Polar alignment
- Piet Le Roux
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Polar alignment
I have a fork mounted 8" Meade LX90ACF and although I am competent in setting it up as a azimuth goto mount I want to become competent in setting it up as a polar mount, using its wedge, because I want to do some AP . I live on the south side so no pole star to assist me. The way I see it : 2 points that you have to get 100% is true South and your latitude angle which basically means your polar home position has to be near perfect. The next step is to check it and it appears that the only way to do that is with a drift test, remember I am in the south, so I have to learn to do that for the southern hemisphere. After I have accomplished this I must learn to do PEC training. I would like to hear from the accomplished AP guys as to how they would go about setting up at a unfamiliar star party site. I was thinking about placing a marker about 100m away exactly south to help me and placing cement blocks under my tripod legs to mark them and keep the legs stable. Any recommendations would be welcome.
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Re: Polar alignment
Hi Piet,
My method relies on using a bright green laser. This may not be appreciated at a star party although it the procedure only takes 4-5 mins and can be performed during late twilight beforeAP or serious dark sky observing begins. You also need a small pair of handheld binoculars - 25-35mm diameter. Most important thing is that they are small and light enough to be easily hand held in one hand while you adjust the laser in the other. It also relies on having a polar finder. You may be able to fit a polar finder to one of the fork arms. The finder can be very small because you only need to be able to see a bright laser once the laser is pointed at the pole.
The laser is attached to a fixed part of the mount not too far from the polar axis to minimise parallax. I attach mine to the top of the south leg.
To find the pole stars in the small binoculars, I usually start at theSMC and 47 Tuc. Jump to beta Hyd then to three stars, then to the sigma Oct trapezium see diagrams below. These stars are circumpolar for me and will also be for you at Bloemfontein. After you do it a few times, you'll find it gets easier each time. before long you can do it in your sleep. There are two stars, mags 6.8 and 7.8 that are very close to the pole. They are faint but visible in 25-35mm binoculars and if you place the beam between them and offset a little as shown in the diagram, you will be within a couple of minutes of the pole.
Once the laser is pointed, to just have to point the polar finder to the laser. I usually lower the polar axis elevation down below the pole, sweep the mount across until I see the beam in the finder then elevate the axis to the point of the beam.
The only problem for you is that you need to fit a polar finder. Once fitted, spend one night doing an accurate drift alignment and once aligned, set and lock the polar finder in position. If the finder is to be removable, you need to have a positive exact locating connection like a three pin registration plate.
Over 40 years in astronomy, I have used many methods of polar alignment, drift aligning, magnetic correction applied to compass and clinometer. This is by far the quickest and easiest. If the engineering & machining required to fit a polar finder is beyond your skills, you may wish to look at the polar master or sharp star computer assisted. But this method is quicker and at least as accurate.
Cheers
joe
My method relies on using a bright green laser. This may not be appreciated at a star party although it the procedure only takes 4-5 mins and can be performed during late twilight before
The laser is attached to a fixed part of the mount not too far from the polar axis to minimise parallax. I attach mine to the top of the south leg.
To find the pole stars in the small binoculars, I usually start at the
Once the laser is pointed, to just have to point the polar finder to the laser. I usually lower the polar axis elevation down below the pole, sweep the mount across until I see the beam in the finder then elevate the axis to the point of the beam.
The only problem for you is that you need to fit a polar finder. Once fitted, spend one night doing an accurate drift alignment and once aligned, set and lock the polar finder in position. If the finder is to be removable, you need to have a positive exact locating connection like a three pin registration plate.
Over 40 years in astronomy, I have used many methods of polar alignment, drift aligning, magnetic correction applied to compass and clinometer. This is by far the quickest and easiest. If the engineering & machining required to fit a polar finder is beyond your skills, you may wish to look at the polar master or sharp star computer assisted. But this method is quicker and at least as accurate.
