Takahashi FSQ 85 ED 光學討論

檢測望遠鏡光學部份,赤道儀機械組件,目鏡配件和拍攝器材 CCD等...
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MANDII
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文章 MANDII » 週二 15 6月, 2010 12:27

PaulNg 寫:
anguslau 寫:
PaulNg 寫:講下講下, 突然間覺得好似同個光學系統既設計有關

A: 有問題既設計--> Petzval 既折射鏡 (再加reducer一樣有問題), 相機鏡頭
B: 冇問題既設計--> 普通折射鏡+flattener

結論: 會唔會係同個"flattener"既設計有關?
A類設計flattener係內置, 即不能隨對焦既動作移動, 同sensor距離可以變.
B類設計flattener外加, 同sensor距離固定.
The problem should not be directly related with a specific design, such as Petzval. It should be directly related to the amount of vignetting inherited in the design.

1) we know that an olived-shaped aperture will produce dark bands

2) we also actually see the olived-shaped aperture shadow in Sing Chai's experiment, directly correlating with the dark bands

3) for any system with vignetting, part of its aperture is blocked; the question is what is the shape of the partially blocked aperture? I believe it is generally olive-shaped for most optical designs; if so, this will produce dark bands similar to the FSQ85

4) if you agree with 3) above, it means most optical systems which exhibits vignetting should have dark band problems; in fact, unless you believe the partially blocked aperture shape is not olive, the characteristic dark band should result
I agree that the proof is pretty convincing... but I've been looking at some images, like this... taken by TMB130 with flattener, 6X7 E200. It shows no dark banding like that...

This can only explain TMB130 can be no problem .
It may not represent the general feature just counting the lens matter .
Besides , the design may be different .
May be it has certain particular design .
Once design matter is involved , it can be any reason is related . And may not be just what you can have a conclution base on 2/3/4 lens matter .
最後由 MANDII 於 週二 15 6月, 2010 12:36 編輯,總共編輯了 3 次。

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Wah!!
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文章 Wah!! » 週二 15 6月, 2010 12:31

若用單組鏡片可以減少軸外阻光, 點解要有 FSQ85 呢類三組設計呢?

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PaulNg
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文章 PaulNg » 週二 15 6月, 2010 12:39

MANDII 寫:
PaulNg 寫: I agree that the proof is pretty convincing... but I've been looking at some images, like this... taken by TMB130 with flattener, 6X7 E200. It shows no dark banding like that...

This can only explain TMB130 can be no problem .
It may not represent the general feature just counting the lens matter .
Besides , the design may be different .
May be it has certain particular design .
Once design matter is involved , it can be any reason is related . And may not be just what you can have a conclution base on 2/3/4 lens matter .
So far Wah's ray diagram can explain all of my observations, speculations, experiences and examples. If you can raise some counter examples that shows the theory is wrong or there are exception cases, we'll be very happy to modify our conclusion.

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willis
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文章 willis » 週二 15 6月, 2010 12:41

PaulNg 寫:Sorry Wah! Sidetrack 少少...

以下係一d 其他牌子既望遠鏡影既相
Pentax 125SDP:

可以見到總之呢類型既 4片glass element Petzval Astrograph就會有咁既情況, 但係正常doublet/triplet 加reducer 就唔會.
PaulNg 寫:講下講下, 突然間覺得好似同個光學系統既設計有關

A: 有問題既設計--> Petzval 既折射鏡 (再加reducer一樣有問題), 相機鏡頭
B: 冇問題既設計--> 普通折射鏡+flattener

結論: 會唔會係同個"flattener"既設計有關?
A類設計flattener係內置, 即不能隨對焦既動作移動, 同sensor距離可以變.
B類設計flattener外加, 同sensor距離固定.
Firstly, I think Paul make a good observation that the Petzval design got the dark band phenomenon, so as the FSQ. At least other doublet or triplet design plus reducer got no or no obvious photos with such phenomenon. The photos, which Paul posted, speak for the design already. Whatever theory or explanation should able to explain this.
Wah!! 寫:想像圖: 假如視場外圍都用上全口徑, 後面的玻璃就要很大很大 (假如光路存在)
Secondly, Wah’s explanation on large rear lens are needed for less vignetting is correct. If the ray diagram provided by Tak is correct, it explained already. However, if a smaller rear lens is used, some light will be blacked. But the point is that the so-called image circle provided by a telescope maker depends on the tolerance. If the tolerance is big, the image circle is large. So without the tolereance, the size of the image circle quoted by the telescope maker may not reliably reflect the vignetting performance. As far as I know top class reducer/flatteners are very big in size. They need 3” or even 3.5” focuser to hold them.

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MANDII
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文章 MANDII » 週二 15 6月, 2010 12:43

PaulNg 寫:
MANDII 寫:This can only explain TMB130 can be no problem .
It may not represent the general feature just counting the lens matter .
Besides , the design may be different .
May be it has certain particular design .
Once design matter is involved , it can be any reason is related . And may not be just what you can have a conclution base on 2/3/4 lens matter .
So far Wah's ray diagram can explain all of my observations, speculations, experiences and examples. If you can raise some counter examples that shows the theory is wrong or there are exception cases, we'll be very happy to modify our conclusion.

