Takahashi FSQ 85 ED 光學討論

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anguslau
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Takahashi FSQ 85 ED 光學討論

文章 anguslau » 週五 11 6月, 2010 15:03

Great attempt and congrat on the new instruments! :D I'm sure it will get even better if you can capture more frames next time... :wink:

It is a sad fact of life for HK imagers that we need to go overseas in order to get some decent astro photos. Since most of us can only afford doing that a few times a year, we need to make the best use of our time there. I think our best bet is to plan as carefully and as details as we can before hand and try to simplify our setup and procedures to ensure that our time under the stars are mostly productive rather than fixing all sorts of problems. Unfortunately, while we are trying to figure out the best setup and processes, we need to experiment and this can take up much of our precious travelling times. When we wasted a lot of time due to various unexpected problems, I guess we can look at it positively since we know we can probably avoid repeating the same mistakes on subsequent trips. :lol:

I notice that the brightest stars in your image display some peculiar flare patterns. It is very similar to my previous attempts in the past. I always thought that they are due to some abberration of Canon long lenses. Since now you are using the FSQ85, I now suspect such flares are coming from DSLRs... :roll:


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Wah! 分割文章自:
http://www.hkastroforum.net/viewtopic.php?t=19588

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PeterPeter
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文章 PeterPeter » 週五 11 6月, 2010 15:59

anguslau 寫:....I notice that the brightest stars in your image display some peculiar flare patterns. It is very similar to my previous attempts in the past. I always thought that they are due to some abberration of Canon long lenses. Since now you are using the FSQ85, I now suspect such flares are coming from DSLRs... :roll:
May I know are you talking about the following two stars (as shown in pictures A & B) :roll:

Pictures 1 & 2 indicate the similar phenomenon in set-up of Nikon 300mm lens + Canon 350D.
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B.jpg
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最後由 PeterPeter 於 週五 11 6月, 2010 16:20 編輯,總共編輯了 1 次。

anguslau
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文章 anguslau » 週五 11 6月, 2010 16:19

PeterPeter 寫:
anguslau 寫:....I notice that the brightest stars in your image display some peculiar flare patterns. It is very similar to my previous attempts in the past. I always thought that they are due to some abberration of Canon long lenses. Since now you are using the FSQ85, I now suspect such flares are coming from DSLRs... :roll:
May I know are you talking about the following two stars :roll:
Yes, exactly.

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Wah!!
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文章 Wah!! » 週五 11 6月, 2010 16:31

Does such pattern appear in night scene photos?

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PeterPeter
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文章 PeterPeter » 週五 11 6月, 2010 16:46

上面的圖片1 和 2 是剪輯自以下相片.

都希望怏些有個答案
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複製 -2010年5月14日清晨 天蠍座 M4及部分調色盤-2 b.jpg
複製 -2010年5月14日清晨 天蠍座 M4及部分調色盤-2 b.jpg (123.48 KiB) 已瀏覽 20315 次

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昇仔
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文章 昇仔 » 週五 11 6月, 2010 17:17

I am not quite sure if it is a problem with the FSQ :? . It might be artifacts caused by processing. When a curve is applied to the blue channel but not the other two channels, the blue color at a certain brightness level may be enhanced more than the other two colors :roll:

I will check my original image again. :D

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MANDII
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文章 MANDII » 週五 11 6月, 2010 17:23

see the source photo , better .. .
In order we can distinguish the causes of this problem .
I guess mostly the processing matter .. .

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昇仔
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文章 昇仔 » 週五 11 6月, 2010 17:29

anguslau 寫:Great attempt and congrat on the new instruments! :D I'm sure it will get even better if you can capture more frames next time... :wink:

It is a sad fact of life for HK imagers that we need to go overseas in order to get some decent astro photos. Since most of us can only afford doing that a few times a year, we need to make the best use of our time there. I think our best bet is to plan as carefully and as details as we can before hand and try to simplify our setup and procedures to ensure that our time under the stars are mostly productive rather than fixing all sorts of problems. Unfortunately, while we are trying to figure out the best setup and processes, we need to experiment and this can take up much of our precious travelling times. When we wasted a lot of time due to various unexpected problems, I guess we can look at it positively since we know we can probably avoid repeating the same mistakes on subsequent trips. :lol:
Totally agree, let's accept these problems look at them positively so that we can prepare our trips more carefully and in details in the future. But it is a pity that the weather in HK sometimes doesn't even allow us to test our equipments. Testing on guiding, for example, requires at least some stars to be seen. But in HK you may not be able to see the stars for a month or two. :cry: Simplifying the setup and processes are also very important. Trivial things like fixing screws etc. may become time consuming (or difficult in the dark) during a oversea trip.

Hope that we slowly form a team to support each others in overseas trips :P

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Wah!!
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文章 Wah!! » 週五 11 6月, 2010 17:29

昇仔 寫:I am not quite sure if it is a problem with the FSQ :? . It might be artifacts caused by processing. When a curve is applied to the blue channel but not the other two channels, the blue color at a certain brightness level may be enhanced more than the other two colors :roll:

I will check my original image again. :D
I don't think the problem is caused by processing.
The dark bands are symetric to the center of the image, I bet it is a problem within the optical path.

I suggest you to shoot street lights to see if can reproduce the problem.

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昇仔
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文章 昇仔 » 週五 11 6月, 2010 17:32

Wah!! 寫:
昇仔 寫:I am not quite sure if it is a problem with the FSQ :? . It might be artifacts caused by processing. When a curve is applied to the blue channel but not the other two channels, the blue color at a certain brightness level may be enhanced more than the other two colors :roll:

I will check my original image again. :D
I don't think the problem is caused by processing.
The dark bands are symetric to the center of the image, I bet it is a problem within the optical path.

I suggest you to shoot street lights to see if can reproduce the problem.
What do you mean by dark bands?
Do you mean that two bands that divide the stars into half?
I also want to know the origin of the bands but it may not be related to the color flare????

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Wah!!
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文章 Wah!! » 週五 11 6月, 2010 17:34

http://hkastroforum.net/files/_2010514_ ... _b_916.jpg

Can you see dark bands go through bright stars along yellow arrows directions?

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昇仔
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文章 昇仔 » 週五 11 6月, 2010 17:35

Wah!! 寫:http://hkastroforum.net/files/_2010514_ ... _b_916.jpg

Can you see dark bands go through bright stars along yellow arrows directions?
See, that is also what I meant.

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Wah!!
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文章 Wah!! » 週五 11 6月, 2010 17:41

I suggest:
1. Reproduce the problem with distant street lights
2. Use a circle mask to change the aperture, see if the problem persists.
3. Use different lens/scopes (@max F ratio) to see if the problem persists

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昇仔
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文章 昇仔 » 週五 11 6月, 2010 17:42

Wah!! 寫:I suggest:
1. Reproduce the problem with distant street lights
2. Use a circle mask to change the aperture, see if the problem persists.
3. Use different lens/scopes (@max F ratio) to see if the problem persists
See, let's try.

anguslau
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文章 anguslau » 週五 11 6月, 2010 17:50

If you look at a similar photo I took last year, you can see the problem more easily since it is much more obvious in my photos. Below are the original photo and crops of the bright stars. :roll:
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080629_Antares_240x10_328_M5D_Stars.jpg
100% crops of some bright stars
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080629_Antares_240x10_328_M5D_v1.jpg
The original photo
080629_Antares_240x10_328_M5D_v1.jpg (145.28 KiB) 已瀏覽 20430 次

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