Tuesday, October 25, 2011

PHD dec drift

PHD dec drift by edhiker
PHD dec drift, a photo by edhiker on Flickr.

I was sent this document by Celestron, to be distributed freely. Edhiker
.................................................
Mechanical backlash (as differentiated from gear backlash) is caused by static friction. Typically on the order of a few arcseconds, mechanical backlash is only seen when making small position adjustments in the same direction with a complete stop between each adjustment. This situation occurs frequently during pulse guiding. Mechanical backlash can make it appear that your mount is “stuck” and unable to guide in Declination. (It doesn’t apply to RA because that axis doesn’t stop moving between guiding pulses.) This document describes methods to help combat mechanical backlash while pulse guiding

Tip #1
The mechanical backlash can be increased or decreased dramatically (a factor of 2 or more) with a gravitational assist. For example, suppose the star in your image is drifting to the north in DEC. If you hang a small weight on one end of the tube so that it tends to pull north, this will keep the gears pre-tensioned in that direction. Thus the mechanical backlash in that direction will be less. Of course, mechanical backlash in the other direction will be worse by the same amount, but since changing direction also requires overcoming the gear backlash, which is many times larger, it won’t be noticed. Don’t get carried away though, too much weight can cause serious overshoot of the DEC axis when it first starts to slide. Start small and work upwards.
If this trick is not possible (as is the case in a remote observatory) then you must make sure your tube is well balanced in DEC. Don't let it become heavy in the direction of North or South. Rebalance it after you change camera equipment. The “Set Mount Position” function in the Utilities menu can be used to accomplish this without losing your alignment.

Tip #2:
Auto guiding software has multiple parameters that can help you address mechanical backlash. It is different in every package. One such parameter allows you to set the maximum pulse duration. This must be long enough to overcome the mechanical backlash on your system. If you can't control maximum duration, try increasing the AG rate setting with you hand control. Another setting to look for is the one that controls the minimum displacement before acting. For example, say you have a mount with a mechanical backlash of 3 arcSeconds. If you set the software to require a minimum of 3.5 arcseconds before reacting it will be sure to send a pulse long enough to overcome the mechanical backlash plus a little bit more. Of course, the net displacement of the mount, after accounting for the mechanical backlash, will be only 0.5 arcSeconds, and the drift error will still be 3.0 seconds. But once error rises to 3.5 arcSeconds, the software will again send a pulse of 3.5 arcSeconds, and you get another net gain of 0.5 arcSeconds. Thus, the mount will move in tiny steps of 0.5 arcSeconds, but always 3.0 arcSeconds behind. As long as you start your exposure after first correction from the AG software, the star will not drift during your exposure by more than 0.5 arcSeconds.

FINAL NOTE:
Mechanical backlash has been around for a long time. Using tips like the ones I described above, successful imagers have worked around mechanical backlash for many years.
Ref: mechanical backlash5.doc

Wednesday, August 24, 2011

Our ( edhiker ) vacation pictures at Rock Creek are at https://picasaweb.google.com/101865043104641583028/RockCreekAug242011?authuser=0&authkey=Gv1sRgCLHcrpy_nLPIDw&feat=directlink

Rock Creek, Aug 17-23, 2011
Shows how it was on above dates.

Photos from Edhiker's belt camera - unedited, except re-sized. A few rotated 90ยบ. Three more cameras to go...

Located in Rock Creek Canyon is East Fork Campground. This beautifully wooded area is dense with aspens, pine, and fir trees
Reservations http://www.reserveamerica.com/campgroundDetails.do?subTabIndex=0&&contractCode=nrso&parkCode=easf


My 2009 and 2010
pictures of Rock Creek are at http://www.flickr.com/photos/edhiker/sets/72157624579779954/ and http://www.flickr.com/photos/edhiker/sets/72157621950726691/

My campsite location at http://www.flickr.com/photos/edhiker/3834565955/

GPS Info. (Latitude, Longitude): 37.48361, -118.7175


Weather http://forecast.weather.gov/MapClick.php?lat=37.470498470798724&lon=-118.72787475585938&site=rev&unit=0&lg=en&FcstType=text



