Subterralien
member
Reged: 10/27/07
Posts: 56
Loc: Colorado
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So I've had this telescope and all my equipment to use it for nearly a YEAR now and I finally took it out last night (moved to a realistic location) and spent hours trying to polar align it and such. I got to the point where I had three calibration stars, and every thing I asked it to go to was in the center of the frame.
All the settings were correct (date/time/DST/etc), but my exposures would trail after 5 seconds or so. I know this mount isn't supposed to give you an hour of perfect tracking, but I know it has at least the potential to do 1 minute, if not a little less. My load is very small, just an Xti prime focused on the tube and that's it.
What could I be doing incorrectly? I have the tracking mode on sidereal/EQ-north.
I searched for other similar topics but they all differed in some way from mine. Thanks!
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-Alex
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22472
Loc: NE Ohio
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Polar alignment and star alignment are two different things. Three star alignmet will permit accurate goto operation despite a poor polar alignment - but tracking is dependent ONLY on polar alignment.
The quickest way to get a decent polar alignment if you don't have a polar alignment scope is to eyeball Polaris in the center of the hole where a PAS would be.
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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME
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btieman
super member
Reged: 07/24/08
Posts: 114
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You might try centering stars with a higher power eyepiece.
I have an alt-az scope (CPC1100) and I can image for over 1 minute unguided without trails or field rotation with a focal length of ~1000. At a fl of 2800 I can get 30 seconds--sometimes better.
I usually align on planet/moon early in the evening and then replace stars as the night goes on. Not sure how your scope works, but the CPC1100 lets you swap the current object for one previously used in the alignment calculations.
I did find my alignments and tracking got much better after I started using a 12mm illuminated retical to align with--much easier to get the star aligned to center with an illuminated retical!
A good polar alignment will let you align so as to not have field rotation, but A good 3 star alignment even in alt-az will allow imaging of a minute+ depending on focal length.
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CPC 1100
Meade DSI Pro
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DaemonGPF
Pooh-Bah
Reged: 03/22/08
Posts: 1480
Loc: New Mexico
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Did you star align again after polar aligning? It's still needed to properly map the sky. A recommendation I would make is to unfocus the stars when aligning to make them into big circles. It makes it much easier to determine if they are accurately centered, and of course, do this at higher power as recommended above.
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-Josh
*Orion Starblast Imaging 150mm OTA
*Orion Starblast Imaging 114mm OTA
*Meade 50mm AR short tube OTA
*Meade DSI Pro IIc
*Orion Starshoot DSCI
*CG5 mount
http://cleardarksky.com/c/AlbuqNMkey.html
My Messier Project Gallery
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22472
Loc: NE Ohio
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Quote:
You might try centering stars with a higher power eyepiece.
That'll make a difference in tracking with an alt/az mount, but on an EQ mount the star alignment doesn't have any effect on tracking. In fact, with an EQ mount it isn't necessary to do a star alignment at all for tracking; it's necessary only if goto operation is desired.
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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME
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bebert
member
Reged: 07/21/08
Posts: 52
Loc: Arklatex
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I use the same mount. If I'm not going to do any serious imaging, I usually do the following:
1) Rough align Polaris by centering it through the hole where the polar scope would be. Just eyeball it.
2) Perform the standard 2-star alignment. I don't bother with calibration stars at this point.
3) Perform a 'polar align' using the hand controller. This wipes out your previous alignment.
4) Re-do the two star align.
You can also repeat steps 3 and 4 to increase accuracy. Once you're satisfied, your final step 4 should include calibration stars.
I use a 9mm reticled eyepiece to get everything as exact as I'm able. I've found that a few iterations of this along with autoguiding is usually good enough for my purposes. Drift alignment would be best, though.
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Celestron C8
CG5-ASGT
Orion Starshoot autoguider
Vixen 70s for guiding
PHD Guiding
Canon 300D unmodified
0.63 focal reducer
10:1 Crayford
Bahtinov mask
various cables, filters, EPs
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EWhytsell
super member
Reged: 06/15/08
Posts: 166
Loc: North Central Ohio
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Just for the sake of keeping it simple, did you remember to set the tracking to on and the guide rate to sidereal? 5 sec is way to short of a time for star trails.
Evan
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Classic C8 Super Polaris upgraded to CG-5 mount
Canon 40D unmodded
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scully1234
super member
Reged: 09/04/07
Posts: 146
Loc: Rush, NY
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Yes Evan is on the right track.
I use this mount heavily.
Verify that you have tracking MODE set to EQ North and the RATE set for SIDEREAL.
Star trails after 5 secs usually means tracking MODE is OFF.
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Astrophotographer wannabee !
Woot ! check out new cam in the equip list !
Celestron C8 XLT on the CG-5 mount
Meade 70mm AZ guide scope
Canon EOS 450D (xsi)
DSI color
Canon A530 point-n-shoot
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Buhlig
member
Reged: 12/03/07
Posts: 60
Loc: Derby, KS
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The comment about polar alignment and star alignment being totally different is dead on. You could have a terrible polar alignment and goto will function. Trails after 5secs would point to a heinously wrong physical declination setting of your mount, because the CG-5 does not track in Declination Is it set appropriate for your latitude? By the way, eyeballing and/or the polar scope aren't really good enough for useful astrophotography of dim objects....and the CG-5 is balky in autoguide mode with large PA errors.
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Celestron 80mm ED Apochromatic Refractor
Orion 8" Newt
Celestron 80ST achro (guider)
PHD via handcontroller interface
CG-5 Advanced GT Mount
Canon 350D
Philips SPC900NC
http://www.flickr.com/photos/derbysluggers/sets/72157605255114566/
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bebert
member
Reged: 07/21/08
Posts: 52
Loc: Arklatex
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Honestly I haven't experienced problems with that method when it's used appropriately. Its appeal is speed not accuracy. Sure, a drift alignment is best for imaging but I was giving him a procedure to run through so as to eliminate possible sources of gross error (he didn't specify exactly how he attempted to align the mount). I know I can track for longer than 5 seconds using that method without guiding.
