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revans
Carpal Tunnel
Reged: 09/26/05
Posts: 1514
Loc: Fitchburg, MA
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Being mostly a lunar person, I haven't really tested the accuracy of my Tak EM-200 mount much in the past. Lately though, I've become more interested in learning deep sky again and have been working for now without an autoguider. I have found, through fairly careful testing that my Losmandy G11 mount allows 5 minutes at FL=600 with a simple alignment using the polar finder scope and without drift aligment and without an autoguider. This is really good... but my Tak EM-200 mount allows a better polar alignment and I think it is probably close to the 2 arc minutes claimed in the manual. Just doing a simple polar alignment using the polar scope and no drift aligning and no autoguider, I can image for 10 to 15 minutes at FL=500 without seeing any significant star trailing.
I think that is fairly amazing... having used a Meade LXD75 mount for years which was capable of 30 seconds of accurate tracking and no more... 
Anyway... High praise is in order to the folks at Takahashi ! 
PS - I didn't use PEC with either mount... just the basics...
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Rick Evans
http://www.freewebs.com/revans_01420/
"The universe is there for us to see, but it cannot be understood without learning its language -- mathematics." Galileo Galilei
Edited by revans (10/19/09 10:14 PM)
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bardo
member
Reged: 09/13/09
Posts: 49
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guess thats why they're 10X the price of a lxd75
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amateur
sage
Reged: 06/15/06
Posts: 300
Loc: The Netherlands
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I simulate a trail of about 4x4 pixels worst case, with
PE= 4 arc sec amplitude (8 arcsec peak to peak)
polar alignment error = 2 arc minutes
f=500mm
t=15 minutes
pixelsize=5.6 microns
Startrails simulator
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revans
Carpal Tunnel
Reged: 09/26/05
Posts: 1514
Loc: Fitchburg, MA
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Interesting simulation... my somewhat old Canon DSLR camera image size is 3072 x 2048 pixels. Do I understand correctly that with that format star trails would only amount to 4 pixels long? Probably I haven't understood correctly? But if I do understand then re-scaling the image to my usual 640 x 480 or so pixel dimensions during processing would produce star trails of only a pixel at 15 minutes at FL=500?
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Rick Evans
http://www.freewebs.com/revans_01420/
"The universe is there for us to see, but it cannot be understood without learning its language -- mathematics." Galileo Galilei
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amateur
sage
Reged: 06/15/06
Posts: 300
Loc: The Netherlands
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If you bin to 640 x 480 your pixels will effectively become 3072/640 = 5 times larger and thus the PE and polar alignment trail 5 times smaller expressed in pixels. So 3.5 pixels/5 = no visible trailing at 640x480 at all.
You can simply fill in 35 microns as pixel size (7.4 mu for Canon D60(?) x 5 times binning) to get the same result: less than one pixel drift+PE
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