Tuesday, August 02, 2011

2009 P1 Garradd X15 - levels cropped 3349-8132

Sample history
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H:\Astro2011\ST-8300\Aug1 esp comet\Comet 5 300s 18in f4 CLS only MPCC_001.fit
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H:\Astro2011\ST-8300\Aug1 esp comet\Comet 5 300s 18in f4 CLS only MPCC_005.fit
Saving H:\Astro2011\ST-8300\Aug1 esp comet\2009 P1 Garradd x15 stack no-darks.fit
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Crop from 638,362 to 2640,1872
Demosaic image
DDP: Bkg=11351 Xover=20498 B-Power=0.92 Sharp=3
Saving H:\Astro2011\ST-8300\Aug1 esp comet\2009 P1 Garradd - 15 - just for fun DDS.jpg
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Multi-set pre-processing begun
Processing light set 1 -- 15 lights to process
Dark: H:\Astro2011\ST-8300\Darks\_-_ Dark Master 27x 300sec at -15C.fit
Flat: (filt=0)
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Pre-process images
H:\Astro2011\ST-8300\Darks\_-_ Dark Master 27x 300sec at -15C.fit loaded as dark
Pre-processing images...
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H:\Astro2011\ST-8300\Aug1 esp comet\Comet 3 300s 18in f4 CLS only MPCC_005.fit
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H:\Astro2011\ST-8300\Aug1 esp comet\pproc_Comet 4 300s 18in f4 CLS only MPCC_004.fit
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H:\Astro2011\ST-8300\Aug1 esp comet\pproc_Comet 5 300s 18in f4 CLS only MPCC_001.fit
H:\Astro2011\ST-8300\Aug1 esp comet\pproc_Comet 5 300s 18in f4 CLS only MPCC_002.fit
H:\Astro2011\ST-8300\Aug1 esp comet\pproc_Comet 5 300s 18in f4 CLS only MPCC_003.fit
H:\Astro2011\ST-8300\Aug1 esp comet\pproc_Comet 5 300s 18in f4 CLS only MPCC_004.fit
H:\Astro2011\ST-8300\Aug1 esp comet\pproc_Comet 5 300s 18in f4 CLS only MPCC_005.fit
Saving H:\Astro2011\ST-8300\Darks\Comet X15 stacked on stars.fit
Crop from 1140,740 to 2128,1468
Saving H:\Astro2011\ST-8300\Aug1 esp comet\2009 P1 Garradd x15 darks - stack on stars crop .fit
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Loading H:\Astro2011\ST-8300\Aug1 esp comet\2009 P1 Garradd x15 darks - stack on stars crop .fit
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H:\Astro2011\ST-8300\Aug1 esp comet\recon_pproc_Comet 5 300s 18in f4 CLS only MPCC_001.fit
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H:\Astro2011\ST-8300\Aug1 esp comet\recon_pproc_Comet 5 300s 18in f4 CLS only MPCC_003.fit
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H:\Astro2011\ST-8300\Aug1 esp comet\recon_pproc_Comet 5 300s 18in f4 CLS only MPCC_005.fit
Saving H:\Astro2011\ST-8300\Aug1 esp comet\Comet CLS filter pproc X15 then Batch - batch Demosaic Stacked on comet.fit
Undo!
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HSL: H=0.000 S=0.480 L=0.000
Crop from 674,416 to 2640,1827
Saving H:\Astro2011\ST-8300\Aug1 esp comet\2009 P1 Garradd X15 - levels cropped 3349-8132.jpg
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Curves: 62,118 and 103,284
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Loading H:\Astro2011\ST-8300\Aug1 esp comet\Comet 4 300s 18in f4 CLS only MPCC_002.fit
Demosaic image
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Color offset: R=0 G=239 B=318
HSL: H=0.000 S=0.100 L=0.000
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Loading H:\Astro2011\ST-8300\Aug1 esp comet\6960 3 1000s 12in fl and reducer OIII _001.fit
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Loading H:\Astro2011\ST-8300\Aug1 esp comet\2009 P1 Garradd X15 - levels cropped 3349-8132.jpg

Thursday, March 31, 2011

edhiker's photostream

OAG pickoff and relay assy on cameraTwo PHD autoguide instances in XP laptop - star with graphTwo autoguiders , testing on power poleWebCam set for long exposureWebCam set for short exposurePar-focalized off-axis guider and guide camera
Alex - eve to rememberAutoguided astro imaging setup using a webcamBig 12 day moonM3 globular cluster, cropM45 crop - Shack autoguider test Flowers near Mission Peak
Tree on Mission Peak HikeHike up grassSanta Clarita Park MapShack Autoguider on scopeShack Gigaware Webcam - exposure rangeWebcam driver has EXPOSURE control, read on...
Astrophoto setup with Shack AutoguiderRadioShack WebcamShack Webcam - lens screws offTaurus stars, eight minutesM51 with 102mm f5 , exposure 375 secondsM51,  8 min exposure from Los Angeles

LED lighting for a hotel, $430k , payback in 17 months.
How do they compute payback? Compact florescence is used now. Does duty cycle enter into the math?
48" tube = $50 http://dkledlights.com/