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Unguided exposures with an EQ6-R

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#1 Bokchoy Ninja

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Posted 21 May 2019 - 05:35 PM

Hello,

I'm just starting out with an EQ6-R and an ES 80mm Triplet (480mm focal length). After polar-aligning my mount, I'm only getting 30 second exposures before I see significant streaking (of M101, which is quite close to Polaris).

 

Granted, my polar alignment is a bit rough since I'm rotating my RA axis until I think the polarscope reticle is in a plus-sign orientation (with the counterweight straight down the reticle has a rotation offset). This introduces a small error that might affect the tracking.

 

I know that an option is to use the syscan polar alignment procedure, but this requires multistar alignment which needs stars near the horizon (and I'm on the patio where my FOV is limited).

 

How long of unguided exposures can I expect with this mount/scope when I have perfect polar alignment? 30 seconds seems really short.


Edited by Bokchoy Ninja, 21 May 2019 - 05:36 PM.


#2 David_Ritter

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Posted 21 May 2019 - 05:43 PM

If you cannot get good polar alignment, then 30 seconds or so is probably the best unguided performance that you can realistically expect.

 

Under similar conditions (but with a less capable mount) I was never able to get good exposures longer than about 20 seconds.

 

Unguided imaging requires nearly perfect polar alignment. Any alignment errors, however small, will cause the mount to drift. The larger the error, the faster it will drift.

 

 

 


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#3 Bokchoy Ninja

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Posted 21 May 2019 - 05:47 PM

If you cannot get good polar alignment, then 30 seconds or so is probably the best unguided performance that you can realistically expect.

 

Under similar conditions (but with a less capable mount) I was never able to get good exposures longer than about 20 seconds.

 

Unguided imaging requires nearly perfect polar alignment. Any alignment errors, however small, will cause the mount to drift. The larger the error, the faster it will drift.

Thanks for the reply. I don't really have a sense for what "good" polar alignment is. I'm trying hard to put polaris where it should be -- biggest weak point seems to be the orientation of the reticle, which I'll try to get more accurate using a pole as a reference and marking the RA orientation.

 

Given that I'm still in my return period for the mount, the biggest thing for me is just making sure I don't have a dud. But it sounds like what I'm getting is typical.


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#4 David_Ritter

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Posted 21 May 2019 - 06:03 PM

From the sounds of it, your mount is probably ok.

 

And your alignment methodology may be a bit rough, but it's still basically sound. For visual use, it should work well and if you were auto-guiding, you'd probably be getting good images too.

 

When I was using my EQ6 for imaging, I used to do exactly what you were doing. I'd set it up with the polar scope and basically eyeball it as best I could.  Then I'd do the basic 2-star alignment from the hand controller.

 

But after that I'd also follow up using the polar alignment built into the hand controller. Even though I could not get stars on the horizon, the hand controller still offered several stars that I could see. So I was able to do the procedure. And it worked too, after that mount usually drifted a lot less.

 

Still though, for long exposure imaging, you probably will need to auto-guide at some point. I've used a few different mounts now, and every single one, even the higher end ones, all benefit from auto-guiding.

 

Oh, and I also recall that the EQ6 had a procedure for calibrating the polar scope. It involved rotating the mount in RA and adjusting the set screws on the polar scope so that the middle cross hairs stayed exactly centered. That helped a lot for getting the initial polar alignment pretty close. So if the EQ6-R has a similar calibration procedure, that may help too.



#5 Bokchoy Ninja

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Posted 21 May 2019 - 06:15 PM

From the sounds of it, your mount is probably ok.

 

And your alignment methodology may be a bit rough, but it's still basically sound. For visual use, it should work well and if you were auto-guiding, you'd probably be getting good images too.

 

When I was using my EQ6 for imaging, I used to do exactly what you were doing. I'd set it up with the polar scope and basically eyeball it as best I could.  Then I'd do the basic 2-star alignment from the hand controller.

 

But after that I'd also follow up using the polar alignment built into the hand controller. Even though I could not get stars on the horizon, the hand controller still offered several stars that I could see. So I was able to do the procedure. And it worked too, after that mount usually drifted a lot less.

 

Still though, for long exposure imaging, you probably will need to auto-guide at some point. I've used a few different mounts now, and every single one, even the higher end ones, all benefit from auto-guiding.

