Trying to polar align a Meade LXD75

[Deimos]

Hi all,

Having been an amateur terrestrial photographer for a while now I recently caught the astronomy bug and purchased a DSE 114mm Newtonian Reflector just to try (on special for $148, so who could complain). Whilst the OTA optical quality seems OK, the EQ mount it comes with certainly isn't. Tightening the tripod leg bolts beyond what I would consider normal removed a lot of the basic wobble, but there's a lot of play in the RA/Dec axes as well. Trying even lunar photography with a Konica Minolta Z5 looking down the eyepiece was a let down. Setting the 10 second timer and pressing the shutter button, the scope was still shaking significantly when it went off - a sign of really poor damping. (This was a clam windless night, too.) And no option of remote shutter release on the KM. :(

So I went out looking for better quality EQ mounts, with goto, but on a budget. I had a tough choice between a Celstron Advanced Series GT and the Meade LXD75 with an Autostar 497 controller. Both units were virtually the same price and both looked mechanically sound - each dealer decried the other's hardware as insubstantial, but they looked and felt the same to me. I finally chose the Meade because I knew for certain that I could get software to work with it (using ASCOM drivers or directly with LX200 protocol) and it came with a polar alignment scope built-in whereas the ASGT only had provision for one.

Now comes the fun. ;)

Certainly a huge improvement on stability. I'm finally getting some half-decent shots (of bright objects, anyways, the KM doesn't have good low-light capability and a maximum 4-second shutter speed).

But the goto capability leaves a bit to be desired. I've tried using "easy", "two star" and "three star" aligns. Whilst it gets bang-on-the-money when you ask for one of the stars you aligned with, it's often 3-4 degrees out on other objects (according to the Telrad). I couldn't make it find M7 the other night no matter how hard I tried.

I'm told it's all due to polar alignment, especially since I've glued N-S and E-W bubbles on the tripod base to ensure it's level. The latitude scale is essentially unusable (why must the indicator arrow be so far away from the scale I wonder?) but I've set it fairly closely to my latitude using a bubble level on an adjustable square. Being within 10km of the city lights, though, I'm having real trouble finding Chi- Sig- Tau- and Ups-Octantis to make real use of the polar align scope and its etched overlays.

Can anyone provide me with suggestions for southern polar aligning the Meade, or even other methods of alignment? Most of the material out there spends reams on finding NCP using Polaris, but barely a line or two on finding SCP with Octantis.

[Next task: fighting-off the aperture bug - I'm eyeing-off a Guan Sheng GS-980 12" Dobs.]

[[1ponders]]

Hi Deimos. Welcome to the forum.

There are a number of ways to polar align your scope. Do you actually use the polar alignment scope to find the SCP? I've known a few people who have had LX75s and have found the polar alignment scope next to useless unless you actually know how to use it :P Bit of an ask for someone who is new to the mount. Also have you trained the drives?

The Autostar should take care of most inaccuracies when you do your alignment, but of course the further out from the pole you are the less accurate it is going to be. The best suggestion I can give you is to learn to drift align. It isn't difficult to learn and you will need to be able to do it for imaging anyway. There is a great simulator available. Check out this post with the simulator link (http://www.iceinspace.com.au/forum/showthread.php?t=13272)

Once you have drift aligned a few times you get a good feel for where south is anyway. Btw for visual work you don't need to be accurate to the arcsec, an alignement procedure of 15 min will probably get you accurate enough for the autostar and visual work.

Alternatively to the simulator you can join us tomorrow week at Astroron's for our monthly Cambroon (near Kenilworth) get together. There is a map at the top of the Star Party and Observing Session forum. Check the events calendar for when it's on. You would be more than welcome and staying overnight is not a problem. Pm me if you'd like more details.

[Deimos]

Thank you. Hopefully I'll be able to contribute something useful in the near future.


I've tried using the polar scope, yes, but it's seems a very narrow FOV and to make things "interesting" is flipped both vertically and horizontally. The Meade manual speaks very little to its use in the southern hemispere.

One thing I thought of trying this afternoon (although I didn't get home in daylight to try it) was to point the polar scope at a distant object (like top of a Mt Coot-tha TV tower), align the OTA to the same point and draw reference marks on the RA/Dec axes. Then when I go to setup at the field I could lock-off the RA/Dec axes at those marks and then rotate the tripod/latitude adjustments until the stars I need are in the right place in the main scope. I should then be able to finish it off using the polar scope. Getting and keeping visual contact of the Octantis stars seems to be the hardest part for me, though.


The agent I bought it from did this in-store, but I'm going to do it again.


I'll try that out as well.