Cheers
joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
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- Piet Le Roux
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Re: Polar alignment
The use of green lasers is , at this stage, accepted at my club so no problems there. A local Chinese importer had a whole selection of these lasers and I bought a couple of them.
here is a photo of my wedge/tripod south facing side. My leg is facing North but I don't see a problem mounting a adjustable laser mount on the tripod. But a polar scope is not a option. What if I set the laser on the polar South, the scope in its home position and then use my East/West fine adjuster and my wedge angle adjustment to fine tune it while I look through the telescope with a illuminated Astrometric eyepiece? I have a right angle spotting scope that I can mount on the scope would that not work?
here is a photo of my wedge/tripod south facing side. My leg is facing North but I don't see a problem mounting a adjustable laser mount on the tripod. But a polar scope is not a option. What if I set the laser on the polar South, the scope in its home position and then use my East/West fine adjuster and my wedge angle adjustment to fine tune it while I look through the telescope with a illuminated Astrometric eyepiece? I have a right angle spotting scope that I can mount on the scope would that not work?
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Re: Polar alignment
You mentioned AP , but I'm not sure in what context. AP requires accurate polar alignment - the better it is the more round your stars - less streaking. The Polemaster has a set up routine for southern hemisphere folks. I'd suggest checking it out. It does, however, require (USB) power, which may not be available in the field. Also the Polemaster is made to fit inside a polar scope hole, which I don't think your mount has.
I use "water-proof" duct tape to mark where my tripod legs go on my asphalt driveway. I've begun to notice that the legs (which have a nub on the bottom) are beginning to make an indentation in the asphalt - so my accuracy in placing the mount on the tape is really good, I guess. I have to replace the tape ~ every 4 months or so, but it is red and glossy and shows up well using a red flashlight. Also the tape leaves a white residue when it is worn out which makes placing replacement tape easy to do.
Hope this helps!
I use "water-proof" duct tape to mark where my tripod legs go on my asphalt driveway. I've begun to notice that the legs (which have a nub on the bottom) are beginning to make an indentation in the asphalt - so my accuracy in placing the mount on the tape is really good, I guess. I have to replace the tape ~ every 4 months or so, but it is red and glossy and shows up well using a red flashlight. Also the tape leaves a white residue when it is worn out which makes placing replacement tape easy to do.
Hope this helps!
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- Piet Le Roux
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Re: Polar alignment
Thanks for the feedback guys. I think Joe's idea is going to work for me but I am going to mount the laser on the wedge plate, that is 90 degrees to polar south, not on the tripod base. The laser I am going to use is designed for a gun sight and has internal adjustment for x and y. It will be able to shine on the polar south when the scope is in polar home position. The tilt of the wedge is adjustable and so is the east/west fine adjuster. So I would set the tripod up do a ruff adjustment on polar with the laser then mount the scope check it again using the fine adjustments, lock the plate and wedge nuts. One of the problems with a fork mount on a wedge is to get the OTA perfectly 90 degrees with its base plate, checking the polar setup through the spotting scope or the scope itself at the end should solve that problem. It will, take some time to get the laser properly aligned but I think its doable.
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Re: Polar alignment
Here's another suggestion that requires a DSLR with an LCD display and a piece of clear tape with a pinhole through it.
The idea is to first find the scope'sRA axis on the LCD using an RA slew with the DSLR at 6400 ISO/30seconds, then marking it on the LCD display by putting the pinhole at the center of the circular RA traces. Then, adjust the Alt/Az controls of the wedge to align the pinhole with the SCP (that is actually easier than with the NCP because we don't have as many bright stars near the NCP ) taking 3 second pictures iteratively. We assume that you have identified a asterism near the SCP that will help you eyeball the SCP location - should not be too hard. It's not much different than what the electronic polar alignment gadgets do, just without a computer.
If you try this you will probably find that the hardest part is to get the center of the circular tracks of theRA slew within the LCD screen. This will take a bit of cursing and trying but I can be done and practice helps.
