Samibotss
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Posts posted by Samibotss
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Howdy,
I've been imaging the Eagle Nebula (M16) over the past few weeks, and I've encountered a problem concerning alignement accuracy as of recent. Simply put, on some nights I'll be able to get a decent alignement and have the mount find the object on the first try, and on others like tonight, using the same stars, the mount just doesn't seem to hone-in on the object.
It's strange, as I'll often test the accuracy after having done my 2-star alignement, and it finds objects like planets and bright stars relatively accurately (if only off-center), but fail to hone-in on M16. Unfortunately, I have a limited view of the night sky, and can only use stars in the south west - south east region, so I have a limited range of stars to be used for alignement, but even trying other stars doesn't seem to solve the problem.
Should I go for 3-star alignements? Is there something I can do to fix this? What's even more problematic is it seems sporadic, as if the mount wants to cooperate on some nights and doesn't on others.
Any help is appreciated
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10 minutes ago, michael8554 said:
Pretty basic PHD2 questions, sounds like you've not read any of the PHD2 Help and How To guides available via the PHD2 Help menu.
Such as
https://openphdguiding.org/phd2-best-practices/
Also if you start using EQMOD, don't get caught out by the default ASCOM PulseGuide Setting of 0.1, up that to 0.5 or more:
Indeed I have not, but I will now
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On 23/08/2021 at 09:22, Mctoot said:
I use the ASI120mm with the stock finder scope that came with my 200P-DS. I have tried to measure from the back of the scope (tricky while trying to hold my phone with the other hand!). In this case the C- adapter is not completely flush with the back of the scope - I estimate its around one turn in. I have not had remove the locking ring at the front of the scope to achieve focus . You can see from the EKOS guiding image that my stars are OK in the ASI120mm - I just managed to screenshot as the clouds rolled in - sorry (happy to provide a better shot when I next get out)
Anyway - I hope this is useful/helps!
On 17/08/2021 at 13:01, jacko61 said:According to the FLO website, your finderscope needs 18mm backfocus from the metal tube. As Michael stated above, the ASI120mm mini has 8.5mm from the sensor to the front of the fixed black ring so you need to add 9.5mm to that to get the correct backfocus. I also noticed a comment from one person on the FLo site that they had to remove the focus lock ring which was also mentioned above..
Sky-Watcher 9x50 Finderscope | First Light Optics
graeme
On 16/08/2021 at 21:18, michael8554 said:Without even looking at your GuideLog, I know realise the huge blob in your Saturday image is not a globular cluster, but an out-of-focus star, and what I thought were the stars are hot pixels.
So you have not "fixed the problem", the focus is still way out.
Take off the guidecam and focus the sun onto a flat surface.
Roughly measure from the back of the scope to that point.
That's where the ZWO sensor has to be located, it's 8.5mm inside the front of the camera with no adapters mounted,
Michael
Thank you all for the useful feedback
I've finally gotten clear skies & time to test it out, and indeed, I had to remove the locking ring. Ended up with sharp, pinpoint stars!
Guiding results are still abysmal, but I'm guessing it's because I'm missing a calibration to tell PHD2 where the scope is pointing, and I'm guiding on camera.
I'm gonna try EQMod Ascom guiding, to let PHD2 control the mount directly. I'm wondering if this will eliminate the need for a calibration, or the need for a recurring calibration?
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1 hour ago, Budgie1 said:
If you've screwed the front element in as far as it will go and you still can't get focus then you may have to try removing the front element locking ring.
Unscrew the front element and the locking ring, then screw just the front element back on to the finder. This will give you more thread and allow you to get the camera sensor and front element closer together. I had to do this on the same setup, but using the Celestron version of the 9x50. It does mean you can't lock the focus on the finder but it didn't seem to move that much when I was using it like this.
When you find focus, the stars will be pin point, you're still out of focus in that last PHD screen shot.
I'll definitely try this as well!
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1 hour ago, michael8554 said:
Without even looking at your GuideLog, I know realise the huge blob in your Saturday image is not a globular cluster, but an out-of-focus star, and what I thought were the stars are hot pixels.
So you have not "fixed the problem", the focus is still way out.
Take off the guidecam and focus the sun onto a flat surface.
Roughly measure from the back of the scope to that point.
That's where the ZWO sensor has to be located, it's 8.5mm inside the front of the camera with no adapters mounted,
Michael
I see. I'll try that and see what I get.
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On 14/08/2021 at 11:26, michael8554 said:
The info in your screen grab is limited.
