请教：用PAM调极轴碰到的第二个问题——测量重复性
最近一直研究如何用PAM调极轴，前几天在PAM的辅助下，将极轴精度调到了接近1角分，本来以为可以结束学习了，没想到昨天碰到了新问题：1. 用PAM测量分析，调整极轴后，再次测量极轴偏离更多了
2. 怀疑PAM测量的重复性，于是在同一位置反复测量，结果发现每次结果都不同，有时偏差很大，达到了几个角分。在此情况下，根据测量结果调极轴是没有意义的。
3. 检查了赤道仪和主镜、导星镜、导星ccd、三脚架等各个部件的连接紧固程度，锁紧程度，连接都很紧，没发现问题。
4. 在多个起始位置反复测量，结果都是如此。
设备如下：zeq25+cf90+60/240导星镜+asi120mc导星ccd
从PAM记录的LOG中抽取连续三次测量的日志如下：
22:22:47 Start Alignment Run
22:22:47 Plate solve method is PinPoint
22:22:47 Selected catalog is GSC-1.1
22:22:47 Telescope Slew is 6 degrees
22:22:47 Exposure is 6 sec
22:22:47 Telescope at RA = 03:30:14Dec = 59?59' 19"
22:22:47 ***** Exposing Image 1 *****
22:22:49 Start Solving Plate 1
22:22:51 Step 1: Found 801 objects in image.
22:22:51 Plate Solve Attempt at RA = 03:30:14Dec = 59?59' 19"
22:22:51 Step 2: Look up catalog stars for area...
22:22:51 Step 2: Found 612 catalog stars in area.
22:22:51 Step 3: Solve the plate...
22:22:52 Solved using 71 stars, average residual is 1.09 arcsec, order =4
22:22:52 Solution took 3.1 seconds
22:22:52 RA = 03h 29m 01.482s3.48374507
22:22:52 Dec = 59° 56' 19.23"59.938675
22:22:52 Roll = -0.785 HScale = 3.407 VScale = 3.408 Binning = 1
22:22:52 RA Error = -0.020144
22:22:52 Dec Error = -0.049936
22:22:53 Plate 1 Solved
22:22:53 Plate 1 RA = 03:29:01
22:22:53 Plate 1 Dec = 59?56' 19"
22:23:00 Telescope at RA = 3.10389Dec = 59.98861
22:23:06 ***** Exposing Image 2 *****
22:23:07 Start Solving Plate 2
22:23:08 Step 1: Found 706 objects in image.
22:23:08 Plate Solve Attempt at RA = 03:05:01Dec = 59?56' 19"
22:23:08 Step 2: Look up catalog stars for area...
22:23:08 Step 2: Found 612 catalog stars in area.
22:23:08 Step 3: Solve the plate...
22:23:09 Solved using 55 stars, average residual is 1.17 arcsec, order =4
22:23:09 Solution took 2.1 seconds
22:23:09 RA = 03h 05m 04.357s3.08454365
22:23:09 Dec = 59° 55' 35.33"59.926480
22:23:09 Roll = -0.860 HScale = 3.406 VScale = 3.407 Binning = 1
22:23:09 RA Error = -0.019345
22:23:09 Dec Error = -0.062131
22:23:10 Plate 2 Solved
22:23:10 Plate 2 RA = 03:05:04
22:23:10 Plate 2 Dec = 59?55' 35"
22:23:18 Telescope at RA = 02:42:14Dec = 59?59' 19"
22:23:24 ***** Exposing Image 3 *****
22:23:25 Start Solving Plate 3
22:23:26 Step 1: Found 627 objects in image.
22:23:26 Plate Solve Attempt at RA = 02:41:07Dec = 59?54' 51"
22:23:26 Step 2: Look up catalog stars for area...
22:23:26 Step 2: Found 672 catalog stars in area.
22:23:26 Step 3: Solve the plate...
