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 17:38

Dear Angus ,

I know we are actually looking at different point of view . You and all others are looking at the indepth technical optics , I just looking at a point of view of common person .

Can you give me a comment on my below point of view , whether it's correct or not correct in my below 3 points ? You can even simply say "WRONG" or "totally WRONG" if you like or you can give explaination in more detail , actually I don't mind . Surly don't mind .

I just want to know the answer only . Or any other person is willing to give comments . I welcome as well .

PLEASE !


MANDII

*********************************************

Optic physical structure = number of lens , lens curvature , light path or what ever physically .

Optic paramters = ( source brightness ,focal length/ratio , camera flame size etc .. . what we had dicussed . )

1. Optic strcuture is a fixed factor . It cannot explian the different levels of dark band in a same sope system .
Our previous findings all shows there is a trend/levels of Dark bands . In FSQ 85 it has this case , Even in FSQ 106 it also has this case , and these trend changes with optic paramters .


2. Number of lens is just one of the optic structure factor , Paul raise up the number of lens( 3 or 4 lens easily cause Dark bands ) is the cause . Then , he should catagories all scopes into number of lens( 1&2 or 3&4) , and find out that those 3&4 lens scopes uses can cause Dark bands . But so far , we only see one example of TMB300 scope(1/2 lens) . Although this show the difference , but still not strong enough to say the number of lens is related with Dark bands . Thus , we still cannot denie the possibility of other factors of optic structure .

3. Within a same optic physical strcuture , optic paramters applys samely to determine the levels of dark bands .


The difference is :
In case 1 , we only need to provide 1 or 2 example to prove this .

In case 2 , we need to provide many examples to prove this .

anguslau
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文章 anguslau » 週二 15 6月, 2010 17:38

鄧登凳 寫:
昇仔 寫:
I use mostly Taka connectors following Taka's system diagram for FSQ 85. The M42 ring is used to connect the camera.

For the setting without the reducer, an extension tube is used. This is not exactly the same as Taka diagram but it is said that the tube is produced by Taka anyway.
Strange! I do not know why Takahashi use a T2 ring (42mm screw) in its light path for something intended for full frame...
The connector train which uses the T42 adapter is adapted from a visual config. Not suitable for imaging, particularly for full-frame 35mm cameras. The T42 adapter will definitely introduce significant vignetting since it only has ~36mm clear aperture, there is no way it can cover a 44mm image circle with good illumination! In addition, the 70S occular adapter uses a thumbscrew to secure the long train behind is not secure enough and prone to introduce flexure. IMO, this config should be avoided at all cost.

If you look at the system chart, there is another config which uses the wide-T mount adapter and all connections are screw mounts. This is a much better and more secure train for imaging.

This is one of the reason I do not like the FSQ106 config without the CAA. I really hate thumb screw connections. For the FSQ106, I also found the focuser draw tube extending too much given its "standard" adapters, I asked tan14 to make new adapters for me so that the drawtube never need to extend more than 10mm.

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昇仔
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文章 昇仔 » 週二 15 6月, 2010 17:40

anguslau 寫:
鄧登凳 寫:
昇仔 寫:
I use mostly Taka connectors following Taka's system diagram for FSQ 85. The M42 ring is used to connect the camera.

For the setting without the reducer, an extension tube is used. This is not exactly the same as Taka diagram but it is said that the tube is produced by Taka anyway.
Strange! I do not know why Takahashi use a T2 ring (42mm screw) in its light path for something intended for full frame...
The connector train which uses the T42 adapter is adapted from a visual config. Not suitable for imaging, particularly for full-frame 35mm cameras. The T42 adapter will definitely introduce significant vignetting since it only has ~36mm clear aperture, there is no way it can cover a 44mm image circle with good illumination! In addition, the 70S occular adapter uses a thumbscrew to secure the long train behind is not secure enough and prone to introduce flexure. IMO, this config should be avoided at all cost.

If you look at the system chart, there is another config which uses the wide-T mount adapter and all connections are screw mounts. This is a much better and more secure train for imaging.

This is one of the reason I do not like the FSQ106 config without the CAA. I really hate thumb screw connections. For the FSQ106, I also found the focuser draw tube extending too much given its "standard" adapters, I asked tan14 to make new adapters for me so that the drawtube never need to extend more than 10mm.
I am using the wide-T mount adapter. Perhaps I confused the name in my previous message.

