LOT 0.55x Reducer


20050725

LOT + Reducer + Narrow band filter 測試  by Astrochild

*注意在F4.4焦比下,窄波段濾鏡中心波長會偏移,且bandpass會變大。

 

M27 H-alpha

 

M27 OIII

 


20050724

LOT + CS45 shutter + 0.55x Reducer Test 

對不掉焦!!! 

PI CCD換大的CS45快門後,新的adapter比原來的增加約 7mm厚度,以致 Reducer鏡組到CCD焦平面距離多了 7mm,超過可調焦範圍。Reducer-CCD之間距離調小7mm,並按 Philipp建議 'Reducer最佳焦點還要再將Reducer-CCD距離調小4mm (you should reduce the distance Camera - Lens by appr. 4mm. Then you should be at the optimim working distance. Optimum working distance is reached at a focal length of 4412mm. But it does not need to be really accurate.)'

總共將 Reducer-CCD之間距離調小10mm後 (此時減焦鏡組突出 adapter 長度 A=120mm),成焦了!用Astrometrica檢查焦長~4356mm。雖然和最佳焦點位置還有些差 (最佳焦長 ~ f.l.=4412mm)  ~So far so good~

 

NGC6823

幾個不同天體測量結果,

[Astrometrica]

Image 1: O:\20050724\NGC6823\R\NGC6823_10s_-007r.fit
Time Stamp: 2005 07 24, 17:45:52 UT
USNO-A2.0: 2984 Records read (31.2' x 30.5')
Astrometry of Image 1 (NGC6823_10s_-007r.fit): 
1144 of 1281 Reference Stars used: dRA = 0.32", dDe = 0.35"
X = -3.352377475E-3 +4.589483422E-6*x -1.897886130E-9*y
Y = +3.388234484E-3 -2.212676319E-9*x -4.589448500E-6*y
Focal Length = 4357.8mm, Rotation = -0.03deg
Pixel Size: 0.95" x 0.95", Field of View: 21.1' x 20.5' 

[PinPoint4]

Plate-solve run at 2005/7/25 01:49:51
O:\20050724\GRB20050724\grb20050724-001r.fit:
Solved using 353 of max 500, RMS residual is 0.31 arcsec, order =4
Roll = -0.013 HScale = -0.949 VScale = -0.949

[Yuji & Kuiyun]

About the reducer system of LOT with PI 1300 CCD camera, I have calculated the asymmetric parameters. (We do not study distortion.) 
The parameters are below.

==============================================
Asymmetric parameters of Reducer with PI1300
                         2005.07.24 Y. Urata
FIT_Keywords   Values
CDELT1         0.000262932183
CDELT2         0.000263017177
CROTA1         -180.067545  
CROTA2         -180.067545  
SECPIX1        -0.9466  
SECPIX2         0.9469
==============================================

 


 

LOT Reducer First Light!      

Horsehead Nebula (IC434)

2005-02-23 14:29:21 (UT)
LOT + 0.5x reducer (D=1,000mm, f.l.=4,350mm) + Ha_6563/30 filter + PI 1300B CCD,  exptime=300sec, Bias/Dark Subtraction only
by Hung-Chin Lin

 

vs. 

LOT direct imaging (without Reducer)

 


Astrometry for LOT+0.5x Reducer

天體測量結果:

Astrometry of 20050223m67-003r.fit by Astrometrica / USNO-A2.0
2005-02-24

545 of 618 Reference Stars used: dRA = 0.33", dDe = 0.30"
X = -2.919105612E-3 +4.589670095E-6*x -2.446183154E-7*y
Y = +3.148480660E-3 -2.451800949E-7*x -4.590348906E-6*y
Center Coordinates: RA = 08h 51m 36.24s, De = +11d48' 21.1"
Focal Length = 4351.1mm, Rotation = -3.06d (i.e. Position Angle=356.94d)
Pixel Size: 0.95" x 0.95", Field of View: 21.2' x 20.5' 


Vignette

LOT + 0.5x Reducer                                                   LOT direct imaging (without reducer)

加減焦鏡前後的周邊減光現象差不多,主要為快門太小遮蔽CCD造成的暗角。


LOT 0.5x Reducer system schema

 

 


LOT直焦點系統裝置圖

 

LOT裝Reducer後會使 CCD焦平面前移約 20cm,因此上圖中的 [175mm] 延長筒及 [4mm] 轉接環都必須移除才對得到焦。因ST-8 CCD guider是掛在[175mm]延長筒上,因此裝Reducer後就不能用offset guider自動導星。可能的解決方法是用同架在LOT上的鏡筒(e.g. ST-8+FLT-100)來導星,但很可能會因LOT主鏡微小偏移而失敗,得實際試試才知道。

注意 LOT+Reducer 要用 reducer專用的 adapter!


LOT + Reducer 系統裝置圖,注意直焦點時用的兩截延長筒都拿掉了!

 

LOT+ Reducer系統圖

請參照上圖,注意 CCD Focal plane到 FilterWheel的 backfocus距離 32mm是包括 "PI1300B-to-SmartFilter adapter 度 (= 6.13mm)" ( PI CCD本身 chip 的 backfocus約~25.7mm [TEO做的adapter為準])。當使用不同CCD相機時因adapter及CCD不同, backfocus也會不一樣。儘量在做 adapter時使所有系統 backfocus儘量一致,避免系統參量(焦長、焦點位置...)變來變去。

 

 

以原始設計 backfocus=105.3953mm為準計算,將A設為 123.2mm時,因受到LOT 調焦範圍 5cm的限制,Move Out到底還是對不到焦的(不夠長)。只得將 Reducer前移,經實測後得到一個可成焦的系統如下:

A=130mm時,使用PI 1300B CCD和ACE SmartFilter,得到LOT+Reducer系統焦長為4350mm,減焦效果約為0.54x。注意成像品質到底如何,才是最重要的!

A = 當B,C固定時,調整A可改變減焦之結果。
B = 為CCD相機本身的 backfocus,因不同CCD而異。
C = 為Reducer到CCD焦平面的backfocus。

 


0.5x Reducer specification

 

 

 

 

 

 

 


LOT 0.5x Reducer adapter

因中央開孔設計太大 (原來給的圖是100mm直徑,但被改大),超出FilterWheel外緣,故會有空隙導致漏光,需用2-3層黑色膠帶貼住。


LOT Reducer的 adapter空隙(紅圈處)會導致漏光,必須遮住


裝 Reducer後看到的 adapter 空隙


更新日期:2005-08-22