustration as I learn. Rather than fight my mount all night long, I just have to get it close and then my SSAG takes over. My light polluted location does prevent me from taking exposures beyond about 1 minute. So winning the accurate tracking / guiding duration contest isn't a goal for me anyway. I really need to get to a dark site.

#641 Alan A.

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Posted 01 May 2013 - 01:29 PM

This VX mount looks promising.

I know very little about computerized GEM mounts so I will ask the following:

for a 4" refractor, how long would the set up be with the VX just to get decent tracking for visual? How long to get decent tracking and GOTO for visual?

It says its rated for 30lb, could the 23lb FS-152 (f/8) be used on this mount for visual?

Thanks,

Alan

#642 bunyon

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Posted 01 May 2013 - 01:38 PM

I usually image unguided with a 50mm lens. The CG5 will go minutes unguided at 50mm. And that is a great way to start AP. However, once the focal lengths get out beyond 200mm, I think it only makes sense to guide - given the cost of everything else you need, a little guider isn't much more.

But, of course, if you can make it work, unguided is simpler and I'm not holding it against anyone for wanting it. I just think long exposure, medium EFL imaging unguided is a lot to ask from relatively inexpensive mounts.


Alan, the AVX doesn't take long to align. For purely visual use, I probably wouldn't bother with ASPA assuming you have a good view of Polaris and can visually align on it. The 2+4 alignment for Goto takes a few minutes - 10 maybe? It can easily be done before full dark.

I have no experience with the refractor, so wouldn't want to guess at whether it wiill hold it well. Seems like a big scope for the mount but I don't know.

#643 gmartin02

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Posted 01 May 2013 - 02:54 PM

My light polluted location does prevent me from taking exposures beyond about 1 minute. So winning the accurate tracking / guiding duration contest isn't a goal for me anyway. I really need to get to a dark site.

Sounds like you could use a light pollution imaging filter - when I started using the Astronomik CLS (clip-in) filter, I was able to double my exposure times. The down side is that I now need to color correct my exposures, but I get a lot better results when imaging emission nebula or galaxies from my "orange zone" site (which is my back yard.)

#644 Carl N

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Posted 01 May 2013 - 03:29 PM

I mount up over 40 pounds and for visual there is no issue. It takes me about 5 minutes to 2+4 for visual and the go to is dead center of my 5mm ilum plossl by the 2+2 point. As stated, for visual, no need for ASPA.

One note, as I get up around 40 lbs, it does become important to ensure rebalancing, especially in RA, as the weight can make the clutch slip if not in balance and I lose alignment.


#645 starbob1

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Posted 01 May 2013 - 03:44 PM

Myself the Tak fs152 is a long scope and heavy. It would benefit from a cgem. The AVX could work but I would not try it. Plus it would look stupid I think. Bob

#646 Alan A.

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Posted 01 May 2013 - 05:03 PM

Plus it would look stupid I think. Bob


Well, the FS 152 would look great on an AP900, but at some point the wallet and wife say - "you're done for a while!" :o

#647 JonM

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Posted 02 May 2013 - 12:38 AM

unless you have a black Atlas.

#648 MartinTreadgold

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Posted 02 May 2013 - 07:23 AM

One think I have noticed, is when you use a polar scope on the mount, the Latitude screw handle is in the way of looking through the polar scope.. anyone else noticed this?

Well, as a half-fix... I swapped the 2 latitude knobs around. it improves the situation somewhat, but not totally great..

If you see dcbrown73's photo above, you can see the knob screw handle i am talking about.. it really gets in the way.

Best Regards

Martin

#649 Carl N

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Posted 02 May 2013 - 09:27 AM

I think that depends on your Latitude. Here in San Diego, at 33degrees, I don't have that problem.

Carl

#650 jonbosley

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Posted 02 May 2013 - 09:39 AM

Anyone using this with a C9.25 and 50mm guidescope? If so what subs are achievable?

Jon






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