How about the camera lens ?
How many lens it has .

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PaulNg
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文章 PaulNg » 週二 15 6月, 2010 12:43

Wah!! 寫:若用單組鏡片可以減少軸外阻光, 點解要有 FSQ85 呢類三組設計呢?
可能好處大過唔好處啦... 可能呢類設計係既離軸星像會容易呈點狀同照明度高, 但係就捨棄左軸外阻光導致既繞射問題

HK.Raymond.Tse
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文章 HK.Raymond.Tse » 週二 15 6月, 2010 12:46

To see whether the darkband diffraction is caused by the FSQ reducer, simply take one photo without reducer with a full frame DSLR or CCD (preferably full film CCD like SB11K) (film or E200 should be not used, since film/E200 is not that sensitive to darkband diffraction) at a bright star and then another one with reducer with the same CCD at the same sky position.

If the darkband diffraction exists only in 1 photo, then the cuplrit is obvious.

If the darkband diffraction exist in both photos, then the FSQ design is problematic.

Do one control with a F6 refractor (with and without field flattener) using the same large format CCD at the same bright star.

Then the odds should be obvious after comparing 4 of such photos.

Dear Dr. Tong, if you want to conduct a shootout test of FSQ (both 106ED & 85ED would be nice/Refractor, please let me know, as I am considering a FSQ at the moment.

Raymond Tse

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PaulNg
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文章 PaulNg » 週二 15 6月, 2010 12:46

MANDII 寫:
PaulNg 寫: So far Wah's ray diagram can explain all of my observations, speculations, experiences and examples. If you can raise some counter examples that shows the theory is wrong or there are exception cases, we'll be very happy to modify our conclusion.

How about the camera lens ?
How many lens it has .
We have mentioned a few examples, like Canon 135 F/2, 328 F2.8, and my own photos using Canon 400 F5.6 also has this problem.

The optical path of camera lenses are too complicated to draw conclusion from i believe.

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MANDII
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文章 MANDII » 週二 15 6月, 2010 12:52

PaulNg 寫:
We have mentioned a few examples, like Canon 135 F/2, 328 F2.8, and my own photos using Canon 400 F5.6 also has this problem.

The optical path of camera lenses are too complicated to draw conclusion from i believe.

I already said previously .
optic structure can be a reason .
Optic parameters ( what we said in this thread previously ) , e.g F-ratio , flame size ,etc .. is also a reason .
Under the same optic structure , above Optic parameters apply samely .

I can't see what problem here so far talking .

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Wah!!
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文章 Wah!! » 週二 15 6月, 2010 12:53

HK.Raymond.Tse 寫:....If the darkband diffraction exist in both photos, then the FSQ design is problematic.
....
I think the double-fan shape diffraction pattern still exist even without a reducer, based on the light path diagram from Takahashi.
I actually don't think it is a big problem :P

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willis
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文章 willis » 週二 15 6月, 2010 12:56

HK.Raymond.Tse 寫:To see whether the darkband diffraction is caused by the FSQ reducer, simply take one photo without reducer with a full frame DSLR or CCD (preferably full film CCD like SB11K) (film or E200 should be not used, since film/E200 is not that sensitive to darkband diffraction) at a bright star and then another one with reducer with the same CCD at the same sky position.

If the darkband diffraction exists only in 1 photo, then the cuplrit is obvious.

If the darkband diffraction exist in both photos, then the FSQ design is problematic.

Do one control with a F6 refractor (with and without field flattener) using the same large format CCD at the same bright star.

Then the odds should be obvious after comparing 4 of such photos.

Dear Dr. Tong, if you want to conduct a shootout test of FSQ (both 106ED & 85ED would be nice/Refractor, please let me know, as I am considering a FSQ at the moment.

Raymond Tse
昇仔's photos showed already that the dark band occured in both with and without reducer.

http://www.hkastroforum.net/viewtopic.p ... &start=135

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Wah!!
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文章 Wah!! » 週二 15 6月, 2010 13:10

最後個疑惑仲係度, 點解光錐形狀在焦點前後不同呢?
係唔係因為調整相機時, 不是只有相機本身移動, 還包括了其他光學部份(例如第四片玻璃)????

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willis
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文章 willis » 週二 15 6月, 2010 13:18

Wah!! 寫:最後個疑惑仲係度, 點解光錐形狀在焦點前後不同呢?
係唔係因為調整相機時, 不是只有相機本身移動, 還包括了其他光學部份(例如第四片玻璃)????
It seems that all four lens element are mounted on the tube & the focuser moves alone. Or FSQ users help to confirm this.
附加檔案
FSQ-85EDtube.jpg
FSQ-85EDtube.jpg (112.36 KiB) 已瀏覽 3589 次

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sn-10
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文章 sn-10 » 週二 15 6月, 2010 13:21

the 3rd and 4th elements do not move.

LT
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文章 LT » 週二 15 6月, 2010 13:53

Suggest to make such a aperture mask as shown in the attachment and place it in front of any refracting telescope and then take a shot of point source with a little overexposure.

Maybe the answer would come out immediately after checking the on-axis image.

Wish suggestion working.

LT
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Assymetric mask.doc
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