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鄧登凳
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文章 鄧登凳 » 週二 15 6月, 2010 17:43

Wah!! 寫:I think "Light path.JPG" maybe over-simplified:
1. Light cone projecting to the edge is not full aperture of the primary lens.
2. Light cone projecting angle may not be the same as the drawing.
The path may be simplified. However the angle of the light cone reaching the focal plain should obey to rule of f-ratio, shouldn't it?

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Wah!!
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文章 Wah!! » 週二 15 6月, 2010 17:48

鄧登凳 寫:The path may be simplified. However the angle of the light cone reaching the focal plain should obey to rule of f-ratio, shouldn't it?
The angle I mean is the cone axis direction, not the width of the cone.

anguslau
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文章 anguslau » 週二 15 6月, 2010 18:12

willis 寫:We can also find the FSQ-106 info. The image circle of FSQ-106 is:
44mm (luminosity is 60%) (With reducer or extender)
http://www.takahashijapan.com/ct-produc ... 106ED.html

Which means Tak defines the tolerance of the image circle is 60% luminosity.
I believe luminosity is one factor but probably not the most important criteria for image circle definition. People probably focus more on spot sizes in their design. But it does look like keeping luminosity level >60% within the image circle is Tak's design goal.

Just measured some luminosity data on my FSQ106 flats (35mm full-frame sensor):
Without reducer: corner=80% long edge=90%
0.73x reducer: corner=63% long edge=82%
1.6x extender: corner=61% long edge=71%

I consider illumination is excellent without reducer, and very good with 0.73x reducer since a major portion has >80% luminosity. I did not observe obvious dark bands for both configs.

Actually comparing with the data for FSQ85, illumination for FSQ85 without reducer is quite similar (evenly slightly better) to FSQ106+0.73x. But I haven't observed obvious dark bands yet in actual imaging. Perhaps I will given the bright stars in the right locations... :roll: Anyway, I think once we get to know the limitations, I don't think this is a big deal. And I am happy to live with it. :wink:

anguslau
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文章: 1167
註冊時間: 週五 15 4月, 2005 20:18

文章 anguslau » 週二 15 6月, 2010 18:30

MANDII 寫:Dear Angus ,

I know we are actually looking at different point of view . You and all others are looking at the indepth technical optics , I just looking at a point of view of common person .

Can you give me a comment on my below point of view , whether it's correct or not correct in my below 3 points ? You can even simply say "WRONG" or "totally WRONG" if you like or you can give explaination in more detail , actually I don't mind . Surly don't mind .

I just want to know the answer only . Or any other person is willing to give comments . I welcome as well .

PLEASE !


MANDII

*********************************************

Optic physical structure = number of lens , lens curvature , light path or what ever physically .

Optic paramters = ( source brightness ,focal length/ratio , camera flame size etc .. . what we had dicussed . )

1. Optic strcuture is a fixed factor . It cannot explian the different levels of dark band in a same sope system .
Our previous findings all shows there is a trend/levels of Dark bands . In FSQ 85 it has this case , Even in FSQ 106 it also has this case , and these trend changes with optic paramters .


2. Number of lens is just one of the optic structure factor , Paul raise up the number of lens( 3 or 4 lens easily cause Dark bands ) is the cause . Then , he should catagories all scopes into number of lens( 1&2 or 3&4) , and find out that those 3&4 lens scopes uses can cause Dark bands . But so far , we only see one example of TMB300 scope(1/2 lens) . Although this show the difference , but still not strong enough to say the number of lens is related with Dark bands . Thus , we still cannot denie the possibility of other factors of optic structure .

3. Within a same optic physical strcuture , optic paramters applys samely to determine the levels of dark bands .


The difference is :
In case 1 , we only need to provide 1 or 2 example to prove this .

In case 2 , we need to provide many examples to prove this .
Sorry, I have difficulty understanding your questions or statements. Not sure I can add any more. I suggest not to worry too much about the details behind. Simply put, if a scope has vignetting (most have some), it may show dark bands for bright stars. More vignetting, more prominent dark bands.

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鄧登凳
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文章 鄧登凳 » 週二 15 6月, 2010 18:43

Wah!! 寫:欖核形光斑已被證實, 證明雙扇形光芒是由繞射而來.

但是最有趣的地方是焦點前後的光斑並不對稱, 不知是何原因? :? :? :? :? :?
比較個系統的焦前圖和焦後圖的燈柱粗度, 焦前圖的焦距差誤都些焦後圖的差誤小。

而街燈本身是長形的。

如果有圓形燈的影, 就可以估計下那個阻光的東西佔光錐的多少百分比?