Despite a 3 second exposure, Signal to Noise SNR is only 4.0, the yellow figure in the toolbar indicates it's of concern to PHD2.
If you move the blue slider to the left the display would show the stars better.
And if you displayed the Star Profile (Tools - Star Profile) we could maybe tell if that's a hot pixel or not.
(Though you are using the PHD2 Darks)
"Cal" on the toolbar is red, indicating either that the Calibration failed, or maybe you haven't tried yet - you did press the green button to make PHD2 Cal, and then guide ?
Post your PHD2 GuideLog, such as it is, so we can check your settings.
Michael
So, I've went out again last night, and despite having ajusted the focuser all the way, the stars still look blown out. I've tried doing the calibration by pressing the green button, but it doesn't seem to calibrate much.
Again, guiding on such blown out stars doesn't seem to be working out too well for me, I'm getting worse results than with no guiding
I've attached my PHD2 logs above.
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Well, I've completely pushed the focuser, and I think I've managed to fix the focusing issue. However, despite PHD2 finding a star, it doesn't seem to be guiding much. the crosshair is still brown, and since I'm guiding only with the camera, I can't do much in the of calibration. I can hear the mount seemingly trying to reajust when I turn on guiding, but I cant seem to push my exposure times beyond what I normally can achieve.
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2 hours ago, Clarkey said:
I have used the C adaptor with the SW finder and 120 mini and it is fine. I did have to wind the focused right to the end of its travel, but it did work.
ok I see, thanks for the insight
I'll try and reajust it
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1 hour ago, Cornelius Varley said:
Is this straight out of the box or have you attempted to change the focus by adjusting the front element of the finder ?
I have tried to adjust the front element, but there is little travel between the minimum and maximum positions. I'll retry tonight to see if I can get it to focus that way.
58 minutes ago, GoldTop57 said:Also is there a 1.25" extender included that you can screw into the front of the camera so it can sit further out of the scope?
I have screwed an included extender already, although it is quite small ( you can see the separation between the camera's black ring and the extender on the photos)
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Hello There!
I'm reaching out to you all regarding a recent acquisition of an Auto-guiding bundle, which includes a Sky-Watcher 9x50 Finder scope & ZWO Asi 120MM with C adapter.
The problem is, I can't seem to achieve focus on the (I think?) standard configuration. I'm looking to try my hand at guiding purely with the camera at first (no EQMod/ EQDirect), but since the stars look blown out, so PHD2 can't lock down and track anything. I've included images of both what I see in PHD2, and how my camera is attached to the finderscope.
I'm just wondering, if I need to buy an extension or if I'm missing something in the way it's setup.
Any input is appreciated
- Sami N.
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On 16/08/2020 at 17:21, vlaiv said:
That depends how your sensor is oriented. In both cases - south near meridian and west or east at DEC zero - you'll use RA motion and look for DEC drift.
If you orient sensor so that RA direction is in line with horizontal axis of sensor, then in both cases motion of the star will be left/right and drift will be up/down. In any other case - only one thing is sure - RA and DEC motion should be perpendicular to each other (if everything is ok and mount is orthogonal - and it should be).
Simplest way to orient sensor so that RA is horizontal is again to find bright star, start exposure and slew in RA - if line on exposure is horizontal - you are done, if not - rotate camera (for the same angle line is to horizontal on the image - but not necessarily in same direction - depends on how telescope inverts image) and repeat until line is horizontal.
On 15/08/2020 at 22:33, jif001 said:It’s normal for the mount to be inaccurate when it slews to the first target. You should always follow polar alignment with 2- or 3-star alignment. The latter assists the Goto system in finding the targets accurately. Pick a bright star some distance from the pole star and use the Goto to slew there. It will be off, but you use the handset buttons and finder scope to centre the star in the field of view, then tell the handset it’s there. Repeat with a second star somewhere else then, ideally, a third one. That should mean the Goto will be accurate finding your next target.
if you have a computerised setup using ASCOM, you can platesolve instead of centring the star each time, and sync the location to the mount.
4 hours ago, david_taurus83 said:Depends on focal length and exposure time. Even with perfect polar alignment, which is very hard to achieve btw, you will get some drift from periodic error and imperfections in the mounts running gear. The DARV method may be better but longer to set up. If it was me, I would select a spot in the garden and aim to setup in the exact same place each session. For example, I have drilled 3 small dents in the slabs in my back garden where the tripod sits. Each time I setup its just a case of setting the mount and tripod back out in the exact same spot by placing the tripod 'spikes' on the 3 dents. This gets me very close each time with little effort. Only small tweaks needed after though I can see Polaris.
