fuadramsey
member
Reged: 06/26/07
Posts: 49
Loc: Orange County, CA
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How much exposure time should I be able to pull from a good EQ mount polar alignmend and/or drift aligned non-guided?
So far I can get a pretty solid 90 seconds on my mount. I tried drift algining last time and did not notice an increase in tracking. Maybe my polar alignment is pretty good, or I am not doing the drift alignment that good. Or maybe that is all I can expect without guiding?
Please advise.
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jay52
Carpal Tunnel
Reged: 09/26/04
Posts: 2280
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I can do 10 to 15 minutes at 2857mm focal length unguided with my Paramount ME.
So, I wonder what your definition is of "good EQ mount"?
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jay
www.allaboutastro.com
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fuadramsey
member
Reged: 06/26/07
Posts: 49
Loc: Orange County, CA
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Good one!
Maybe I should have said "basic mount" $400-$2,000 range.
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Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 1850
Loc: Piedmont, California, U.S.
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As you can tell from Jay's response, the answer is... It depends.
How good is the mount? How long is the focal length of the telescope? How good is the polar alignment?
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- Jared Willson
- Fluorostar FLT-110 w/ TEC optics
- Vixen VC200L
- Astro-Physics Mach1 GTO
- Stellarvue SV80S
- Takahashi Teegul SP Mount
- STL-11000
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Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 1850
Loc: Piedmont, California, U.S.
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Quote:
Good one!
Maybe I should have said "basic mount" $400-$2,000 range.
With my old Celestron AS-GT and an 80mm f/4.8 refractor (385mm focal length) I could get sixty second exposures after a basic 3 minute drift alignment. With my old Losmandy GM-8 and 715mm focal length refractor I couldn't go more than forty seconds or so before I was throwing out too many subs. Better mount, but the extra focal length and weight made the task more difficult. I believe these numbers are somewhat below average based on other people's postings.
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- Jared Willson
- Fluorostar FLT-110 w/ TEC optics
- Vixen VC200L
- Astro-Physics Mach1 GTO
- Stellarvue SV80S
- Takahashi Teegul SP Mount
- STL-11000
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Nils_Lars
scholastic sledgehammer
Reged: 01/04/08
Posts: 903
Loc: Santa Cruz Mountains , CA
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I got 2 min on my AS-GT unguided on the 6" SCT by running the polar align routine.
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Erik
Orion ED 80
Orion Atlas GOTO mount
Williams Optics reducer
Various eyepieces and other gear
Baytronix 80mm guidescope
Orion Starshoot Autoguider
PHD guide
Canon 400D (unmodded)
Stilleto Focuser
Tamron 75-300mm&28-80mm lenses
NexImage webcam
http://home.comcast.net/~eriknlarsen/site/?/photos/
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fuadramsey
member
Reged: 06/26/07
Posts: 49
Loc: Orange County, CA
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I was looking for a general answer. -Yes I know there is no general answer, but I wanted to get a feel of what others are getting out of a mount in the "basic" range $400-$1,000.
MY focal length is 750mm on a Celestron CG-4 Polar aligned with a polar scope. I was trying to determine if drift alignment will improve my tracking. Like I mentioned after my first try with drift aligning, I did not notice any increase in tracking.
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Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 1850
Loc: Piedmont, California, U.S.
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Quote:
I was looking for a general answer. -Yes I know there is no general answer, but I wanted to get a feel of what others are getting out of a mount in the "basic" range $400-$1,000.
MY focal length is 750mm on a Celestron CG-4 Polar aligned with a polar scope. I was trying to determine if drift alignment will improve my tracking. Like I mentioned after my first try with drift aligning, I did not notice any increase in tracking.
Better polar alignment always improves the tracking, but you will get diminishing returns. At some point periodic error will be much larger than declination drift, and further improvements in polar alignment will bring very few benefits. If you are already at 90s with a CG4 and 750mm focal length I would quit there. That's already much better than I was ever able to get out of my Losmandy GM-8. unguided with a similar focal length.
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- Jared Willson
- Fluorostar FLT-110 w/ TEC optics
- Vixen VC200L
- Astro-Physics Mach1 GTO
- Stellarvue SV80S
- Takahashi Teegul SP Mount
- STL-11000
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sang33ta
professor emeritus
Reged: 07/08/08
Posts: 539
Loc: UK
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Drift alignment is an alternative to polar alignment. If you have polar scope and can see polaris stick with that. If you want more use the autoguider port.
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Hioptic 152mm f12.5 Maksutov
Celestron Advanced CG5-GT Mount (Mr Noisy!)
Meade 4000 Super Plossl Set
Casio QV-2900UX
Got fed up of waiting for Meade ETX-150 so put this together for £500/$1000 
Edited by sang33ta (08/21/08 06:20 PM)
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Jared
Carpal Tunnel
Reged: 10/11/05
Posts: 1850
Loc: Piedmont, California, U.S.
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The catch is that using the autoguider port also requires:- An off axis guide scope
- A second CCD camera
- A set of rings and a dovetail for the guide scope
- More weight for a mount that may already be stretched to the limit
As a result, guiding isn't always the answer. For many, the best solution is to improve one's polar alignment to the point that periodic error is the dominant form of tracking error, and then keep the exposure duration limited. Depending on the mount and scope, that may require more than a polar alignment scope can provide. You may need to perform a more accurate drift alignment (which is, I believe, what the original poster is trying to determine).
