# 24 Sep, 2019 17:04
|I have been struggling with trying to figure out how to do drift alignment corrections and I am failing miserably!!! I live just 2 degrees north of the Equator and I do not have a view of either of the Celestial alignment stars therefore, after a rough polar alignment using a compass and bubble level I try to perform drift corrections with an Eastern star but here is where I am getting totally lost! East? West? North, South, position the cross hairs in the eyepiece??? I have managed to get there once or twice by accident and I don't even know how I did that so, does anyone out there have source for teaching the brain dead how to properly correct for less than accurate polar alignment? FYI: I have pretty exhausted the sources on you tube.|
# 24 Sep, 2019 17:35
I hate to suggest throwing money at the problem but I believe Polemaster works in the Southern hemisphere. It might be worth contacting them about your situation.|
Drift alignment is just time consuming and difficult. I do it for a final fine tune sometimes but I wouldn't want to rely on it as my primary method.
# 24 Sep, 2019 18:15
John TuckerThank you for the reply, it is my understanding that one must be able to see either of the celestial alignment stars for the Polemaster to work, the new version of the ASI Air also offers a precise polar alignment feature however it to requires a view of the pole stars. My next experiment will be with Sharpcap however that requires windows and I am a diehard Mac user who is thinking that he is about to die
# 24 Sep, 2019 22:12
|You can use the drift alignment tool in PHD 2, it´s pretty straight forward and you can use it with your Mac.|
# 24 Sep, 2019 23:05
|sharpcap have polar tool too,it really works well.|
# 24 Sep, 2019 23:22
I second this suggestion: I can't see the celestial pole from my place, but I get a good polar alignment using the Drift Align routine in PHD2. It's a little tedious but simple enough and extremely accurate.
# 25 Sep, 2019 04:37
Do this and you will be fine. I do great polar alignment with the crappy wedge on my meade ETX-125. I get zero north / south drift.|
# 25 Sep, 2019 07:38
UN73I do have PHD now so I will give this a go, thank you for the suggestion.
# 25 Sep, 2019 07:39
HeathenStarHunter623This looks like a great tutorial, once I get through it and make a few practice runs I will report back to this post. Thank you.
# 25 Sep, 2019 08:39
Roman PierceHeathenStarHunter623This looks like a great tutorial, once I get through it and make a few practice runs I will report back to this post. Thank you.
You´d need a view on Polaris and Kochab for this method…
# 25 Sep, 2019 11:50
|Phd2 drift alignment is precise and easy. Would never use anything else even if I would have polaris in sight.|
# 25 Sep, 2019 14:17
UN73Uggggh, I have not read the tutorial yet, thanks for the heads up !Roman PierceYou´d need a view on Polaris and Kochab for this method…HeathenStarHunter623This looks like a great tutorial, once I get through it and make a few practice runs I will report back to this post. Thank you.
# 25 Sep, 2019 14:20
MarcCurrently trying to get there, PHD is installed but does not see my AVX mount Still troubleshooting… Indigo Server says the mount is connected but PHD neither sees it or can be pointed to it but I think that is for another forum?? Looks like a few more loooooooong nights of horrible drift corrections for this imager?
# 25 Sep, 2019 16:53
Using my macbook bootcamped win10 and ascom so sadly I have no idea about Indi yet.|
Maybe you find an answer in this thread: https://www.cloudynights.com/topic/656717-phd2-ain’t-no-graph/
# 25 Sep, 2019 17:19
Hi Roman, it is not that hard as suggested above. Steps are:|
1. Get your finder well aligned with the view through your illuminated reticle eyepiece. You could add a Barlow, as long as reasonably bright stars do not dim too much in the view.
2. Find a reasonably bright star near south, close to the celestial equator and put it in the crosshairs. (Obviously, you are now running your RA motor at sidereal rate to follow that star.)
3. Make sure your crosshairs are parallel to the North-South and East-West direction by moving your scope and rotating your illuminated eyepiece.