22:23:27 Solved using 52 stars, average residual is 1.01 arcsec, order =4
22:23:27 Solution took 2.1 seconds
22:23:27 RA = 02h 41m 09.115s2.68586533
22:23:27 Dec = 59° 54' 58.23"59.916176
22:23:27 Roll = -0.828 HScale = 3.411 VScale = 3.408 Binning = 1
22:23:27 RA Error = -0.018024
22:23:27 Dec Error = -0.072436
22:23:28 Plate 3 Solved
22:23:28 Plate 3 RA = 02:41:09
22:23:28 Plate 3 Dec = 59?54' 58"
22:23:28 A = 0.0025C = 1.0000Theta = 6.2807
22:23:28 Gamma = 0.0024
22:23:28 Elevation error: -8.57 arc-min
22:23:28 Azimuth error: -10.96 arc-min
22:23:28 Error Amplitude = 0.1999 Degrees from Pole (Dec units)
22:23:28 Error Angle = 224.4771 Degrees CCW from Up
22:23:28 RA Offset = -0.0417, Dec Offset = -0.107
22:23:35 Telescope at RA = 3.50389Dec = 59.98861
22:23:35 Operation stopped by operator
22:23:35 Align Aborted
22:23:41
22:23:41 Start Alignment Run
22:23:41 Plate solve method is PinPoint
22:23:41 Selected catalog is GSC-1.1
22:23:41 Telescope Slew is 6 degrees
22:23:41 Exposure is 6 sec
22:23:41 Telescope at RA = 03:30:14Dec = 59?59' 19"
22:23:41 ***** Exposing Image 1 *****
22:23:43 Start Solving Plate 1
22:23:44 Step 1: Found 834 objects in image.
22:23:44 Plate Solve Attempt at RA = 03:30:14Dec = 59?59' 19"
22:23:44 Step 2: Look up catalog stars for area...
22:23:44 Step 2: Found 612 catalog stars in area.
22:23:44 Step 3: Solve the plate...
22:23:46 Solved using 76 stars, average residual is 1.06 arcsec, order =4
22:23:46 Solution took 2.6 seconds
22:23:46 RA = 03h 28m 58.367s3.48287984
22:23:46 Dec = 59° 56' 18.23"59.938397
22:23:46 Roll = -0.811 HScale = 3.408 VScale = 3.411 Binning = 1
22:23:46 RA Error = -0.021009
22:23:46 Dec Error = -0.050214
22:23:47 Plate 1 Solved
22:23:47 Plate 1 RA = 03:28:58
22:23:47 Plate 1 Dec = 59?56' 18"
22:23:53 Telescope at RA = 3.10389Dec = 59.98861
22:23:59 ***** Exposing Image 2 *****
22:24:01 Start Solving Plate 2
22:24:02 Step 1: Found 768 objects in image.
22:24:02 Plate Solve Attempt at RA = 03:04:58Dec = 59?56' 18"
22:24:02 Step 2: Look up catalog stars for area...
22:24:02 Step 2: Found 610 catalog stars in area.
22:24:02 Step 3: Solve the plate...
22:24:03 Solved using 60 stars, average residual is 1.34 arcsec, order =4
22:24:03 Solution took 1.8 seconds
22:24:03 RA = 03h 05m 04.650s3.08462512
22:24:03 Dec = 59° 55' 34.90"59.926361
22:24:03 Roll = -0.882 HScale = 3.412 VScale = 3.402 Binning = 1
22:24:03 RA Error = -0.019264
22:24:03 Dec Error = -0.062250
22:24:04 Plate 2 Solved
22:24:04 Plate 2 RA = 03:05:05
22:24:04 Plate 2 Dec = 59?55' 35"
22:24:12 Telescope at RA = 02:42:14Dec = 59?59' 19"
22:24:17 ***** Exposing Image 3 *****
22:24:19 Start Solving Plate 3
22:24:20 Step 1: Found 633 objects in image.
22:24:20 Plate Solve Attempt at RA = 02:41:11Dec = 59?54' 52"
22:24:20 Step 2: Look up catalog stars for area...