The idea is to first find the scope's
If you try this you will probably find that the hardest part is to get the center of the circular tracks of the
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Re: Polar alignment
I use SharpCap's Polar alignment routine.
https://www.sharpcap.co.uk/sharpcap/fea ... -alignment
Works North or South. You just need to get within ~5° of either pole and follow the on-screen instructions.
GCG
https://www.sharpcap.co.uk/sharpcap/fea ... -alignment
Works North or South. You just need to get within ~5° of either pole and follow the on-screen instructions.
GCG
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- Piet Le Roux
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Re: Polar alignment
Ok mounting the laser is not going to be a problem...The scope is in polar home and the laser has a clear view of the celestial pole.
hope the weather clears so I can start testing!
hope the weather clears so I can start testing!
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Re: Polar alignment
I had a look at my old equatorial mount and the polar scope is mounted at your latitude angle and when it faces the celestial pole your mount is aligned. The polar scope is independent of any Ra and Dec movement. I have mounted my laser in the same way. So if my laser is aligned with my mount and is pointing exactly at the celestial pole, and my OTA is also pointing to the celestial pole, I can begin my two star alignment and I should be good to go? So Joe my conclusion is if you replace your polar scope with a laser you don't need a polar scope ?
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Re: Polar alignment
Hi Piet,Piet Le Roux wrote: ↑Mon Dec 02, 2019 10:04 pm I had a look at my old equatorial mount and the polar scope is mounted at your latitude angle and when it faces the celestial pole your mount is aligned. The polar scope is independent of any Ra and Dec movement. I have mounted my laser in the same way. So if my laser is aligned with my mount and is pointing exactly at the celestial pole, and my OTA is also pointing to the celestial pole, I can begin my two star alignment and I should be good to go? So Joe my conclusion is if you replace your polar scope with a laser you don't need a polar scope ?
I am glad you seem to have solved your problem. The method you are using is different to mine but yes, if the laser moves in ALT AZ with the polar axis and is precisely aligned then no you don't need a polar scope.
In my method, it is essential that the laser be attached to a stationary part of the mount. The laser is trained on the pole and then the mount pointed at the bright laser spot on the sky. I did it this way because I already have a precisely aligned polar scope but because of the mount weight, it's difficult to scan the loaded mount around and work out where I am pointing. The laser gives me a beam and an end point that are easy to fine with the mount
It's great that your scope has polar home position. This is effectively a polar scope so you don't need a separate one as I suggested. My technique does not work if the laser moves as you adjust the polar axis direction.
By attaching the laser to the wedge, the artificial pole star moves with the mount. Does it only move in azimuth or in elevation as well? I cannot tell from your picture.
If the laser moves in ALT and AZ with the polar axis then this is a defacto polar scope.
1 set the scope to polar home position
2 adjust the laser to the centre of the field of the scope
3 use handheld binoculars in one hand or the telescope finder to find the pole stars.
4 Point the laser at the 7th mag pole star and fine tune through the main scope
This method relies on the scope being able to reproducibly and accurately point at the mounts polar axis position. You can check this by pointing the scope polar axis at a distant object(even a close one would be ok since there is zero parallax), put the mount into polar home and slew the
Joe
Amateur astronomer since 1978...................Web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, Stellarvue 102ED, Saxon ED80, WO M70 ED, Orion 102 Maksutov, ST80.
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Re: Polar alignment
The binoculars in hand while pointing a laser routine is something I am use to : My Dobson is a treat to use since I fitted a green laser on it but when looking for dim objects I first get it in view with binoculars and then get the laser in view.
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Re: Polar alignment
With all respect, I doubt if this will work Joe. Your step 2 is difficult to implement and depends on uncertain assumptions. First, can we assume that the mechanical fork axis is exactly perpendicular to its base? Secondly, if that is the case, can we assume that the optical axis is aligned with the fork's mechanical axis? Third, can you align the laser exactly to the center of the scope's FOV ? Each of these three requirements must be accurate to about 1'. I think everything combined with your method this can easily be off by a full degree, and it is a lot of unnecessary alignment work.
