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Terrible RA drifting with a Celestron AVX

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#1 Genryuu111

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Posted 14 June 2017 - 02:20 PM

Hello everyone, I'm new here smile.gif

 

I decided to join, and post, because I have a problem that's been killing me for too long now, and I really cannot manage to solve it myself, using what I can find online.

(If this is not the right place to open this topic, please move it to the right section).

 

I recently bought my first mount and scope, a Celestron AVX 6 newtonian.

 

I live in Osaka, which is extremely light polluted (with your naked eye you can only see planets and stars like Vega and Spica..).

I also have no way to move around right now (but I'm working on it).

 

Anyway, my first goal was to picture planets, and I'm honestly satisfied with wath I managed to do in a few months.

 

saturn 2017-05-18.png

jupiter io ganymede 2017-05-20.jpg

 

(And a short gif I made, a two hours time lapse of Jupiter)

https://media.giphy....rZ60w/giphy.gif

 

 

I then decided I wanted to try some easy DSO.

I know the premise wasn't very good, but without any kind of huge expectation, I bought a light pollution filter, and my first time trying it, using All Star Polar Alignment, I managed to take this:

m27 mini.jpg

It is noisy, comma is terrible, and overall it's a bad picture compared to what people take, but it was my first DSO (and since I've always lived in light polluted places, my first time seeing one in general). The filter did an amazing job, since I would get completely orange skies after 30 second without it.

This picture was a stack of a few exposures I took with various settings, since it was mostly a test. Anyway, I managd to take 2 minutes exposures unguided.

 

And this is where my luck ended.

I NEVER managed to take something decent again, and the more I tried getting better and fixing things, the worse everything got.

 

I learned how to drift align. Even when I get both one east and one south star not to drift in DEC, I have a huge, uneven RE drift. I understand that a mount is supposed to have some sort of periodical error, but this amount is ridiculous. The star moves twice its apparent size within 30 seconds, then stays there for maybe a minute, then maybe move again, maybe wait another minute. It is all quite random.

There are some limits to what I can do from my house, I can only see east to south (kinda). I cannot go close enough to meridian-equator intersection, but even so, using a non ideal star shouldn't affect drift in RE, should it?

 

Anyway, in no temporal order, what I tried to do is:

-Learning how to drift align

-Using ASPA, like many suggest, doing it two or three times in a row (after doing a 2+4 align, and either turning off and on the mount and realign, or overwriting the align keeping the mount on)

-Updating the firmware to the latest version

-Playing around with backslash and RA rate settings

-Trying to balance the mount in different ways. I know it should be "slightly" east heavy, but no amount of perfect balance or east heavy balance makes a difference

-Since nothing worked, I decided to open the mount and play with the gears. RE worm had a huge play. I followed instructions found online, managed to have no play while keeping everything smooth, cleaned and regreased everything. I really thought that was going to fix the problem but no, I still have this RE drift. Before someone comments on me voiding the warranty, from Celestron web page: "The customer shall be responsible for all costs of transportation and insurance, both to and from the factory of Celestron, and shall be required to prepay such costs." This would basically probably cost me as much as a new mount.

 

I will probably buy a guidescope+camera by the end of the month, but I also want advice about that.

Honestly, after I took that first picture, I was really surprised I could do something so nice unguided. And I think stacking enough 2 minutes subs with lowered ISO would have given me decent results.

But now I can't even take 30 seconds subs without having star trails, and at this point I'm afraid I'm either missing something, or the mount has more problems than it should, and with a situation like this, I don't know if a guiding system would fix the problem.

 

This is getting really stressful, I'm basically spending every free hour I have trying to do something about this, and keep failing.

Any kind of advice is welcome, thanks in advance.


Edited by Genryuu111, 14 June 2017 - 10:17 PM.

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#2 einarin

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Posted 14 June 2017 - 02:38 PM

If you can take 30 second unguided exposure with 6" newton,  (which is f/5, ie has 750mm focal length), I'd say is pretty good.

Anyway saying "The star moves twice its apparent size within 30 seconds" is not a very good indicator.

But if you mean like Jupiter then we could say if it's normal - twice Jupiter size is 2x40"=80" which is too much even for that mount.



#3 overnight

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Posted 14 June 2017 - 02:41 PM

Based on your DSO photo, your scope is WAY WAY WAY out of collimation. For a time I had the same 6" Newtonian, I never had that much coma in it.

 

I'm not surprised by RA drifting in the Advanced VX. When it comes to the AVX, some are great, some are terrible. I'm lucky and got a great champ.

Its what you get when you buy a cheap mount (relatively, to me and probably you its tons of $$$).  You'll need to deal with its problems.