Thanks for your help and the invite. I'll be heading up to Mount Kent Observatory (http://maps.google.com/maps?f=q&hl=en&q=-27%C2%B0+47%27+52.00%22,+%2B151%C2% B0+51%27+19.00%22+%28Mount+Kent+Obs ervatory%29&z=16&t=h) about 30km SSW of Toowoomba for the AAQ field night next Saturday (23-Sep).

[[1ponders]]

There will definately be someone up there who can show you how to drift align. It's as important to eq users as being able to collimate is to newt users.

[Fox]

G'day Deimos. I got my LXD75 earlier this year. I have found the mount to work very well for me. I must admit that I don't know how to polar align using the drift method, but in my opinion, the LXD polar alignment scope is spot on for me. The LXD recticle 4-sided pattern of Octantis is not flipped/reversed as you state, the pattern is as according to charts and how you see it through binoculars.

When I first set up the mount, I initially located the pattern of Octantis using binoculars. Then, if you have the LXD tripod pretty level, it should be relatively easy to locate Octantis through the polar scope, adjusting the latitude angle with the two screw adjusters, and adjusting the horizontal azimuth control screws. I ignore the 24hour clock/date/meridian indicator dial on the mount, and just rotate the mount in RA until the orientation of Octantis in the reticle matches what's showing in the sky. Once this is done, next time you set the mount up, all you need to do is make sure the level is good, and only the azimuth should need adjustment to find Octantis again (since the latitude should be set for that location).

The more often you do this, the easier it becomes; it takes me less then 5 mins to align well now. Thereafter, the Goto is magic, locating most objects within 0.5 deg or so.

[Dennis]

Hi Deimos

I have successfully used the Polar Alignment Scopes (PAS) in my Vixen GPDX and Tak EM200 mounts in Brisbane and can sympathise with you as a new comer to aligning using the PAS.

The 4 trapezium pattern stars are quite dim in the light polluted skies of Brissie, but once found are very easy to see. I have driven markers into the back garden for my pier and tripod legs so when I set up, I plop the legs onto the markers and then touching up the polar alignment only takes a matter of 30 seconds.

I live in S Brisbane and would be happy to show you how I polar align with my set up – just PM me. You should then be able to translate the technique to your system and I'm sure it will become much easier then.

Cheers

Dennis

[Davo3960]

Deimos, also owning the LXD75 I know where you are coming from. I struggled to use the polar scope and found very little info about how to use it. I still dont know how to. There are heaps of tutorials around explaining how to drift align so I learnt that. Once I drift aligned I marked the mount on my verhanda and can now just plonk it back in the same spot. Even just aligning the scope to south with a compass (and having the latitude set correct and mount level) and then doing a 2 star alignment, the autostar always puts what I select in the FOV of the 26mm eyepeice.

[Deimos]

Hi Fox,


You and I must have different versions of the LXD75 Polar Alignment Scope. I just took mine outside and verified against landmarks that the view is indeed both left-right reversed and up-down reversed.

The Octantis star closest to the egde of the view (which I'm assuming to be Chi Octantis, see attached pic) is so close to the edge of the view that it doesn't get lit by the reticle illuminator unless I turn it up to full brightness, at which time you can't see the starfield any more because it gets overwhelmed by the red light. Still, if I could get the other three stars in the marks that should be OK.

1ponders suggested the Astrophotography Guiding Simulator (http://www.petesastrophotography.com/tutorial/guidingsim.html) above, which teaches you how to drift align. I've had a play with this and think I can make it work in the field - unfortunately it has been overcast the last couple of nights so I haven't been able to.

PS: This is the first time I've tried to attach a pic. I apologize if I've done it incorrectly.


http://www.arich.webcentral.com.au/astronomy/Octantis.png

[Deimos]

Hi Dennis,

I'm living in units at Morningside and don't have very much of the sky available, even when in the back "yard".

When observing I tend to go a little further out of town to my aero club at Minnipi Parklands (beside the Gateway), which is mostly surrounded by trees and so not getting overwhelmed by street lamps in the eye. I could try plonking some alignment pegs down, I suppose, but might get a few scowls from my fellow club members. ;)

[Deimos]

Hi Davo,

Yes, drift aligning would seem to be the way to go. Snippets I've seen discussing polar alignment scopes and drift aligning seem to suggest that the latter is only a precursor to the former, and that drift aligning is essential anyway if you're going to do long-exposure atrophotography.

Thanks,
Deimos.