4. Put the star in the crosshairs and take a few sips from a beverage of your choice, then check again after a few minutes.
5. If the star moved up (North), you need to turn your mount east using the azimuth knobs at the bottom of your mounthead. Turn it west, if the star moved down (South). Ignore any east-west motion; it doesn’t matter.
6. Put the star back in the cross-hairs (this is where a properly alignes finder is crucial!) and
repeat this until up/down motion is negligible.
7. Find a star fairly close to the eastern horizon (within say 15-20 degrees) and agaim close to equator if possible. Again put it in crosshairs, make sure you crosshairs align with N/S and E/W motion of scope.
8. Same analysis, but now if star moves up (North), reduce the angle of the mount w.r.t. Northern horizon by turning it down with the altitude adjustment knobs at the base of the mount head. If the star moves down (South) increase the angle by turning your mounthead more. Repeat until up/down motion becomes negligible in say 5 minutes.
9. After this, you could repeat the procedure for azimuth eith a southern star again to make sure it wasn’t messed up too much, but if you are careful and take it slow with the altitude knobs, you should be OK.
10. Find a refill for empty beverage holder.
# 25 Sep, 2019 18:03
|Victor, many thanks for taking the time to write out these instructions! I can see where I am making my mistakes…pretty much steps 3 through 9, number 10 I have down pat! Now time to puts steps into practice.|
# 26 Sep, 2019 01:47
|I used to have serious problems with ADV mount to n Chile in 2010-13, Celestron had glitches in their software, but since updated. ADV has a nice feature: all star allignment, you do not need Polaris view. I would suggest PD 2 drift allignment or Polar Master, bith methods are fine. I personally still use pokar scope and Iphone app for allignment, pretty good. Clear skies|
# 26 Sep, 2019 05:12
|Adel: I'm not convinced that Celestron's All Star Alignment works well enough for Astrophotography? I have been using this feature regularly in my efforts to learn and the results are that I still see star drift in my imagery, I do like the idea of using PHD or Sharpcap though I still have not sorted out the connectivity issue I am having with that those applications. Another reality I have witnessed is that even if I shorten my exposure time to 30 seconds, I will see image shift with every exposure indicating that the telescope is not operating within the same rotation as the stars. This Drift Method of alignment is sort of an obsession for me, I want to get this right. Thank you for your suggestions.|
# 26 Sep, 2019 05:27
It can be difficult to do polar alignment when near the equator. For one thing some Mounts have a minimum elevation. Here are the first steps, which I didn't see mentioned above, your Mount needs to be set pointing north and it is important to look up and correct for the deviation between true north and magnetic north. The elevation of the Right Ascension axis should be equal to your latitude. So for you it needs to be set to 2 degrees, so the Right Ascension axis will almost be horizontal. Make sure your Mount has this capability.|
If you then follow the steps outlined by Victor above, you should have no trouble. If you get the direction of adjustment wrong, you will see the drift gets worse, so just go back the other way.
Whilst it can be time consuming, it is reliable if you don't have the access to or choose not to use the other methods mentioned. I also believe it is a good method to master first, before moving on to other methods. I quite enjoy doing it from time to time.
If you really want to go into it more I have a spreadsheet where you can enter the drift rate which will calculate how many turns on which knobs to allow you to get there a bit quicker.
# 27 Sep, 2019 06:21
As someone who has very recently learnt how to drift align from a location with no clear view of the pole (southern, in my case), a few random comments:|
1. I've gone from an hour of stuffing around to 5-10 minutes for near perfect polar alignment.
2. Given you have a ZWO camera and a laptop, you would be crazy in my view to do anything other than use the 'drift align' process in PHD2. You can do it using a visual eyepiece, but why bother when you have PHD2 there ready to give you an easy to understand graph and recommended adjustments.
3. You do not need ASCOM (etc) control of your mount - you can do 'dumb' drift alignment in PHD2, it's just a little bit more fiddly. That said, if you can get ASCOM set up then it's well worth it (amongst other reasons - it will correct the axis you are not currently aligning to remove any error from it, and it will slew to optimal locations for drifting).