 

Oh, and I also recall that the EQ6 had a procedure for calibrating the polar scope. It involved rotating the mount in RA and adjusting the set screws on the polar scope so that the middle cross hairs stayed exactly centered. That helped a lot for getting the initial polar alignment pretty close. So if the EQ6-R has a similar calibration procedure, that may help too.

Thanks for the reply! I'll definitely go into autoguiding as soon as I can afford it -- just trying to stretch my unguided exposures to the ~2 minute mark, which seems reasonable given other peoples' experience. I'll try some things to improve the polar alignment procedure -- I'm surprised that I'm so far off given that I'm basically doing everything right.



#6 jdupton

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Posted 21 May 2019 - 06:22 PM

Bokchoy Ninja,

 

   Since you are asking about getting very good polar alignment for some unguided imaging, I would suggest you you do your very rough polar alignment and then do a photographic drift alignment. One popular method is the so-called DARV method although you can find other names and slightly different version written up on the Web. The DARV method is described pretty well here on Cloudy Nights. Check out this link:

 

https://www.cloudyni...bert-vice-r2760

 

   After you have done this a few times, you can reduce declination drift to a very small amount. You will always have RA back-and-forth drift due to PE. That must be guided out as no amount of exact polar alignment will help you there.

 

   To determine the amount of polar alignment error you are seeing, go to the following page and plug in the numbers from one of you imaging sessions. It can report the alignment error given the target, drift amount in arc-seconds, and amount of time for that drift to happen.

 

http://celestialwond...rErrorCalc.html

 

   After using the calculator and improving your alignment, you will get a feeling for how long you mount should be able to go unguided. Then you can start to estimate how much time to put into drift aligning for meeting your goals.

 

 

John


Edited by jdupton, 21 May 2019 - 06:23 PM.

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#7 nimitz69

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Posted 21 May 2019 - 06:51 PM

I have this mount and before I was guiding I could get up to 2 min subs.  The key is that you’ll need to download their PA App.  It’s called ‘PS Align”, then follow the direction exactly and you’ll get very precise manual PA.  Make sure you also read and follow the calibration procedure before you follow the PA procedure or you’ll never get a precise alignment.  Ignore the orientation of the the scope’s reticle, it is never installed to be vertical and it doesn’t matter, the cal procedure in the App will take care of that for you.  Also ignore the etching of the Big Dipper, it’s meaningless.

 

my first few times using SharpCap pro & my guidescope and camera to do PA I did a manual PA using the App first and I was always within 30” or less before performing the PA using SharpCap s/w.



#8 TelescopeGreg

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Posted 21 May 2019 - 06:55 PM

Thanks for the reply. I don't really have a sense for what "good" polar alignment is. I'm trying hard to put polaris where it should be -- biggest weak point seems to be the orientation of the reticle, which I'll try to get more accurate using a pole as a reference and marking the RA orientation.

 

Given that I'm still in my return period for the mount, the biggest thing for me is just making sure I don't have a dud. But it sounds like what I'm getting is typical.

If you have a smartphone, look for a Polar Alignment app that will tell you where Polaris should be in your polar scope.  On my Android phone, I use "PolarisView".  Be sure to understand whether it's giving you the view through the scope or the real sky, as the scope's view will be inverted. 



#9 kathyastro

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Posted 21 May 2019 - 07:00 PM

Granted, my polar alignment is a bit rough since I'm rotating my RA axis until I think the polarscope reticle is in a plus-sign orientation (with the counterweight straight down the reticle has a rotation offset). This introduces a small error that might affect the tracking.

That sounds like your problem.  The correct orientation of the polar scope reticle changes continually with time.  Since the orientation moves at sidereal rate, if you align at the same time every night, the orientation should be different every night.  Through the course of a year, the correct orientation will move through 360 degrees.

 

So either use one of those polar scope orientation apps, or use the Polaris HA information provided by your handset and the RA setting circle to set the correct orientation.

 

Setting the polar scope to the wrong orientation for the date and time will result in a polar alignment error of anywhere up to 1.5 degrees.