If you could setup in a fixed spot, you could try the handset method to get you close and give imaging a go. If you still get star trails you could fine tune with the DARV method. But if you could mark the position where you were set up it would make future sessions much easier as you'd be very closely aligned to begin with.
I went out tonight to try out the DARV method, and this is the result I got :
Azimuth adjustements :
Altitude adjustment :
As it turns out, I can push to 8-10' exposure before seeing trails, which is better than before (4' max), but still not good enough. The problem I have is that the DARV method demands a 125 second exposure, but I can only push to 30' on my Canon 4000D. I don't know if that's good enough to correct the angle. I do have to say I moved along the DEC axis on the two adjustments, which may be wrong since I think I need to move on the RA for altitude.
As for the GoTo alignement, I think I have the good observation site settings, as on initial slew for 2-star alignement to the first star (Cebalrai) it was pretty close. However, for the second star, the handset kept showing me stars in the north western sky, which I cannot really see from my vantage point. I just did 1-star alignement with cebalrai, but despite an "alignement successful" message, it was inaccurate slewing to other targets, so I don't really know what to do here.
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20 minutes ago, david_taurus83 said:
Depends on focal length and exposure time. Even with perfect polar alignment, which is very hard to achieve btw, you will get some drift from periodic error and imperfections in the mounts running gear. The DARV method may be better but longer to set up. If it was me, I would select a spot in the garden and aim to setup in the exact same place each session. For example, I have drilled 3 small dents in the slabs in my back garden where the tripod sits. Each time I setup its just a case of setting the mount and tripod back out in the exact same spot by placing the tripod 'spikes' on the 3 dents. This gets me very close each time with little effort. Only small tweaks needed after though I can see Polaris.
If you could setup in a fixed spot, you could try the handset method to get you close and give imaging a go. If you still get star trails you could fine tune with the DARV method. But if you could mark the position where you were set up it would make future sessions much easier as you'd be very closely aligned to begin with.
I see, I was planning on doing the same once I got it properly aligned. Thanks!
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On 16/08/2020 at 18:21, david_taurus83 said:
In that case, the handset should have a polar align routine. I think its in utilities. You setup the mount and do a star alignment as normal. Then select the Polar Align function in the handset. The mount slews to a star of your choice. It prompts you to centre the star in an eyepiece with the controller. Once centred, it moves the star off centre and then prompts you to recentre by using the altitude and azimth knobs on the mount. Follow the handset prompts and it doesnt take long at all.
I did not know about that. Is it accurate enough for AP?
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Just now, vlaiv said:
That depends how your sensor is oriented. In both cases - south near meridian and west or east at DEC zero - you'll use RA motion and look for DEC drift.
If you orient sensor so that RA direction is in line with horizontal axis of sensor, then in both cases motion of the star will be left/right and drift will be up/down. In any other case - only one thing is sure - RA and DEC motion should be perpendicular to each other (if everything is ok and mount is orthogonal - and it should be).
Simplest way to orient sensor so that RA is horizontal is again to find bright star, start exposure and slew in RA - if line on exposure is horizontal - you are done, if not - rotate camera (for the same angle line is to horizontal on the image - but not necessarily in same direction - depends on how telescope inverts image) and repeat until line is horizontal.
Alright, I understand now. I'll definitely try this method once the skies clear up again. Thank you very much for all the insightful information
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2 hours ago, david_taurus83 said:
Do you have a Synscan handset?
Yes
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50 minutes ago, david_taurus83 said:
I think you need to also move the scope. Another option is the handset polar align if your mount has that function.
I haven't seen anything of the sort, but then again, I don't exactly know what "handset polar align" refers to
28 minutes ago, jif001 said:Check the settings in the handset, particularly the date. I think it uses the American format, where, for example, August 1st would be entered as 8-1-2020 (i.e. ‘August 1st’). If you entered it the other way around as 1-8-2020 (‘1st August’) the date will be 7 months adrift which might explain it going in the wrong direction.
I'm pretty sure I entered the date correctly, I did spot the fact it was using the american format.
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11 minutes ago, vlaiv said:
There are two places where you need to do above procedure. It has to do with X-Y coordinate system and projections and all that math stuff.
When you point your scope due south at celestial Meridian (or just before or after), any drift that happens in that part of the sky will be due to Polar alignment error in horizontal - or in azimuth.