4. In simple terms, the process in PHD2 is little more than:
(a) slewing to the appropriate spot (high for RA, fairly near the east or west horizon for DEC)
(b) hitting 'drift'
© watching the graph to see which way the relevant axis is heading and the total alignment error
(d) once the graph is stable (as in, the angle of the tracking line isn't changing much), hitting 'align' and then tweaking the relevant axis on your mount
(e) go back to (b) and repeat with tweaks to the physical alignment of your mount until your alignment error is close to zero and the graph close to flat
(f) go back to (a) and repeat for the other axis
5. I have found that it is very important to get your mount absolutely level. If you don't, then when you adjust one axis you will throw the other one out slightly.
6. If you get your mount perfectly level, then you will most likely only need minor DEC adjustments in future (I basically don't need to adjust DEC when I align).
7. If you wanted to do step 4 above but without PHD2, I found the most efficient options were either doing it visually with a high magnification eyepiece through my main scope, and getting a star right on the edge of the FOV (so that you can clearly see whether it's moving 'up' or 'down' because it will pop out of sight) or by doing it through a camera (e.g. a DSLR with live view zoomed right in). Pretty much, for fine adjustments you want to have as much magnification as possible to accentuate the drift.
8. If using PHD2 you want 'drift align' not 'polar drift align'.
9. No way is the built in computerised 'alignment' on a mount going to be good enough for photography IMHO. That function is useful for finding objects but not for polar aligning - IIRC it is basically giving the mount an orientation for its computerised map, not doing anything useful for polar alignment. What you want is sidereal tracking coupled with really good polar alignment (my best was 2 minute subs like this) or else full tracking.
10. Proper tracking via ASCOM and PHD2 makes life a million times easier because you just need adequate, not perfect, polar alignment anyway.
# 27 Sep, 2019 13:54
|Greetings Naill and thank you for the reply. Yes I do understand the points you called out. Magnetic Declination here happens to be 0 degrees which makes using a Mag compass pretty straight forward. I did run into the problem you mentioned regarding limits with mounts, in my case the AVX mount has its design limits at 7 to 77 degrees. To combat this I use a stack of MUCH smaller counter balance weights and also, I lower the front two tripod legs by a few degrees and then add those back with the Altitude adjustment for example. My latitude is 2.4 degrees North, I lower the tripod legs to to where 2.4 actually reads as level and then I add those degrees back with adjustments, end result is 5 degrees. In practice this seems to work out correctly. My specific problem was knowing which way to set the cross hairs in the eyepiece, was that North and South when looking through the eyepiece or actual North and South as we see it on Earth? I'm still not 100% clear on this. And then there are the corrections, I kept finding myself going in circles and always ending up right where I began and with the same exact star drift. I was going Mad!!! A spreadsheet for drift adjustments? Absolutely, I would love to see that if for no other reasons than the math and formulas.|
# 28 Sep, 2019 06:25
Drift Corrections…the update: So there was a break in the clouds last night which gave me the opportunity to put into practice the steps as written by Victor Land, many thanks Victor. Total time invested in working through this process ended up being 2 full hours before I was able to begin imaging, part of that span of time came from the fact that for some unknown reason my mount decided to not track the star I was focusing on despite my instructions…I soooo hate it when that happens! After a reboot of the mount all was in order again. My polar alignment and drift corrections still need a lot more practice and more factual understanding so, while I am still learning I thought I should write down some of what I "May" have discovered last night??|
1: Aligning the eyepiece cross hairs: I was aligning the cross hairs based on actual North/South/East/West directions as we see them on earth, not as they relate to movement directions of the mount i.e. East/West adjustments are made with the Azimuth knobs and North/South adjustments are made with the elevation knob.
2: Resist the temptation to make N/S and E/W adjustments on a single star, follow the instructions.
3: Don't be impatient, arguably my most difficult of challenges.