22:24:20 Step 2: Found 670 catalog stars in area.
22:24:20 Step 3: Solve the plate...
22:24:21 Solved using 54 stars, average residual is 1.25 arcsec, order =4
22:24:21 Solution took 2.3 seconds
22:24:21 RA = 02h 41m 09.893s2.68608132
22:24:21 Dec = 59° 54' 54.60"59.915167
22:24:21 Roll = -0.882 HScale = 3.416 VScale = 3.417 Binning = 1
22:24:21 RA Error = -0.017808
22:24:21 Dec Error = -0.073444
22:24:22 Plate 3 Solved
22:24:22 Plate 3 RA = 02:41:10
22:24:22 Plate 3 Dec = 59?54' 55"
22:24:22 A = 0.0022C = 1.0000Theta = 6.2810
22:24:22 Gamma = 0.0009
22:24:23 Elevation error: -7.41 arc-min
22:24:23 Azimuth error: -3.88 arc-min
22:24:23 Error Amplitude = 0.1330 Degrees from Pole (Dec units)
22:24:23 Error Angle = 201.8811 Degrees CCW from Up
22:24:23 RA Offset = 0.0312, Dec Offset = -0.013
22:24:30 Telescope at RA = 3.50389Dec = 59.98861
22:26:27 Operation stopped by operator
22:26:27 Align Aborted
22:26:28
22:26:28 Start Alignment Run
22:26:28 Plate solve method is PinPoint
22:26:28 Selected catalog is GSC-1.1
22:26:28 Telescope Slew is 6 degrees
22:26:28 Exposure is 6 sec
22:26:28 Telescope at RA = 03:30:14Dec = 59?59' 19"
22:26:28 ***** Exposing Image 1 *****
22:26:31 Start Solving Plate 1
22:26:32 Step 1: Found 960 objects in image.
22:26:32 Plate Solve Attempt at RA = 03:30:14Dec = 59?59' 19"
22:26:32 Step 2: Look up catalog stars for area...
22:26:32 Step 2: Found 612 catalog stars in area.
22:26:32 Step 3: Solve the plate...
22:26:34 Solved using 81 stars, average residual is 1.08 arcsec, order =4
22:26:34 Solution took 3.1 seconds
22:26:34 RA = 03h 29m 00.442s3.48345607
22:26:34 Dec = 59° 56' 14.85"59.937458
22:26:34 Roll = -0.826 HScale = 3.409 VScale = 3.411 Binning = 1
22:26:34 RA Error = -0.020433
22:26:34 Dec Error = -0.051153
22:26:35 Plate 1 Solved
22:26:35 Plate 1 RA = 03:29:00
22:26:35 Plate 1 Dec = 59?56' 15"
22:26:42 Telescope at RA = 3.10389Dec = 59.98861
22:26:48 ***** Exposing Image 2 *****
22:26:49 Start Solving Plate 2
22:26:50 Step 1: Found 711 objects in image.
22:26:50 Plate Solve Attempt at RA = 03:05:00Dec = 59?56' 15"
22:26:50 Step 2: Look up catalog stars for area...
22:26:50 Step 2: Found 613 catalog stars in area.
22:26:50 Step 3: Solve the plate...
22:26:51 Solved using 74 stars, average residual is 1.35 arcsec, order =4
22:26:51 Solution took 2.2 seconds
22:26:51 RA = 03h 05m 03.571s3.08432521
22:26:51 Dec = 59° 55' 32.13"59.925592
22:26:51 Roll = -0.759 HScale = 3.410 VScale = 3.408 Binning = 1
22:26:51 RA Error = -0.019564
22:26:52 Dec Error = -0.063019
22:26:53 Plate 2 Solved
22:26:53 Plate 2 RA = 03:05:04
22:26:53 Plate 2 Dec = 59?55' 32"
22:27:00 Telescope at RA = 02:42:14Dec = 59?59' 19"
22:27:06 ***** Exposing Image 3 *****
22:27:07 Start Solving Plate 3
22:27:08 Step 1: Found 660 objects in image.