#10 Bokchoy Ninja

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Posted 21 May 2019 - 07:23 PM

I have this mount and before I was guiding I could get up to 2 min subs.  The key is that you’ll need to download their PA App.  It’s called ‘PS Align”, then follow the direction exactly and you’ll get very precise manual PA.  Make sure you also read and follow the calibration procedure before you follow the PA procedure or you’ll never get a precise alignment.  Ignore the orientation of the the scope’s reticle, it is never installed to be vertical and it doesn’t matter, the cal procedure in the App will take care of that for you.  Also ignore the etching of the Big Dipper, it’s meaningless.

 

my first few times using SharpCap pro & my guidescope and camera to do PA I did a manual PA using the App first and I was always within 30” or less before performing the PA using SharpCap s/w.

Thanks for the advice. I would like to download this app but it doesn't seem to be available on my android phone. Is there anything equivalent that is available for android?



#11 Bokchoy Ninja

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Posted 21 May 2019 - 07:25 PM

That sounds like your problem.  The correct orientation of the polar scope reticle changes continually with time.  Since the orientation moves at sidereal rate, if you align at the same time every night, the orientation should be different every night.  Through the course of a year, the correct orientation will move through 360 degrees.

 

So either use one of those polar scope orientation apps, or use the Polaris HA information provided by your handset and the RA setting circle to set the correct orientation.

 

Setting the polar scope to the wrong orientation for the date and time will result in a polar alignment error of anywhere up to 1.5 degrees.

So just to clarify... The image on my Polar Finder app has polaris located on a crosshair and the crosshair is aligned to a "plus" sign. When I look through my polar scope, the crosshair is crooked. So I rotate it until it is plus-sign shaped and then position polaris to the spot indicated by the app.

 

Is this wrong?



#12 OldManSky

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Posted 21 May 2019 - 07:50 PM

So just to clarify... The image on my Polar Finder app has polaris located on a crosshair and the crosshair is aligned to a "plus" sign. When I look through my polar scope, the crosshair is crooked. So I rotate it until it is plus-sign shaped and then position polaris to the spot indicated by the app.

 

Is this wrong?

No, that's right.  :)



#13 durak

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Posted 21 May 2019 - 07:51 PM

Thanks for the advice. I would like to download this app but it doesn't seem to be available on my android phone. Is there anything equivalent that is available for android?

The PolarFinder app is great. I use it with my eq6-r. On the very first night out, with the same scope as you, using only the PolarFinder app for alignment, I was able to get 3 minute unguided shots with no trailing whatsoever. 

 

See below for my picture from that night (not the greatest image ever but the tracking was spot on):
 

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#14 Bokchoy Ninja

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Posted 21 May 2019 - 07:54 PM

The PolarFinder app is great. I use it with my eq6-r. On the very first night out, with the same scope as you, using only the PolarFinder app for alignment, I was able to get 3 minute unguided shots with no trailing whatsoever. 

 

See below for my picture from that night (not the greatest image ever but the tracking was spot on):
 

Excellent image, thanks for sharing your experience.

 

I'll use that as a benchmark for my mount, then. If I can't get anywhere near that, I'll assume something's fundamentally wrong with my mount.

 

Did you do a multi-star alignment?



#15 Bokchoy Ninja

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Posted 21 May 2019 - 08:15 PM

The PolarFinder app is great. I use it with my eq6-r. On the very first night out, with the same scope as you, using only the PolarFinder app for alignment, I was able to get 3 minute unguided shots with no trailing whatsoever. 

 

See below for my picture from that night (not the greatest image ever but the tracking was spot on):
 

By the way, is your bubble level accurate? I find mine to be way off comparing it to my phone's bubble-level app set on the tripod.



#16 durak

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Posted 21 May 2019 - 08:59 PM

Excellent image, thanks for sharing your experience.

 

I'll use that as a benchmark for my mount, then. If I can't get anywhere near that, I'll assume something's fundamentally wrong with my mount.

 

Did you do a multi-star alignment?

I used the app and then did a two-star alignment.



#17 durak

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Posted 21 May 2019 - 09:00 PM

By the way, is your bubble level accurate? I find mine to be way off comparing it to my phone's bubble-level app set on the tripod.

I have only been out 3 or 4 times. I have not bothered to check my bubble level against anything else. That's probably a good thing for me to do though so thanks for the reminder.