So first step is to adjust your mount in azimuth by aiming at the star due south at meridian.
Second step is to do the same procedure aiming at eight east or west and DEC 0. Since this is 90 degrees to south - you are now doing alignment in altitude - or vertical.
This is why you need to have your mount level to begin with - only if mount is level you can "divide" adjustments like this so they are not dependent to each other.
DARV method says - start your exposure with telescope tracking and wait for 5 seconds. This little wait time is for star to "burn" a little reference dot at the beginning of the path. Then press your controller so that telescope slews at x1 speed in RA direction. Do that for half of "exposure" then reverse direction (just press opposite button) and hold for second part of exposure.
If you want to do 5 minute exposure without trailing - do above for 2.5 minutes in one direction and 2.5 minutes in other direction.
You can start by doing shorter runs - like 30seconds or one minute if your polar alignment is poor at the beginning, but as soon as you start improving it - switch to full duration of exposure.
Makes sense?
I think I understand, so the same procedure is done for altitude in regards to placing the star in the right hand side of the sensor, and going left and right?
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9 hours ago, david_taurus83 said:
^^^This!
9 hours ago, vlaiv said:Indeed, look at the post above by @Davey-T and follow that link - DARV is very simple and straight forward (and clever I might add) way to do "manual" drift align.
I would throw in a simple modification since you can't do regular polar align and then improve with drift.
Make your first couple of iterations shorter - about half a minute as drift is probably going to be significant. Later extend it to make polar alignment accurate.
Oh my, I completely missed his post. You're absolutely right, this looks a good solution to my problem. I just don't quite understand the last step with regards to the altitude, do I just take a 5sec exposure, see the trail, and adjust the altitude until I get it right, or do I also move the telescope during the exposure on the RA axis?
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1 hour ago, vlaiv said:
Long time ago, I drift aligned with a piece of software called EQAlign or something like that. Let me see if I can find it.
Here it is:
http://eqalign.net/e_eqalign.html
Unfortunately it requires WDM style drivers (like web camera) and I'm not sure you will find those for DSLR (you could - I've seen a piece of software that lets DSLR act as web cam for skype and such).
You don't really need software to do drift align. You can do it yourself by using long exposures and bright stars and judging trail that star makes due to drift (some sort of measurement of trail length). You need to orient camera so that you know which direction is DEC (vertical for example). There will be drift in RA as well - but you don't need to address that for polar alignment (but it can as well mess up your long exposures - check if PEC feature is available with your mount).
There is a limit to how much auto guider can fix things. Auto guiding works by using short exposures like second or two. It issues commands to mount to get to proper position - this is called pulse. Auto guiding software measures reference star position and determines how long this pulse should be to correct the position. It uses guide speed which is usually set to fraction of sidereal rate - x1 or lower like x0.25.
Sidereal rate is about 15"/s. This means that in theory, auto guiding can fix for drift that is 15"/s if set to operate on sidereal guide speed. In practice, you want your drift rate to be much lower than that as you don't want to correct each guide cycle - that also creates elongated stars - as mount moves back and forth all the time.
In reality - any decent polar alignment will have rather small drift rate. You can use this calculator to calculate drift rate due to polar alignment error:
http://celestialwonders.com/tools/driftRateCalc.html
I see, thanks for all the information! I'll try drift alignement manually then, and see how it goes. If it goes well, I'll start looking into autoguiding to improve my performance.
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9 hours ago, david_taurus83 said:
Hi. It might help if you can list your equipment, mount, scope, camera etc
SkyWatcher EQM35-PRO with Evostar 72ED, Canon 4000D.
9 hours ago, vlaiv said:Drift alignment method works with both guide scope / camera and primary scope camera - it is just a matter of convenience which one you'll use.
For good drift alignment and general goto precision, it is important to have your mount tripod - level and stable (not moving).
Auto guiding will correct for polar alignment errors, but it can't work miracles. The better your polar alignment is from the start - less work auto guider needs to perform. There is only one case where you don't want perfect polar alignment - if your mount has DEC backlash. In that case it is better to have slight polar alignment error which then causes DEC error to be to one side only (due to drift). Auto guider will correct this error and corrections will always be to one side as well. This prevents changing of direction in DEC and circumvents any issues with DEC backlash. PHD2 has algorithm called "resist switch" - and I think it is default DEC guiding algorithm. It is used precisely for this reason - small PA error is going to produce drift to one side only - everything else is either seeing or wind or mount roughness.