[Fox]

G'day Deimos. The shape/pattern of Octantis I have in my LXD75 PAS looks exactly like the picture you attached in your post, which is also identical to Norton's and Wil Tirion atlases, and the same as shown on page 52 of the Meade LXD75-series manual. The Star closest to the perimeter in my PAS is Upsilon Octantis - which is entirely consistent with the location of the South Celestial Pole and true orientation of Octans. If indeed Chi Octans is closest to the perimeter through the view in your PAS - then something is truely amiss with your PAS!

The only way I could see your PAS view being flipped/reversed/inverted would be if the manufacturers made some wrong patterns at one stage and you ended up with a dud one, or during assembly the recticle was inserted back to front (?). If the latter was true, do the 40' and 60' numbers to align Polaris look reversed as well? Your situation really sounds odd.

In any case, I reiterate the same as others have posted, after you have a few goes at successful polar alignment, it becomes much easier thereon. I agree with Davo3950, after good alignment, objects are placed within my 26mm Plossl >95% of the time, it's real magic.

Some 15 years ago, I got a "Kenko Beta-plasma-Ex" mount, essentially a SuperPolaris GEM clone - it was $1,450 back then. Now, for the same money, and not even taking into account inflation/CPI, you get a much better mount with full-on computerised Goto, I reckon that's amazing! The LXD has some drawbacks, granted its not in the same league as Losmandy, Sphinx etc., the tripod is a bit crude, much of the metal is obviously el-cheapo recycled pot aluminium, the gears in mine have significant loosness and backlash so I am really looking forward to doing the strip/polish/regrease Hypertune thing anyday now (the Hypertune DVD is fantastic). Overall I think it's great value for money given I am only mounting a Genesis, and I did not want to spend $3,000 for that next level of mount. Cheers, Fox.
:)

[Deimos]

Hey Fox,

Well yes the reticle patterns, including the 40/60' numbers for Polaris alignment against NCP, are readable and the Octantis trapezoid appears to be the correct way around based on the diagram I submitted. I'm leaning towards a barf of the optics at the factory, because the visuals through the PAS are most definitely flipped and mirrored.

I did find that the GOTO functionality was much improved the other night when I tried to do a drift alignment. I don't have a crosshair/grid reticle eyepiece for the OTA, so I was trying to do this with the OTA's finderscope which does. (Something else on the acquisition list, I guess - has anybody tried the 12.5mm Illuminated Reticle Eyepiece (http://www.myastroshop.com.au/products/details.asp?id=MAS-219) from MyAstroShop?)

I'm thinking the real secret to cracking GOTO accuracy is to not just align the alt/az (latitude/azimuth) adjustments to point at the SCP (and have the OTA returned to the Dec "home position"), but to also get the RA axis perfectly oriented so that its rotation matches the position of Octantis around SCP. At the moment all I've been able to do is return the RA axis back to the "home position" marked by the two triangles.

It's looking fairly clear tonight, so I'm going to try heading down to the field again and have another go tonight.

Thanks for your suggestions, guys.

Deimos.

[Fox]

Sorry Deimos, I am obviously still not quite following you here (no offence! it's sometimes hard not being able to see a problem 1st hand, and only having text to go by). If, as you say, your Octantis recticle trapezoid is the correct way around as based on the submitted diagram (the pattern in my LXD75 PAS exactly matches your diagram too) - then to me, this must mean that your PAS recticle is a really OK (?). By then saying the visuals through your PAS are flipped and mirrored - isn't this contradicting your previous statement? Or am I still missing something here.

We are assuming your PAS is reasoanbly well aligned within your RA axis, this can be a problem from what I have read. Apparently there are 3 set screws you can play with, you can adjust the PAS alignment during the daytime by adjusting these set screws whilst focusing on a static distant landmark and 'rotating the RA axis' method. Apparently it can be quite a chore though since using three screws makes it fussy to adjust, and the screws are small and somewhat embedded I believe.

Good luck...! Cheers, Fox

[Deimos]

Hey Fox,

No offence taken. I'm new to this field and am probably not explaining myself using the correct terminology.

The text and patterns of the illuminated reticle inside the PAS appear to be in their correct orientations, based on the diagram on page 52 of the Meade LXD75 series manual (http://www.meade.com/manuals/TelescopeManuals/LXDseries/LXD-75C.pdf) (935k PDF warning) and the Octantis pattern I attached to my earlier message.

I'll try to explain the problem with the visuals when looking at things through the PAS.

The view through the PAS, as opposed to what's seen on the reticle inside it, is left-right mirrored and flipped top-bottom as well. This is confirmed by looking at terrestrial objects - trees are hanging down from the sky and signs read right-to-left as if in a mirror.