 

There is one way to solve your problem. Do a factory reset. No seriously, do it. Its how I solve a majority of the problems I have with it.

 

 

Single 30 second exposure with the C6-N and a SkyView Pro, both of which I sold after 2 weeks to get the 8" I have now.


Edited by overnight, 14 June 2017 - 02:43 PM.

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#4 SkyGibbon

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Posted 14 June 2017 - 02:42 PM

Maybe do a factory reset, enter all your information again, making sure your location and time settings are correct. Do a rough polar align (manually).

On alignment I usually move the scope to the first star choice and then start the alignment while it is in my eyepiece. Starts the alignment quicker, but not sure it has any benefit in the long run.

I always end on an up+right keypress on each star selected. I do a ASPA after intial alignment. I then sync on the PA star afterwards, even though you sync on it prior.

 

Sounds like you have the mechanics down though. The most I ever got unguided with round stars was 60 seconds with an AVX, but that was with an ED-80 refractor. Newts are much more difficult in my eyes. I did get 5min guided (round stars) with a 8" f/5 newt though, on an AVX. Took most the night to get everything right though.

 

As far as a guidescope setup, I use a WO 50mm guider and a Imaging Source 618 mono as my guide camera. Works very well, but you can get close to the same setup......much cheaper. I had the camera left over from an upgrade, and the guidescope can be found for less.

 

Good luck.


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#5 Goofi

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Posted 14 June 2017 - 02:55 PM

First things first, welcome to Cloudy Nights :)

 

As others have shared, some AVXs are good and others not so good. I was lucky and got a good one; but it still had about 40-45 arcseconds of periodic error. The only way I could image DSOs with by guiding ... which fortunately is not that hard to do (but it will cost a little bit of money).

 

My advice is to start with the telescope and get it working as best you can (collimation, coma corrector if you have it), and then tackle the mount.  Make one change at a time and observe the results; take notes on everything - EVERYTHING.  Troubleshooting is a lot easier if we know where you're starting from and what impact each change is having.

 

For my particular AVX, it had problems when imaging at altitudes greater than about 70 degrees ... I could never get it to image well while passing zenith.


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#6 overnight

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Posted 14 June 2017 - 03:03 PM

As you can see, everybody's experience is different. No AVX is the same.



#7 Gipht

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Posted 14 June 2017 - 03:35 PM

I hope you get your scope and mount back on track.  If you bought the C6N reflector with the AVX then we have the same package.  I had similar terrible tracking problems crop up as well and thought there was something wrong with my mount.  I asked for help from the CN community and thanks to them got everything working better then ever.  There is hope.  Let me have you check a few things that were problems for me.

 

1)  The mount movement clutch knob screws in both direction can come loose.  Try tightening them.  When you do your setup hand tighten the clutch knobs fairly tightly.

 

2)  Be sure you are on solid ground where the mount cannot shift.  A level pad of concrete would be best.  I use 12" patio pavers under each tripod leg and those are leveled on pea gravel.

 

3)  Be sure the tripod legs are tightly locked into position, mine had worked loose.  Check the knob under the accessory tray for tightness.

 

4)  There is debate on how level the top surface of the tripod needs to be.  I try to get it very level by using a long carpenter level between the the tightening brackets on the tripod legs.

 

5)  Keep your tripod as short as possible for better stability.

 

6)  I was using drift alignment too and was not aware there was a computerized polar alignment procedure available in the AVX menu.  It is so much easier then drift alignment and it worked great for me.  First do  a two star alignment and then, if possible, add 4 calibration stars. After the 4 calibration stars are complete, slew to a bright star not near the pole, the zenith, or the horizon.  Spica near Jupiter is a good choice.  Press the align button.  Scroll down to polar alignment and press enter.  Scroll down to align mount.  Follow the menu.  Be sure you use the the azimuth and latitude screws to adjust to the final position. Hit enter and give it a try.

 

Before  the changes I was noticing a lot of movement  from sub to sub, even at 45 seconds.  After the changes virtually no movement at all.  I happened to try something a little crazy last night and tried 4 minute subs on M81, just to see if it was possible.  Here is a stack of 15 4 minute subs using the AVX unguided with the C6N reflector.  Its a step too far, but really good everything considered.

 

 

 

 

 

 

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#8 Gipht

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Posted 14 June 2017 - 03:50 PM

Forgot to mention one other thing. My AVX does not always turn the tracking on.  its hit and miss. I go ahead and turn the tracking on at the start just to be sure.