22:27:08 Plate Solve Attempt at RA = 02:41:07Dec = 59?54' 49"
22:27:08 Step 2: Look up catalog stars for area...
22:27:08 Step 2: Found 672 catalog stars in area.
22:27:08 Step 3: Solve the plate...
22:27:09 Solved using 46 stars, average residual is 1.07 arcsec, order =4
22:27:09 Solution took 2.4 seconds
22:27:09 RA = 02h 41m 10.253s2.68618140
22:27:09 Dec = 59° 54' 53.35"59.914820
22:27:09 Roll = -0.877 HScale = 3.414 VScale = 3.415 Binning = 1
22:27:09 RA Error = -0.017707
22:27:09 Dec Error = -0.073792
22:27:10 Plate 3 Solved
22:27:10 Plate 3 RA = 02:41:10
22:27:10 Plate 3 Dec = 59?54' 53"
22:27:10 A = 0.0022C = 1.0000Theta = 6.2809
22:27:10 Gamma = 0.0012
22:27:11 Elevation error: -7.69 arc-min
22:27:11 Azimuth error: -5.18 arc-min
22:27:11 Error Amplitude = 0.1443 Degrees from Pole (Dec units)
22:27:11 Error Angle = 207.3293 Degrees CCW from Up
22:27:11 RA Offset = -0.0777, Dec Offset = -0.034
22:27:17 Telescope at RA = 3.50389Dec = 59.98861
22:28:14 Operation stopped by operator
22:28:14 Align Aborted
从日志中可以看出，三次测量的极轴误差分别是：
(1) Elevation error: -8.57 arc-min，Azimuth error: -10.96 arc-min
(2) Elevation error: -7.41 arc-min Azimuth error: -3.88 arc-min
(3) Elevation error: -7.69 arc-minAzimuth error: -5.18 arc-min
可见结果的重复性很差。
请PAM的高手帮我分析分析这是怎么回事？另外，昨晚风比较大，大概有4级，我是在阳台里测量的，器材本身受风的影响不大，但是视宁度较差，和这个有关系吗？
@northwolfwu
Telescope at RA = 03:30:14Dec = 59?59' 19"
不要用靠近北极星位置的天区，最好的位置是中大陆南靠东面，一般我是取仰角40~60度，水平角在140~160度附近的亮星作为初始位置。 谢谢，主要是在阳台里角度受限制，明天我出去试试 mayapple 发表于 2014-3-21 02:41
谢谢，主要是在阳台里角度受限制，明天我出去试试
能看到北极星的话还是用极轴镜对极轴，精度也不错，对于短焦绰绰有余了。 northwolfwu 发表于 2014-3-21 08:58
能看到北极星的话还是用极轴镜对极轴，精度也不错，对于短焦绰绰有余了。 ...
我的赤道仪是zeq25，用极轴镜的话，有时候很准，导星精度很高，有时候不准，没查明白为什么，所以才想试试别的方法来提高精度。
再问您一个问题，我仔细看了上面的PAM日志后，发现测试时，三次曝光的过程中，每次RA减小十度后，DEC也有微小的变化，每次减小了0.01度，PAM程序里应该不会控制DEC减小吧？我想可能是赤道仪本身机械刚度的问题？dec的变化会不会影响测试结果？想查找PAM的算法，没找到，所以请您帮着分析分析。
mayapple 发表于 2014-3-21 09:53
我的赤道仪是zeq25，用极轴镜的话，有时候很准，导星精度很高，有时候不准，没查明白为什么，所以才想试 ...
实际的DEC有变化（pinpoint解析）就对了，因为极轴存在误差。 northwolfwu 发表于 2014-3-21 11:41
实际的DEC有变化（pinpoint解析）就对了，因为极轴存在误差。
对对，明白了
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