Personally, with 90s subexposures with the mount and scope described I would be quite happy and would not be trying to refine my polar alignment.
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- Jared Willson
- Fluorostar FLT-110 w/ TEC optics
- Vixen VC200L
- Astro-Physics Mach1 GTO
- Stellarvue SV80S
- Takahashi Teegul SP Mount
- STL-11000
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fuadramsey
member
Reged: 06/26/07
Posts: 49
Loc: Orange County, CA
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Jared,
Thanks that is what I was trying to figure out. Yes I'm sure I'm at the max weight with this mount. I just wanted to know if I could squeeze out another 30 seconds or so. When I drift algined after my polar alignment I did not see any real corrections to be made -the stars stayed fixed. I did not know if I should do it for 5 minutes or use a higher power barlow and illuminated reticle.
Here's some photos I've mananged to capture(DSLR)with this setup (Celestron Omni XLT 150 on the CG-4)and subs: www.yoursweetthyme.com/fuadramsey
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Nils_Lars
scholastic sledgehammer
Reged: 01/04/08
Posts: 903
Loc: Santa Cruz Mountains , CA
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You should have posted those before , I think you have a fine collection of shots going there and there are still quite a few targets you can image if you keep shooting like those.
As far as drift align I always use a 2x Barlow and an illiuminated reticle and let it go 5 min or more and after you do it a few times it gets much easier.
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Erik
Orion ED 80
Orion Atlas GOTO mount
Williams Optics reducer
Various eyepieces and other gear
Baytronix 80mm guidescope
Orion Starshoot Autoguider
PHD guide
Canon 400D (unmodded)
Stilleto Focuser
Tamron 75-300mm&28-80mm lenses
NexImage webcam
http://home.comcast.net/~eriknlarsen/site/?/photos/
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Patrick
Postmaster
Reged: 05/16/03
Posts: 6776
Loc: Franklin, Ohio
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Quote:
I just wanted to know if I could squeeze out another 30 seconds or so. When I drift algined after my polar alignment I did not see any real corrections to be made -the stars stayed fixed.
One way to tell if you're seeing polar alignment 'errors' is to check the position of the stars from subframe to subframe. If you see movement of the stars going across the field, more than likely this is field rotation caused by a mis-polar alignment. If you're NOT seeing blurring in your images but are seeing this movement from frame to frame, it means you're shooting with a short enough focal length and exposure time that the camera is not picking it up. If you want to increase the f/l or exposure length then getting a more accurate polar alignment might help. But at the same time, dec errors may become more prominent as well.
Patrick
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Discovery 10" f/6 Split Tube Dob
Celestron C6 SCT
Denk Binoviewers
AT66ED Refractor
Oberwerk Ultra 15x70 Binocular
475B Geared Tripod & 501HDV Head
Oberwerk 9x60 Binocular
Celestron Regal 8x42 Binocular
Canon 30D DSLR
Mini EQ1
My Astronomy Pages
Edited by Patrick (08/22/08 02:45 PM)
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RandallK
professor emeritus
Reged: 11/10/06
Posts: 713
Loc: Nanaimo, B. C. Canada
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With my HEQ5-Pro, I've "pushed" it to 100 seconds unguided.
All of a sudden, I couldn't even get 20 seconds without trailing but the problem was that the knob that secures the mount head to the tripod was loose! I checked balance which was OK but forgot about the mount head being secure! Of course the other thing is having excellent Polar alignment, something I'm very particular about.
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Scopes: Meade SC-8AT w UHTC
SkyWatcher 5" F/5 Reflector
SkyWatcher 127mm MAK
Mount: HEQ5 Pro
Cameras: Orion Starshoot DS Colour Imager V.1
Imaging Source Webcam DMK21AU04.AS
Palm TX PDA w Astromist and Bluetooth wireles control.
Edited by RandallK (08/22/08 12:48 PM)
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walt r
Carpal Tunnel
Reged: 02/13/07
Posts: 2390
Loc: Doylestown, PA
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The answer really is 'it depends' on:
scope focal length
CCD pixel size
The MOUNT.
With my MAK (@1130mm fl) & cookbook camera on an old Super Polaris mount I can do 2-6 minutes if the exposure is between the PE (periodic error) bumps (worm has a 10 minute period and has a 16arcsec bump once per period). I have standardized on 4 minutes as then most of the exposures miss the PE bump and I throw away a minimum number of subs. I feel this is acceptable for un-guided shots and gives me enough SNR for photometry on stars down to Mag 12 by stacking 6-8 subs.
I do a drift alignment while the scope and camera are cooling. A star will DEC drift only 1/4 of the CCD FOV in 5-6 hours while doing a long time sequence on a short term variable.
You may want to evaluate the PE of your mount by running a sequence of short exposures on a brightish star for 2-4 times your mount's worm period. A sub every 15-30 seconds will provide enough time resolution. When processing the subs have your software extract the X,Y pixel coordinate to a file and import the file into EXCEL. Convert the X,Y pixel coordinate to arc seconds and plot each X and Y vs sub number. Any PE and DEC drift will be easily seen.
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Walt
Obsession 18" f/4.45 #1370 AN/SC
MK67 Deluxe 6" f/12 Mak-Cass, Super Polaris GEM, JMI MicroMax DSC
DIY 60mm f/6 Achromat
Cookbook 245 CCD
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