[牧夫天文器材讨論] 新款iOptron SkyTracker迷你星野赤道儀测评

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wtyu21
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[牧夫天文器材讨論] 新款iOptron SkyTracker迷你星野赤道儀测评

文章 wtyu21 » 週一 30 9月, 2013 04:49

國內牧夫天文論壇的帖子,供擁有iOptron Skytracker的用家一個參考!

http://www.astronomy.com.cn/bbs/thread-277773-1-1.html

按帖子樓主評價,此Skytracker精度一般,单軸赤道儀存在周期誤差是正常的,但此Skytracker偏差量超過±35角秒,可能是帖子樓主的單獨案例,不能武斷的說所有Skytracker都有瑕疵,大家可以去看看做個參考!

twahz
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文章 twahz » 週一 30 9月, 2013 10:30

HEQ5也就是正负20角秒的水准,国内一般赤道仪出厂据说不测周期误差的。

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鄧登凳
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文章 鄧登凳 » 週一 30 9月, 2013 15:04

小弟用Nex5 + 180mm鏡拍天球赤道的天體, 每像素5.8角秒, 三分鐘一幅, 沒有拉線。http://www.hkastroforum.net/viewtopic.p ... 5&start=20, 這是改進鎖死底座螺絲前的表現。

另改了杯頭螺絲後, 用支更重的135F2L配500D, 每像素7.2角秒, 也是拍兩三分鐘沒有拉線, 改了螺絲全部100%都可用, 沒有失敗的。

所以, 起碼我那一部週期誤差應是+/-7角秒, 或峰至峰<15角秒。

很大機會牧夫的樓主是那兩口螺絲未收緊 :wink:

LT
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文章 LT » 週一 30 9月, 2013 17:52

" 起碼我那一部週期誤差應是+/-7角秒, 或峰至峰<15角秒。"

Readers, do you think such a small gear in a star tracker is of the same quality of a EM200"s gear? And I don't think you are so lucky to get an exceptionally good sample too. Please look carefully at your star images.

" 此Skytracker精度一般,单軸赤道儀存在周期誤差是正常的,但此Skytracker偏差量超過±35角秒,"

This tested value is more reasonable for a small gear. in fact, that is not a bad one in the test.

No intention to arise any "war" here. But please don't mislead people.

LT



鄧登凳 寫:小弟用Nex5 + 180mm鏡拍天球赤道的天體, 每像素5.8角秒, 三分鐘一幅, 沒有拉線。http://www.hkastroforum.net/viewtopic.p ... 5&start=20, 這是改進鎖死底座螺絲前的表現。

另改了杯頭螺絲後, 用支更重的135F2L配500D, 每像素7.2角秒, 也是拍兩三分鐘沒有拉線, 改了螺絲全部100%都可用, 沒有失敗的。

所以, 起碼我那一部週期誤差應是+/-7角秒, 或峰至峰<15角秒。

很大機會牧夫的樓主是那兩口螺絲未收緊 :wink:

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鄧登凳
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文章 鄧登凳 » 週一 30 9月, 2013 18:53

LT 寫:" 起碼我那一部週期誤差應是+/-7角秒, 或峰至峰<15角秒。"

Readers, do you think such a small gear in a star tracker is of the same quality of a EM200"s gear? And I don't think you are so lucky to get an exceptionally good sample too. Please look carefully at your star images.

" 此Skytracker精度一般,单軸赤道儀存在周期誤差是正常的,但此Skytracker偏差量超過±35角秒,"

This tested value is more reasonable for a small gear. in fact, that is not a bad one in the test.

No intention to arise any "war" here. But please don't mislead people.

LT

Please check the link above, I have already uploaded an 100% crop of the image. Judge for yourself.

If more evidence is required, please check http://www.hkastroforum.net/viewtopic.php?t=28468, there is also an 100% crop there.

Please don't accuse others of "misleading" when you have NOT check the evidence.

twahz
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文章 twahz » 週一 30 9月, 2013 20:55

正负7角秒也不是不可能,毕竟用了那么大的涡轮 。但是是不是每台都正负7角秒,这个我对国货还是持谨慎态度。

lcs9000
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文章 lcs9000 » 週一 30 9月, 2013 21:02

LT 寫:" 起碼我那一部週期誤差應是+/-7角秒, 或峰至峰<15角秒。"

Readers, do you think such a small gear in a star tracker is of the same quality of a EM200"s gear? And I don't think you are so lucky to get an exceptionally good sample too. Please look carefully at your star images.

" 此Skytracker精度一般,单軸赤道儀存在周期誤差是正常的,但此Skytracker偏差量超過±35角秒,"

This tested value is more reasonable for a small gear. in fact, that is not a bad one in the test.

No intention to arise any "war" here. But please don't mislead people.

LT
iOptron Skytracker VS EM200 [烏鴉飛過]

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wtyu21
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文章 wtyu21 » 週二 01 10月, 2013 01:04

lcs9000 寫:
LT 寫:" 起碼我那一部週期誤差應是+/-7角秒, 或峰至峰<15角秒。"

Readers, do you think such a small gear in a star tracker is of the same quality of a EM200"s gear? And I don't think you are so lucky to get an exceptionally good sample too. Please look carefully at your star images.

" 此Skytracker精度一般,单軸赤道儀存在周期誤差是正常的,但此Skytracker偏差量超過±35角秒,"

This tested value is more reasonable for a small gear. in fact, that is not a bad one in the test.

No intention to arise any "war" here. But please don't mislead people.