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#9 Stelios

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Posted 14 June 2017 - 04:25 PM

You should buy a guidescope and guidecam, regardless of what happens to your AVX. Guiding is the way to go in astrophotography, even with premium mounts (unless you have a 10Micron or an AP mount with precision encoders, which start at well over $10,000). I don't know why people resist it. It's not hard, it's not expensive, and it makes a huge difference. 

 

As to "what to buy" it almost doesn't matter. With your focal length of 750mm (a bit high for beginning AP, but not insanely so) a 50 or 60mm guide scope and a ZWO or QHY guide camera in the $200 range will do fine. Don't obsess over it, just get it. While it's being delivered, download PhD2 guiding (a free program and a near-universal standard) and read the "best practices" PDF. It's really simple enough that it works almost without you doing anything except specifying two parameters (focal length of guidescope and pixel size of guide camera) and connecting your AVX's handcontrol port to your computer. 

 

[Edit] You'll also need to download drivers for your guide camera and the Celestron ASCOM driver (from the ASCOM website). Easier done than said. [/Edit]

 

Incidentally, my AVX can't do 30 seconds unguided either, mainly due to DEC issues. For RA, you can simply record your periodic error and play it back (read the AVX manual, it outlines how) which will reduce the RA swings quite noticeably. 


Edited by Stelios, 14 June 2017 - 04:27 PM.

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#10 Genryuu111

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Posted 14 June 2017 - 11:03 PM

Wow, woke up and got so many nice replies, thank you everyone!

I actually tried most of what was suggested, just forgot about it when I posted yesterday..but let's go in order.

 

@einarin

The problem is that I could do way better than 30 seconds when I didn't know what I was doing (like I said, my crappy m27 had 2 mins subs), and the more I tried to make everything better, the worse everything got.

I use live view with my DSLR on my laptop to align. The movement (and sorry if I'm being very poor with terminology) is, if I have a 5 pixels star in the center of the reticle, it would move about 5 pixels in RA in the first 30 seconds-one minute, and then stop there for a while.

Since this is my first telescope and mount experience, I don't know what is normal and what is tolerable, but going from 2 minutes to 30 seconds really sounds weird to me.

 

@overnight
Yes, I know it was out of collimation, I didn't check it before imaging that night.

I already did a factory reset a few times, inbetween the many other things I tried. But I guess I'll do another one tonight, it won't hurt.

 

@SkyGibbon

Thanks for the inputs, another thing I missed to point out is that yes, I always end up moving usign up and right.

 

@Goofi
I'm not going to buy a comma corrector for a newtonian that basically came almost free with the mount tongue2.gif

I will probably upgrade the scope within the year, so for now I'll just bear with the coma.

Anyway, I guess I'll write down whatever happens from now on, in this thread.

 

@Gipht

Thanks for the recap!

 

1) Yeah, that is one thing I started being aware of. Actually, the DEC clutch would touch the motor below and open a little, while turning. I set it so that it's firmly closed in a position that doesn't touch the motor. But anyway, my problem is with RA..

 

2)I am on my balcony, on ground floor, so that's not an issue in this situation tongue2.gif

 

3)I will double check.

 

4)I will buy an actual level today (I was using my phone) and see if something changes.
 

5)Doing that already.

 

6)As I said, I tried both drift alignment and the ASPA. One thing that bugs me with ASPA is that it always makes me move everything a lot more than I would expect, especially in ALT (which should not even be changed at all since I'm always in the same spot). Anyway, since in the last days I've been focusing on drift alignment alone, I will give ASPA another chance, and see if I can get better results.

 

Very nice picture, I'm very far from getting something like that ahah

 

What do you mean with turning the tracking on? Anyway I don't think that's my problem, stars would drift way faster with the mount turned off.

 

@Stelios

Yes, I am going to buy a guidescope+camera in the next few weeks, I just don't have the money right now smile.gif

Thanks for the steps, I will do that.

 

Concerning what to buy, being in Japan I am very limited to what I can find, with a reasonable price.

I tried going to an astronomy store not far from where I live, and their "cheap" solution for a guide set was 600 bucks.

So, I'm probably going to go with these two, on Amazon, they're within my reach, but please correct me if they don't sound decent enough:

 

https://www.amazon.c...d=II8ED2WCZAKTO

60mm, F4

 

https://www.amazon.c...=I32NVELN1LQXQQ

Which would be this camera (I'm probably going to buy the B/W one, costs just 20 dollars more): https://www.firstlig...os01200kpb.html


Edited by Genryuu111, 14 June 2017 - 11:05 PM.