Alex - you might also check to see if you've got the latest firmware for the motors and controller.
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Celestron C8
CG5-ASGT
Orion Starshoot autoguider
Vixen 70s for guiding
PHD Guiding
Canon 300D unmodified
0.63 focal reducer
10:1 Crayford
Bahtinov mask
various cables, filters, EPs
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Subterralien
member
Reged: 10/27/07
Posts: 56
Loc: Colorado
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Thank you for all the responses! Most of what has been mentioned I've got down correctly - but I think what may be a problem is the fact that my Index markings are inaccurate - by an inch or so?
Is that common? Or are index markings always dead on for the scope out of the factory?
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-Alex
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jrcrilly
Refractor wienie again
Reged: 04/30/03
Posts: 22472
Loc: NE Ohio
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Quote:
I think what may be a problem is the fact that my Index markings are inaccurate - by an inch or so?
They aren't intended to relate to anything in particular (they merely designate a starting position) so I'm not sure what you mean by "inaccurate". What's important is to always use them, as a consistent starting position helps reduce alignment time by keeping the error to the first alignment star to a minimum. If the topic is still tracking performance, then it's worth knowing that they aren't involved with tracking in any way.
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John C
Urban Observatory
Tele Vue Pronto
A&M/Astreya 76mm F/6 APO
TMB/LOMO 80mm F/7.5 APO
Tak FSQ-106N F/5 APO
Meade 152ED F/9 "APO"
152mm F/10 achromat
Tak CN-212 8" F/12 classical Cass/ F/4 Newt
Teeter 20" F/3.8 truss Newt w/ServoCat
LXD750, EM-200, CI-700
ST-10XME
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Subterralien
member
Reged: 10/27/07
Posts: 56
Loc: Colorado
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Haha that actually resolves so much for me. Thanks, had my steps out of order.
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-Alex
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Subterralien
member
Reged: 10/27/07
Posts: 56
Loc: Colorado
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Thanks for all the help!
My hand controller (c80ed w/cg-5asgt purchased from astronomics in winter 2008) doesn't even have a three star align on it, just two star with calibration stars. I assume that's the same thing.
My current setup procedure so far is this: I
1) On the mount: set latitude, aim at north w/ compass
2) Set time/date on the RA circles
3) Make the mount level
4) look through polar hole and try to place polaris in the center via slight alt/azi adjustments
5) Run a two star align
6) Select polar align under utilities (usually is already pretty accurate) and correct with alt/azi
7) two star w/2 or 3 calib stars (now I know this has nothing to do with polar alignment)
Should I repeat 6 and 7? Does that actually improve the accuracy? I am without an illuminated reticle at this point and may not have one in the near future, so I'm assuming this is the best I can do until I get one. I'm averaging the beginnings of trails on 14~ second exposures with my 80mm. With a big "meh" I present to you, terribly polar aligned m13.
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-Alex
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DaemonGPF
Pooh-Bah
Reged: 03/22/08
Posts: 1480
Loc: New Mexico
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Quote:
Quote:
You might try centering stars with a higher power eyepiece.
That'll make a difference in tracking with an alt/az mount, but on an EQ mount the star alignment doesn't have any effect on tracking. In fact, with an EQ mount it isn't necessary to do a star alignment at all for tracking; it's necessary only if goto operation is desired.
True. I suppose I should stop and read the question a little more thoroughly before responding. For some reason I had Go-To stuck in my head.
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-Josh
*Orion Starblast Imaging 150mm OTA
*Orion Starblast Imaging 114mm OTA
*Meade 50mm AR short tube OTA
*Meade DSI Pro IIc
*Orion Starshoot DSCI
*CG5 mount
http://cleardarksky.com/c/AlbuqNMkey.html
My Messier Project Gallery
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DaemonGPF
Pooh-Bah
Reged: 03/22/08
Posts: 1480
Loc: New Mexico
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Quote:
Thanks for all the help!
My hand controller (c80ed w/cg-5asgt purchased from astronomics in winter 2008) doesn't even have a three star align on it, just two star with calibration stars. I assume that's the same thing.
My current setup procedure so far is this: I
1) On the mount: set latitude, aim at north w/ compass
2) Set time/date on the RA circles
3) Make the mount level
4) look through polar hole and try to place polaris in the center via slight alt/azi adjustments
5) Run a two star align
6) Select polar align under utilities (usually is already pretty accurate) and correct with alt/azi
7) two star w/2 or 3 calib stars (now I know this has nothing to do with polar alignment)
Should I repeat 6 and 7? Does that actually improve the accuracy? I am without an illuminated reticle at this point and may not have one in the near future, so I'm assuming this is the best I can do until I get one. I'm averaging the beginnings of trails on 14~ second exposures with my 80mm. With a big "meh" I present to you, terribly polar aligned m13.
If you want to save a significant amount of time (some may disagree but this works just fine for me so I'd say it's valid) instead of going through step 5 as a "two star alignment" just select "last alignment" or "quick align" and when it says ok, go forward with step 6 and 7. If you're generally pointed to polaris from the get go, then the two star align before the polar align is not necessary, just do it after.
--------------------
-Josh
*Orion Starblast Imaging 150mm OTA
*Orion Starblast Imaging 114mm OTA
*Meade 50mm AR short tube OTA
*Meade DSI Pro IIc
*Orion Starshoot DSCI
*CG5 mount
http://cleardarksky.com/c/AlbuqNMkey.html
My Messier Project Gallery
|
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