LT
iOptron Skytracker VS EM200 [烏鴉飛過]
:shock: :shock: :shock:

twahz
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文章 twahz » 週二 01 10月, 2013 10:57

顶顶

LT
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文章 LT » 週二 01 10月, 2013 23:21

twahz 寫:正负7角秒也不是不可能,毕竟用了那么大的涡轮 。但是是不是每台都正负7角秒,这个我对国货还是持谨慎态度。
I cannot say it is absolutely impossible, but 99.999999999% it is impossible for the gear used in that star tracker can reach that said value.

LT
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文章 LT » 週三 02 10月, 2013 00:13

Most EM200 have PE value of about +-6". Not too much can reach +-5". Very seldom owns +-4" and maybe zero copy show PE value so poor that it is more than +-8".

Recalling the film age, it was no problem to get 30 min unguided exposure with a 300mm F2.8 lens with EM200. Even in recent digital years, I think it is no problem too to get 10 min unguided exposure with 300mm lenses, though I haven't done it with digital camera.

Do you think your iOptron star tracker can do so? I really hope our readers can show it out with their proofs.

I absolutely believe your images are real and show evidence there too. Also, you are very great at mathematics. You have no mistake in your working steps and seemed it was very professional. But for the testing approach and the method applied to your analysis, sorry I don't agree anymore.

In the past tens of year of reading articles of testing equatorial mount performance, either in Japanese or English, I haven't seen ONE using the method like yours. Maybe I have been too out-dated and my vision is so narrow too.

Among so many star trackers in the market, I believe only Astrotrac can reach PE value of +-5". Do you know why Astrotrac can do so?

Do you or our fellow astronomy beginners know Edward Byers gears? They had manufactured very excellent gears for those amateur EQ mount builders. The PE value of their 11.5" Master series, without any further special treatment, shows PE value slightly better than +-5". I don't know what size of the gear used in iOptron. But I think it should not be larger than 3.5". For such a low cost gear, how can it be so excellent close to Byer's 11.5" gear?

Readers please test your common sense.

LT

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Wah!!
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文章 Wah!! » 週三 02 10月, 2013 00:24

If the final images that DDD provided are aligned and stacked with softwares, then the error from the images shouldn't be called "PE".
I guess each frames exposure time is not long enough to cover the error peroid of the gear. The error found in the raw images should just be calld "tracking error during the exposure"
To get PE from multiple exposures, the images should be purely stack together WITHOUT alignment, and the total exposure time should be long than the period of the gear.

sampson
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文章 sampson » 週三 02 10月, 2013 01:02

多謝 LT 和 Wah 的講解,對於我哋一大班觀看此天文網站的初階人仕,有多角度和客觀的分析是非常重要的,更難得的是不張狂自大的態度,使初級人仕更願意留步此網站,跟各前輩學習 [Good Job] [Good Job] [Good Job] ,不過我天生愚笨,請不要見怪 [跪拜禮]

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鄧登凳
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文章 鄧登凳 » 週三 02 10月, 2013 01:38

Wah!! 寫:If the final images that DDD provided are aligned and stacked with softwares, then the error from the images shouldn't be called "PE".
I guess each frames exposure time is not long enough to cover the error peroid of the gear. The error found in the raw images should just be calld "tracking error during the exposure"
To get PE from multiple exposures, the images should be purely stack together WITHOUT alignment, and the total exposure time should be long than the period of the gear.
You are correct to say that they are not actual measurement of periodic error. The posted results, one is a single RAW and one is a stacked image represent actually tracking error within a reasonable use, 3 - 2.5 minutes. However, they represent the errors that matter in actual astrophotography.

If one is interested in the theoretic value, here is an image of Lyra which I just stacked again in DSS using "no star alignment option". The stacked image represents more than 40 minutes of tracking (actual is 16 X 2.5 mins, but there are small gaps between each photo). There are more than four cycles of 9.23 mins of 156 teeth wheel. I still cannot see evidence of periodic error within the scale of detectable error in 2 pixels (i.e. less than 15 arc secs).

BTW 15 arc sec PE is not in the region close to the performance of AstroTrac, which I also use. I never assume the skytracker will reach that level. For that reason and for loading issues, I never intend to use a 300mm lens on the iOptron skytracker.

Am I the lucky one with a chance of 0.000000001%? Judge for yourself.
附加檔案
no-alignment-100%.jpg
100% corp of Vega area, scale is 7.2 arc secs per pixel
no-alignment-100%.jpg (908.02 KiB) 已瀏覽 7320 次
no-alignment25%.jpg
No alignment, only stretching in DSS and no other post-processing.
no-alignment25%.jpg (949.81 KiB) 已瀏覽 7320 次

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Wah!!
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文章 Wah!! » 週三 02 10月, 2013 09:09

鄧登凳 寫:If one is interested in the theoretic value, here is an image of Lyra which I just stacked again in DSS using "no star alignment option". The stacked image represents more than 40 minutes of tracking (actual is 16 X 2.5 mins, but there are small gaps between each photo). There are more than four cycles of 9.23 mins of 156 teeth wheel. I still cannot see evidence of periodic error within the scale of detectable error in 2 pixels (i.e. less than 15 arc secs).
Would you mind using the software Startrails to have a second trial?
http://www.startrails.de/html/software.html

I can sure this software does not provide alignment function.


BTW, to test the period error, it's better using stars near Dec 0.
Vega is Dec 39 degrees, which is already quite north, the measured value need to divided by cos(39 degree) as real PE value.

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