Is there a piece of software which would help me drift align with my DSLR? I think I saw somewhere that PHD2 doesn't currently support DSLRs. As for autoguiding, is there a limit to how much the auto guider can correct?
46 minutes ago, jif001 said:It’s normal for the mount to be inaccurate when it slews to the first target. You should always follow polar alignment with 2- or 3-star alignment. The latter assists the Goto system in finding the targets accurately. Pick a bright star some distance from the pole star and use the Goto to slew there. It will be off, but you use the handset buttons and finder scope to centre the star in the field of view, then tell the handset it’s there. Repeat with a second star somewhere else then, ideally, a third one. That should mean the Goto will be accurate finding your next target.
if you have a computerised setup using ASCOM, you can platesolve instead of centring the star each time, and sync the location to the mount.
Well, it wasn't just inaccurate, it was slewing in the opposite direction almost, and I had the "RA Offset > 45 deg" error. I think I'm slowly getting it right though, last time it slewed near enough to have the "alignement successful" message once I centered it, but it was inaccurate slewing to other targets after this, but that maybe do to the fact that I had only done a 1-star alignement with big adjustements.
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Howdy,
I've been getting familiar with my astrophotography recently, but I still have one problem remaining : Polar Alignement. The way I'm setup, I only have access to the southern part of the sky. Until now, I've used some methods to do it roughly with a compass, but that is nowhere near accurate enough for AP. The most exposure time I've gotten out of it before having trails is about 4 seconds. I'm now looking into doing drift alignement, and I was wondering, is an autoguiding scope required to do it? Until now all the information I found about it mentioned using a guide camera and PHD2. Another question I had is, since the autoguiding setup corrects for tracking errors, could it compensate for a rough polar alignement, or do you need a good one from the start?
Also, I have a slight problem with the Goto handset, as on initial alignement, it slews nowhere near the target, I think it must be the way it calculates Sidereal time. I've tried a bunch of different observation site settings, but I still can't get it right...
I would greatly appreciate if anybody can answer my questions
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1 hour ago, michael8554 said:
I think the cable swap shows the RA motor is faulty.
Any way you can tell if RA is jammed? Is there very slight play if you gently rock RA ?
Michael
There doesn't seem to be any play, I do note that the gears just don't move at all, and don't produce any noise, it's as if the motor is completely dead
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16 hours ago, michael8554 said:
Well I would leave it tracking for 10 minutes or so to see if RA is tracking but not slewing.
Try replugging so that the working Dec electronics are driving RA, and vice versa.
But if it's new and not working I would return it, opening it up will invalidate the gaurentee.
Michael
It doesn't seem to track, I left for a while and was still in the same position RA-wise.
Inverting the wiring for DEC and RA does nothing.
I'll probably end having to return it, but if it can be fixed by just replacing the motor, or if I can somehow make sure it's not the handset (it probably isn't since it doesn't track anyways), that would be nice.
Thanks for your input!
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38 minutes ago, michael8554 said:
Is this a new mount you are operating for the first time? Faulty mount or handset.
Is the RA motor able to track?
Does RA slew at the slowest setting?
Does the power LED on the mount go out when you try RA slews?
Probably the power supply isn't powerful enough, spec may be 3A but may not be true.
New mount indeed.
I didn't do any tracking test, I assume it wouldn't seeing as though it doesn't move. I tried manually moving the it along the RA axis, and then parking it to the home position, but again, only DEC slewed.
I tested different rates, but it doesn't seem to slew in any of those, as the gears are immobile.
I don't see any power LEDs on the mount, I wasn't aware there was one.
As for the power supply, I also tested it by plugging it into my car with the supplied cigarette lighter cable, and the same problem occured.
At this point I'm wondering whether I can simply replace the faulty motor, or even maybe open it up to see what happens when I try to slew. If the handset is the faulty component here, I don't know how I would go about testing that out. I don't have a lynx cable for EQMod, and I don't have the hardware required to update the handset's firmware.
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Alignement accuracy inconsistency with SkyWatcher EQM-35 PRO GoTo
in Discussions - Mounts
Posted
I didn't know I could do multiple alignements, I always thought doing an alignement would wipe the previous one's data. I'll try doing 2-star + 1-star and see if it improves result.
As for platesolving, I just never took the time to learn it and understand it, will surely check it out now that you mention it
Yeah I thought of it as well, so I parked and restarted the mount, but alignement was still off...