This is why I advocate methods that use anRA slew to determine where the RA axis is pointing relative to the Az axis, then adjust the Az axis using the AltAz controls so this point coincides with the SCP . By doing that, none of your assumptions are needed and any inaccuracies resulting from implementing these assumptions, are avoided. By locating the center of RA rotation on a digital camera then moving that point to the SCP with the AltAz controls, you can achieve 1' accuracy directly. The Polemaster, Sharpcap and the computer-less method that I proposed will all do that. The use of a camera makes all of the intermediate alignment steps that you require, obsolete, and makes it possible to do PA to within 1' quickly.
This is why I advocate methods that use an
... Henk. Telescopes: GSO 12" Astrograph, "Comet Hunter" MN152, ES ED127CF, ES ED80, WO Redcat51, Z12, AT6RC, Celestron Skymaster 20x80, Mounts and tripod: Losmandy G11S with OnStep, AVX, Tiltall, Cameras: ASI2600MC, ASI2600MM, ASI120 mini, Fuji X-a1, Canon XSi, T6, ELPH 100HS, DIY: OnStep controller, Pi4b/power rig, Afocal adapter, Foldable Dob base, Az/Alt Dob setting circles, Accessories: ZWO 36 mm filter wheel, TV Paracorr 2, Baader MPCC Mk III, ES FF, SSAG, QHY OAG-M, EAF electronic focuser, Plossls, Barlows, Telrad, Laser collimators (Seben LK1, Z12, Howie Glatter), Cheshire, 2 Orion RACIs 8x50, Software: KStars-Ekos, DSS, PHD2, Nebulosity, Photo Gallery, Gimp, CHDK, Computers:Pi4b, 2x running KStars/Ekos, Toshiba Satellite 17", Website:Henk's astro images
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Re: Polar alignment
I don't understand the point you trying to make: The fork mount is a polar mount and works like any other. The fork's rotation is yourSkyHiker wrote: ↑Tue Dec 03, 2019 10:56 am With all respect, I doubt if this will work Joe. Your step 2 is difficult to implement and depends on uncertain assumptions. First, can we assume that the mechanical fork axis is exactly perpendicular to its base? Secondly, if that is the case, can we assume that the optical axis is aligned with the fork's mechanical axis? Third, can you align the laser exactly to the center of the scope's FOV? Each of these three requirements must be accurate to about 1'. I think everything combined with your method this can easily be off by a full degree, and it is a lot of unnecessary alignment work.
This is why I advocate methods that use an RA slew to determine where the RA axis is pointing relative to the Az axis, then adjust the Az axis using the AltAz controls so this point coincides with the SCP. By doing that, none of your assumptions are needed and any inaccuracies resulting from implementing these assumptions, are avoided. By locating the center of RA rotation on a digital camera then moving that point to the SCP with the AltAz controls, you can achieve 1' accuracy directly. The Polemaster, Sharpcap and the computer-less method that I proposed will all do that. The use of a camera makes all of the intermediate alignment steps that you require, obsolete, and makes it possible to do PA to within 1' quickly.
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Re: Polar alignment
I don't understand the point you trying to make: The fork mount is a polar mount and works like any other. The fork's rotation is yourSkyHiker wrote: ↑Tue Dec 03, 2019 10:56 am With all respect, I doubt if this will work Joe. Your step 2 is difficult to implement and depends on uncertain assumptions. First, can we assume that the mechanical fork axis is exactly perpendicular to its base? Secondly, if that is the case, can we assume that the optical axis is aligned with the fork's mechanical axis? Third, can you align the laser exactly to the center of the scope's FOV? Each of these three requirements must be accurate to about 1'. I think everything combined with your method this can easily be off by a full degree, and it is a lot of unnecessary alignment work.
This is why I advocate methods that use an RA slew to determine where the RA axis is pointing relative to the Az axis, then adjust the Az axis using the AltAz controls so this point coincides with the SCP. By doing that, none of your assumptions are needed and any inaccuracies resulting from implementing these assumptions, are avoided. By locating the center of RA rotation on a digital camera then moving that point to the SCP with the AltAz controls, you can achieve 1' accuracy directly. The Polemaster, Sharpcap and the computer-less method that I proposed will all do that. The use of a camera makes all of the intermediate alignment steps that you require, obsolete, and makes it possible to do PA to within 1' quickly.
here is a conventional polar mount compared to a fork mount in polar configuration...