4: Recenter the target. I am still sorting this one out, not completely certain if I am doing this step properly but, after making an adjustment I am telling the mount to slew to the chosen alignment star again, the idea being that the star should be in the center of view assuming that the mount is tracking properly. This step has yet proven to be a correct procedure so, if you are reading this post…this step still needs to be proven.
As you can see, I am not even close to having this process and work flow completely sorted, this remains a work in process. After last night's exercise I was able to begin imaging however, I still noticed that with each and every frame captured, I still saw a lot of drift from image to image
# 28 Sep, 2019 13:59
Normally, doing this well enough for me to take unguided pictures of say 60 seconds (I am in a highly light-polluted area, so more without a filter doesn't make sense) at a focal length of 600mm, this takes half an hour or so. When I do use guiding, I know it helps because using the drift alignment tool on PhD2 shows I need to adjust still, but by rather small steps.
Just to comment:
1. When I say "align the crosshairs of your reticle eyepiece", I mean that when you have the star of choice in the center of the crosshairs and you push the direction buttons on your mount control, then the crosshairs are parallel to the movement the star seems to make in the eyepiece. I have a reticle eyepiece with double lines, so when I align the crosshairs and move the mount, the stars nicely stays in between the two lines both ways (so Up/Down and Left/Right).
So once you have done that, you center the star, let the mount track for 3-5 minutes (depending on your net focal length) and check again. You just need to see if the star moved up (which would be the same direction the star would move if you moved the telescope "down" or down (i.e. same direction when moving your telescope "up". Any motion left-right is just due to other errors and does not give any information about polar mis-alignment, so ignore it. FYI: pushing the"up" botton on e.g. a hand controller is not always the same as moving the telescope"up". That can usually be adjusted in the hand controller, so just check for yourself which way the star moves in the reticle eyepiece when you move the telescope up. I tend to do that mental check several times, otherwise you are adjusting azimuth in the opposite direction. Also, note that including a diagonal (or not) can change that direction due to the additional mirror.
2. This remark I do not quite understand. When you look at a star almost due south, you are looking to adjust the azimuth of the mount (so, you slightly move the mount-head east or west). When looking at another star close to the horizon, you are looking to adjust the altitude of the mount (so, you adjust the angle between the direction the mount-head is pointing and the horizon due north). This can not both be done from a single star, indeed. The whole deal is to have the rotation axis of the RA-motion of your mount pointing to the spot around which all the stars seem to rotate (due to the rotation of the Earth). This point is close to Polaris, but not quite at it.
3. I hear you!
4. I do this "by hand", i.e. just by using the direction (or slew) buttons and looking in the properly aligned finder scope first to get the star roughly centered and then finally making precise adjustments to center the star in the reticle eyepiece. This is why having a properly aligned finder scope is really important. Once you change your azimuth or altitude of the mount, the star will definitely move out of the FOV of your reticle eyepiece. Having to find it again "in the blind" (without a properly aligned finder scope) is terrible. So; step one of any observation session (right after balancing your scope) is aligning your finder scope with your OTA.
Now, I'm at 52 degrees north, so it is easier for me, because my mount has no problems with this altitude, but the principle behind drift alignment remains exactly the same.
Practice this a few times and once you have it down, having polar mis-alignment in the order of 5 arc-minutes and less is definitely possible and that within 20-30 minutes.
Again, I recommend doing it with at least 1000mm focal length. My imaging scope is a 600mm refractor, so I add a 2X barlow in front of the reticle eyepiece for a net focal length of 1200mm. When I use my Maksutov, it is 1800mm, which is fine. Doubling that to 3600mm is too much. The image just becomes way to dim to use your average star.
Hope this helps!
# 30 Sep, 2019 05:36
This is a video of how to do it. Andy also sells some software - StarTarg that is very good too.
I suggest using a barlow and liveview camera. It makes the process quicker as drift is magnified.
# 30 Sep, 2019 06:30
glennb44Glenn, this is a really helpful and nicely done video, thank you for sharing!
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