#11 Gipht

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Posted 15 June 2017 - 09:17 AM

If you go to the tracking menu,  then click on mode, before alignment.  Then, the tracking is turned off.  I turn it on to start.  It is supposed to switch on automatically when you do your alignment.  Mine does not always do that.  Like you say though, that would be very noticeable.

 

One other thing I do  that might help, is to spread the tips of the tripod legs slightly after the tripod is set down.  Any flex in the tripod results in error.  Some people build a second lower spreader on the tripod, similar to the eyepiece holder tray but a couple of feet lower.



#12 rmollise

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Posted 15 June 2017 - 10:19 AM

As you can see, everybody's experience is different. No AVX is the same.

Hardly the case. I have two buddies here with VXes, and their mounts perform pretty much identically to mine (fine guided up to at least 1400mm) despite having been purchased at different times years apart.

 

OP:

 

Work on collimation and polar alignment. ;)


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#13 overnight

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Posted 16 June 2017 - 11:07 AM

 

As you can see, everybody's experience is different. No AVX is the same.

Hardly the case. I have two buddies here with VXes, and their mounts perform pretty much identically to mine (fine guided up to at least 1400mm) despite having been purchased at different times years apart.

 

OP:

 

Work on collimation and polar alignment. wink.gif

 

Needs bigger sample size...



#14 xiando

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Posted 16 June 2017 - 11:23 AM

As Rod said, collimation and polar alignment. Your OTA is WAY out of collimation (and also likely could stand application of a coma corrector/field flattener.)



#15 dfisherows

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Posted 16 June 2017 - 11:47 AM

 

 

As you can see, everybody's experience is different. No AVX is the same.

Hardly the case. I have two buddies here with VXes, and their mounts perform pretty much identically to mine (fine guided up to at least 1400mm) despite having been purchased at different times years apart.

 

OP:

 

Work on collimation and polar alignment. wink.gif

 

Needs bigger sample size...

 

I've owned 5(maybe 6 lose count) over the years and only 1 was bad out of the box.  I have 2 right now and both track great and one of them tracks extremely well right out of the box from HPS.


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#16 Genryuu111

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Posted 16 June 2017 - 02:54 PM

I appreciate the inputs, but telling me to collimate my telescope when:

 

1-I already said I fixed that

2-I'm talking about a RA drift problem

 

is not going to help me in any way.

 

That picture was posted just to show that I could, out of luck, take 2 mins subs when right now all I can take are 30 seconds subs.

No amount of coma correction is going to fix a RA drift problem.

 

With drift alignment I manage to have stars stay still for 5-10 minutes in DEC, but they move a lot in RA, left and right.

I am pretty sure my problem is not polar alignment.


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#17 overnight

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Posted 16 June 2017 - 03:04 PM

The problem is the mount. The mount if polar aligned should be able to track well in DEC which it is. Drifting in RA is expected because theoretically its the only axis that needs to be pushed (its Theoretically, in real life that will never happen).

 

You can't expect a mount like the Advanced VX to be able to hold its own for 5-10 minutes in RA without guiding. If you want that, its tons of $$$. The only real way to solve your problem is guiding.

 

Basically, your expecting too much from an AVX.


Edited by overnight, 16 June 2017 - 03:06 PM.

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#18 rmollise

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Posted 16 June 2017 - 03:51 PM

I appreciate the inputs, but telling me to collimate my telescope when:

 

1-I already said I fixed that

2-I'm talking about a RA drift problem

 

is not going to help me in any way.

 

That picture was posted just to show that I could, out of luck, take 2 mins subs when right now all I can take are 30 seconds subs.

No amount of coma correction is going to fix a RA drift problem.

 

With drift alignment I manage to have stars stay still for 5-10 minutes in DEC, but they move a lot in RA, left and right.

I am pretty sure my problem is not polar alignment.

The reason people are telling you to look at your collimation is that it looks like it could still be off substantially. Might want to double check. 

 

If your stars move east/west, that's periodic error and is to be expected. If you have around 30" of movement, that's normal.

 

The AVX, and most mounts under the 7-10K+ range, will simply NOT work unguided at this focal length for five or ten minute exposures. Not hardly. You might get 30 seconds to a minute if you are lucky. 

 

wink.gif


Edited by rmollise, 16 June 2017 - 03:55 PM.

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#19 xiando

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Posted 16 June 2017 - 04:20 PM

The only DSO image you've provided is the only one I have to judge from. Your planetary aren't going to show me much that way. And the dumbell example shows severe coma, which is why I said something. My apologies. I thought you meant it when you said 

 

 

Any kind of advice is welcome, thanks in advance.

 

I've never learned to drift align, and yet even when I wasn't guiding I had relatively low drift, because I used a polar scope and carefully polar aligned the mount using it.