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Re: Polar alignment
To answer the confusion about the AltAz, when I refer to AltAz in your configuration I mean the wedge's AltAz adjustments.
Yes I understand exactly what you are doing and what Oz is doing. I just want to point out that IMHO you will never get about 1' or 2' accuracy, which is what is needed for good astrophotography. I suspect that yours will be 10' or more. This results inDEC corrections which are detrimental.
This is why I pointed out that there are better methods using a camera that will give you better alignment. Many have failed makingAP work with a wedge. But no pressure, do what you like and good luck.
Yes I understand exactly what you are doing and what Oz is doing. I just want to point out that IMHO you will never get about 1' or 2' accuracy, which is what is needed for good astrophotography. I suspect that yours will be 10' or more. This results in
This is why I pointed out that there are better methods using a camera that will give you better alignment. Many have failed making
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Re: Polar alignment
Hi Piet,
As another alternative, I recently adapted my ZWO planetary webcam to fit my Canon lenses. If you get a "V" or "D" bar for the top of yourOTA (they're relatively inexpensive) and the adapter (also relatively inexpensive) to affix this setup to that bar, you can then use either SharpCap Pro or PHD2 to do your static PA. It will require a computer (laptop, tablet, etc) and it will take more time than the laser, but you won't be burdened with installation error that may be inherent in your laser setup. Plus it could also be used to autoguide your scope when doing long exposure AP . In the attached image, I have it mounted directly on the saddle of my mount (for doing a static PA) but it would work equally well attached to the top of your OTA . Hope this helps.
Cheers,
JT
As another alternative, I recently adapted my ZWO planetary webcam to fit my Canon lenses. If you get a "V" or "D" bar for the top of your
JT
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6R, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100 ∞ AP Gear: ZWO EAF and mini EFW and the Optolong L-eXteme filter
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°
Searching the skies since 1966. "I never met a scope I didn't want to keep."
∞ AP Scopes: #1: TPO 6" f/9 RC #2: ES 102 f/7 APO #3: ES 80mm f/6 APO
∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
∞ Mounts: iOptron CEM70AG, SW EQ6R, Celestron AVX, SLT & GT (Alt-Az), Meade DS2000
∞ Cameras: #1: ZWO ASI294MC Pro #2: 662MC #3: 120MC, Canon T3i, Orion SSAG, WYZE Cam3
∞ Binos: 10X50,11X70,15X70, 25X100 ∞ AP Gear: ZWO EAF and mini EFW and the Optolong L-eXteme filter
∞ EPs: ES 2": 21mm 100° & 30mm 82° Pentax XW: 7, 10, 14, & 20mm 70°
Searching the skies since 1966. "I never met a scope I didn't want to keep."
- Piet Le Roux
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Re: Polar alignment
Thanks again for all the inputs. But at this stage I am not looking for perfection I just want to learn the basics. So lets keep to the KISS principle.
step one: I want to find a practical way to do polar alignment(in the southern hemisphere) that does not need a lot of gear and is a pain to do.
Step Two: I want to learn to test my polar alignment with the drift method for the southern hemisphere.
Step three: I want to learn to doPEC training.
Once I am competent doing the above I will attach a camera.
step one: I want to find a practical way to do polar alignment(in the southern hemisphere) that does not need a lot of gear and is a pain to do.
Step Two: I want to learn to test my polar alignment with the drift method for the southern hemisphere.
Step three: I want to learn to do
Once I am competent doing the above I will attach a camera.
Main Equipment : Tele Vue 27mm Panoptic, 7&13mm Nagler, Big Barlow : 8" Meade LX90ACF with Meade 2.0" Enhanced Diagonal : Camera Fuji XT100
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