If I rotate the azimuth to the right I would expect the star field viewed through the PAS to scroll to the left as the FOV pans to the right across the heavens, but instead the star field scrolls to the right. Likewise, if I lower the altitude (latitude) I would expect the star field viewed through the PAS to scroll up as the FOV drops down through the heavens, but instead the star field scrolls up.

So it's not just near-field (terrestrial) objects that are flipped and mirrored.

The problem with this is that it makes lining-up Octantis on the reticle impossible - the Ups-Chi side of the reticle pattern is towards the top of the reticle, whereas the Ups-Chi side of Octantis as viewed through the PAS is towards the bottom of the reticle (even though it's on the top or closest to Octans proper in the sky). If I rotate the RA axis through 180 degrees to at least make the Ups-Chi side of the reticle and star field versions line-up then the the opposite side (Sig-Tau) won't match because its two stars are swapped out of position (note: this means Ups-Chi are swapped around as well).

Hope this makes it clearer.

On a brighter note, I did go through about six alignment sessions with the mount tonight before the clouds rolled in. Using Achemar and Formalhaut for two-star alignments I eventually got down to results of 37'^ 0'<. I could goto Alpha Cent. and Hadar fairly accurately and was still within 4 degrees of Aries (just) when swinging around to the other side of the sky.

I'll contact the Meade agent tomorrow to see if he thinks the PAS is OK.

[Deimos]

Dang typos: "I would expect the star field viewed through the PAS to scroll up as the FOV drops down through the heavens, but instead the star field scrolls up." should read: "I would expect the star field viewed through the PAS to scroll up as the FOV drops down through the heavens, but instead the star field scrolls down."

[Fox]

Ahhh...! yes, it was me all along, now I see exactly what you are getting at. And to make you happy (and me unhappy) I agree with your observation and summation; I just checked out my LXD PAS on an indoor object and indeed the optical image is upside down and mirror reversed! I could have sworn that I seem to be able to match the trapezoid of Octantis when I use it to polar align - I obviously have been so 'uncritical' of matching up the asymmetrical trapezoid whilst I am polar aligning - I haven't even noticed they don't quite align!

Its cloudy here at present, but I'll tell you what I find after my next outing. Keep us informed of your meeting with the 'Agents of Meade' - is it a design flaw or what? Thanks for the reality check.. Fox!

[Fox]

BTW, Davo3960, have you ever noticed Deimos's issue about the LXD75 'sky view' through the PAS being inverted/reversed - such that the recticle pattern of Octantis cannot be aligned? Fox

[Dennis]

Hi Guys

The straight through view of a refractor (finder, PAS) is always upside down and backwards unless we insert an erect-image diagonal?

Check your PAS against the scanned image from the Vixen GPDX manual below. Are they the same orientation? If so, you should be ok.

Cheers

Dennis

[Fox]

Thanks Dennis, yeah the LXD75 PAS recticle pattern matches your info, and I've always been under the impression all is well in actual practice. I am a tad confused, so I will take careful look next observing session.

[Davo3960]

That might be why I found it difficult to use, Fox. I'll give it another try using the above info and see how go. Polar aligning would certainly save some time if I take my scope to another site.

[Fox]

Hi Davo3960 and Deimos

Solved the apparent 'PAS issue'. I went out tonight and was able to match the LXD PAS recticle pattern exactly to the sky view pattern of Octantis, and thus obtain precise polar alignment.

I should have thought of this earlier, the explanation is basic lens optics '101'. The PAS polar scope will turn (ie. rotate) the view upside down (as typical lenses do), but it does NOT mirror invert it left to right. This is why the recticle pattern of Octantis is still valid to relate to any star map/atlas (as Dennis shows above). Because of this, although the sky view of Octantis through the PAS will look upside down (compared to say the naked eye or binoculars) you still align to this pattern via rotation of the PAS around the RA axis.

Try this for yourself, draw a diagram of Octantis on a sheet of paper, and say write a word as well in large capitals (using thick texta will help), and stick it on the wall about 10 feet away. Now look at your diagram and word through the PAS, you will see it is only rotated 180 deg upside down, but not mirror inverted (the image will 'appear' to be backwards, but it is not truely mirror-inverted, only backwards because it has been rotated 180 deg!).

So all up, the PAS is 100% accurate. A tip for finding Octantis using the PAS, find the pattern via 7x50 binoculars first, then you will know how to pre-rotate the PAS first and how it will look when you try searching for it through the PAS - this will help greatly because the pattern is faint if light pollution is a bug bear.

47 Tucana was glorious tonight through the Genesis and 6mm Radian...!

Cheers
Fox