 

As far as guiders go, I'm using a modest 60mm aperture, 240mmfl guidescope I purchased from Astronomics about a month or so ago, which afaik is a Synta or GSO scope, so you *should be able to pick one or something similar up in your area (see link for identification/comparison) . I've had it running since June 2nd (five correction: four nights out... First was just a quick demo for myself as clouds rolled in quickly)  using an SBIG STI-C I bought back in 2012 as my primary camera, but there may be less expensive alternatives out there with larger camera FOVs and greater sensitivity than my STI (also, get a mono, not a color...higher functional spatial resolution) .

 

FWIW, after a few days out (four, to be specific), I'm guiding at about 1 arc sec. Nothing to write home to mom about but it's far better than before. And hopefully it'll get better as I actually learn how to use PHD Guiding.

 

Total cost, ~$140 for scope, ~$500 for the camera, but as I said there may less expensive options for guide cams. I think Atik and others (ZWO comes to mind) offer guide cameras in a t-thread format that cost around $400 or a little more and have about twice the pixel count and fov.

 

good luck.

 

edit: oh...one word of advise. I figured I'd leap frog and use an off axis guider. I recommend you don't start with one. They can be a real pain for those of us just getting into guiding. I stubbornly refused that advise when it was given to me, and now I have an OAG but don't use it (it's still mounted to my filter wheel but shut off with a flocked, threaded cap)


Edited by xiando, 16 June 2017 - 09:19 PM.


#20 Genryuu111

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Posted 16 June 2017 - 05:38 PM

@overnight and rmollise

I am not expecting go have 5-10 minutes subs, but as I already said, I went from being able to have 2 minutes subs, to barely being able to have 30 seconds ones.

 

But I guess the possible advices were already given, I will just wait next week when I'll be able to buy a guiding set, and hope for the best.

 

@xiando

Thanks for your tips.

The scope looks like the same I posted, just rebranded for the Japanese market :p

 

As for the camera, spending that amount right now is not an option sadly.

I will start with the one I found, and upgrade in the future if I feel I'll need it :)



#21 xiando

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Posted 16 June 2017 - 05:58 PM

No worries about the guide cam, I fully understand budget issues...(my STI-C was my ***main*** camera for over three years...)

 

Fwiw, a friend used a logitech QC 3000 for a while and it worked. I think he had to make or buy some extra box for  producing the pulses but it wasn't expensive. If that gives you an idea of what one can do when one must make do.


Edited by xiando, 16 June 2017 - 05:58 PM.


#22 overnight

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Posted 16 June 2017 - 07:42 PM

@overnight and rmollise

I am not expecting go have 5-10 minutes subs, but as I already said, I went from being able to have 2 minutes subs, to barely being able to have 30 seconds ones.

 

But I guess the possible advices were already given, I will just wait next week when I'll be able to buy a guiding set, and hope for the best.

 

@xiando

Thanks for your tips.

The scope looks like the same I posted, just rebranded for the Japanese market tongue2.gif

 

As for the camera, spending that amount right now is not an option sadly.

I will start with the one I found, and upgrade in the future if I feel I'll need it smile.gif

I wasn't saying 5 minute subs, I meant 5 minutes on the drift align...


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#23 Genryuu111

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Posted 18 June 2017 - 04:03 AM

@xiando

Yeah, I thought about that option too, but it's probably to cost me well enough to build one myself, that I'd rather buy a camera that can already do the job :p

 

@overnight
Oh I see :D

But anyway, it still puzzles me that I could take 2 mins subs without drift aligning the first time I tried, and now I get crazy drift every 30 seconds or so..



#24 overnight

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Posted 18 June 2017 - 12:24 PM

@xiando

Yeah, I thought about that option too, but it's probably to cost me well enough to build one myself, that I'd rather buy a camera that can already do the job tongue2.gif

 

@overnight
Oh I see laugh.gif

But anyway, it still puzzles me that I could take 2 mins subs without drift aligning the first time I tried, and now I get crazy drift every 30 seconds or so..

I'm pretty sure its polar alignment. You could have gotten it really good, and now it isn't so great.

 

How many nights have you tested it?

 

Have you gone out and consistently get the limit of 30 seconds? I can't tell from your original post.


Edited by overnight, 18 June 2017 - 12:30 PM.


#25 xiando

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Posted 18 June 2017 - 01:13 PM

Polar alignment is only one part of the equation. In equatorial mounted scopes, when  operating unguided,  balance also plays a part, as one circle of RA/DEC  will often produce stability and another will produce drift, even with a "well balanced" system...




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