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willis
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文章 willis » 週二 15 6月, 2010 18:52

anguslau 寫: I believe luminosity is one factor but probably not the most important criteria for image circle definition. People probably focus more on spot sizes in their design. But it does look like keeping luminosity level >60% within the image circle is Tak's design goal.

Just measured some luminosity data on my FSQ106 flats (35mm full-frame sensor):
Without reducer: corner=80% long edge=90%
0.73x reducer: corner=63% long edge=82%
1.6x extender: corner=61% long edge=71%

I consider illumination is excellent without reducer, and very good with 0.73x reducer since a major portion has >80% luminosity. I did not observe obvious dark bands for both configs.

Actually comparing with the data for FSQ85, illumination for FSQ85 without reducer is quite similar (evenly slightly better) to FSQ106+0.73x. But I haven't observed obvious dark bands yet in actual imaging. Perhaps I will given the bright stars in the right locations... :roll: Anyway, I think once we get to know the limitations, I don't think this is a big deal. And I am happy to live with it. :wink:
There is no judgement here. But knowing that 昇仔's test result agree with Tak's factory definition. I think luminosity is most important factor to define the image circle. Otherwise, why do Tak stated it next to the size of the image circle? If it is not important to define image circle, what else? And how it related to calculate the image circle?

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MANDII
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文章 MANDII » 週二 15 6月, 2010 19:03

anguslau 寫: Sorry, I have difficulty understanding your questions or statements. Not sure I can add any more. I suggest not to worry too much about the details behind. Simply put, if a scope has vignetting (most have some), it may show dark bands for bright stars. More vignetting, more prominent dark bands.
Ok, 8) I see .
That's a difference of technical person and a non-technical person .
Thank you very much indeed and I can understand what you mean here now .
:wink:

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Subaru
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文章 Subaru » 週二 15 6月, 2010 19:13

Basically, diffraction spikes or dark band is more visible when there is a 尖角 as the obstacle, or the diffraction will spread around when the edge is a smooth one.

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Wah!!
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文章 Wah!! » 週二 15 6月, 2010 19:18

Subaru 寫:Basically, diffraction spikes or dark band is more visible when there is a 尖角 as the obstacle, or the diffraction will spread around when the edge is a smooth one.
Agree, the diffraction flare/spikes shape only related to the SHAPE of the edges, not related to the vignetting seriousness.

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Subaru
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文章 Subaru » 週二 15 6月, 2010 19:22

昇仔 寫:
anguslau 寫:
Subaru 寫:This phenomena does not only apply to Petzval, but also on telephoto design.

I was using a low cost 400mm f/5.6 telephoto lens some 2x years ago for DSO photography with film, and noticed this effect, thus it is something rather common, and I believe it is not treated as a problem in the field of astrophotography.
Now it looks obvious that this phenomenon is not that uncommon. Perhaps we were just expecting too much and over-reacting a little. :lol: But I guess people just tend to expect text book stars when paying for premium gears such as a Tak astrograph... :wink:
We talk like we are over-reacted, at least for people looking at these discussions. For me I am just curious. And we are already making textbook stars or something close to that quality. :wink:
I guess this phenomenon was not widely discussed, and it is interesting to study the nature and the reason behind this effect.

The telescope or astrograph is just a tool, and it can't break the law of Physics. Even the more advanced Schmidt cameras has some drawbacks like severe internal reflection, which some people may love the flare produced.

anguslau
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文章: 1167
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文章 anguslau » 週二 15 6月, 2010 19:24

Wah!! 寫:
Subaru 寫:Basically, diffraction spikes or dark band is more visible when there is a 尖角 as the obstacle, or the diffraction will spread around when the edge is a smooth one.
Agree, the diffraction flare/spikes shape only related to the SHAPE of the edges, not related to the vignetting seriousness.
Agreed! But why I say that is because as vignetting becomes more severe, the olive shape is more elongated and has sharper ends. Hence the diffraction spikes more prominent. Of course, there are a few assumptions here.

Anyway, I think discussions over the last couple of days has been fruitful and I believe I have much better understanding of the issue now. :D

KS
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註冊時間: 週四 26 7月, 2007 09:36

文章 KS » 週二 15 6月, 2010 21:07

Wah!! 寫:有無辦法係焦平面, 用個細鏡頭的相機/WEBCAM 影返向主鏡方向呢? 可能會見到邊個位置對於光作出遮擋.
唔知這兩張圖對這次討論有無用?
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