#18 nimitz69

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Posted 21 May 2019 - 09:34 PM

Thanks for the advice. I would like to download this app but it doesn't seem to be available on my android phone. Is there anything equivalent that is available for android?

Unknown.  I’d contact Skywatcher and ask them, they were the ones who recommended that App to me to do PAs ...



#19 Pawan

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Posted 21 May 2019 - 10:22 PM

Since you have a camera attached to your telescope, you can use Sharpcap to get a really good Polar Alignment. It makes Polar aligning trivial.

Visual reticle alignment method will not cut it no matter what you do if you are not guiding. Also, since you are not guiding, make sure the mount is level.

#20 Bokchoy Ninja

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Posted 21 May 2019 - 11:16 PM

Since you have a camera attached to your telescope, you can use Sharpcap to get a really good Polar Alignment. It makes Polar aligning trivial.

Visual reticle alignment method will not cut it no matter what you do if you are not guiding. Also, since you are not guiding, make sure the mount is level.

Does that work with DSLRs?



#21 Bokchoy Ninja

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Posted 21 May 2019 - 11:18 PM

I have only been out 3 or 4 times. I have not bothered to check my bubble level against anything else. That's probably a good thing for me to do though so thanks for the reminder.

Well, I realized I had the "diagonal" viewing option enabled on my polarfinder app, instead of "telescopic". So the view I was getting had the cross-hair flipped vertically and I had polaris placed wrong by 4 "hours". 

 

Can't wait until the weather cooperates so I can get out there and see if I can match your 2 minute subs!

 

By the way, are you using a field flattener? 


Edited by Bokchoy Ninja, 21 May 2019 - 11:19 PM.


#22 17.5Dob

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Posted 21 May 2019 - 11:37 PM

Hello,

I'm just starting out with an EQ6-R and an ES 80mm Triplet (480mm focal length). After polar-aligning my mount, I'm only getting 30 second exposures before I see significant streaking (of M101, which is quite close to Polaris).

 

How long of unguided exposures can I expect with this mount/scope when I have perfect polar alignment? 30 seconds seems really short.

Yes 30-45" is correct, even with perfect PA.....for 100% usable subs.

That's why everyone autoguides



#23 kathyastro

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Posted 22 May 2019 - 06:19 AM

So just to clarify... The image on my Polar Finder app has polaris located on a crosshair and the crosshair is aligned to a "plus" sign. When I look through my polar scope, the crosshair is crooked. So I rotate it until it is plus-sign shaped and then position polaris to the spot indicated by the app.

 

Is this wrong?

That description is unlike any polar scope reticle I have seen.  It doesn't sound right, but I will defer to someone who is familiar with that design.

 

[EDIT] OK, I didn't recognize the reticle from the description, but I have looked it up, and it is similar to my iOptron.  Yes, it sounds like you are probably doing it right.  The reticle has to be oriented correctly, with zero at the top and the primary cross-hairs oriented vertically/horizontally.  Then you position Polaris where the app says to position it.

 

Done accurately, you should be able to get 60s - 120s exposures without trailing, especially with a short focal length scope.


Edited by kathyastro, 22 May 2019 - 06:52 AM.


#24 durak

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Posted 22 May 2019 - 09:06 AM

Well, I realized I had the "diagonal" viewing option enabled on my polarfinder app, instead of "telescopic". So the view I was getting had the cross-hair flipped vertically and I had polaris placed wrong by 4 "hours". 

 

Can't wait until the weather cooperates so I can get out there and see if I can match your 2 minute subs!

 

By the way, are you using a field flattener? 

I use the Orion 0.80x reducer.  I bought it on the recommendation of a member here at CN. It seems to work very well and it is one of the less expensive reducers/flatteners for small refractors. 

 

https://www.telescop...ASABEgIS_fD_BwE



#25 Bokchoy Ninja

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Posted 22 May 2019 - 09:26 AM

I use the Orion 0.80x reducer.  I bought it on the recommendation of a member here at CN. It seems to work very well and it is one of the less expensive reducers/flatteners for small refractors. 

 

https://www.telescop...ASABEgIS_fD_BwE

Right on.

I have the Hotech flattener (no reduction) and it also works well.




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