TV paracorr II 效果不似如期？--update 已有初步測試結果

[LT]

30cm 牛牛第二個辣辣病情：

TV paracorr 比其他 coma corrector 有一個 獨特優點(我個人比較喜歡)，就是多了一個 "travel out"調焦距離，依量度，約20mm。這樣，可設計 牛牛的 焦平面較貼近鏡筒，使100%照亮真徑可以更大，或可使用較細M.A.的副鏡。

菲林年代，使用的第一代paracorr，效果很好，故個人十分喜歡 TV 的這個產品，後來購買第二代。據官方資料，第二代的 coma 修正能力更好，可配合F3.5系統使用。若用於F4系統，效果約等於F8系統。同時，若配合適當的adapter，可大大改善周邊減光問題(35mm菲林上)。

現時數碼單反用的EF鏡亦可用於菲林機上，意味菲林相機的焦平面與數碼單反的是相同或極近似相同。於是便量度菲林相機的焦平面距離，量得48mm。而TV paracorr II 的 back focus 距離是 55mm +-3mm。

於是按計算做了一個adapter將數碼單反接上paracorr II。可是，拍出來的測試照，修正效果很差，顯然是back focus距離未能配合得好，亦有可能paracorr II的修正能力有被誇大之嫌；又或是菲林相機的焦平面距離與數碼機的有所不同。

惟有試試量度數碼單反的焦平面距離，量得44mm左右，原來真的是不相同的(希望量度值是正確的)，於是再製作另一個adapter。拍出來的測試照，修正效果比之前的改善不少，但絕對並不等同F8系統，最多是F6系統。

TV 產品官方資料一向是較可信的，究竟是那一個問題呢？繼續使用 paracorr II，或是轉用Vixen 最新的 coma corrector PH (Wynne type)？若是後者，整個牛牛的身體就需要重做了！

正頭痕中呢。

[Wah!!]

http://www.televue.com/engine/TV3b_page ... inTKX4rLyE
這頁寫的是57mm?

[LT]

http://www.televue.com/engine/TV3b_page ... inTKX4rLyE
這頁寫的是57mm?

另一個令人混淆的資料。

我買的paracorr II 有說明書附送的，內裡寫明back focus 距離 是 55mm +-3mm。究竟信那一個呢？還是十多年前的是55mm，現時的是57mm？

正如現在的383L+ mono CCD，OPT商舖網頁上說它的back focus距離是13mm，但ATIK官方網站資料說是17mm，最後我的量度值是15mm左右，真被 "玩死"。

怎樣量度 coma corrector 的 最佳 back focus 距離呢？

若繼續用這paracorr，看來要 出 最麻煩的絕招來尋求最佳距離配合了！其他同好，可有較好的建議？

[Subaru]

I remember I followed the instructions:
- Paracorr 2: around 55-57mm, cannot remember exactly and need to measure my setup with a micrometer. Anyway, I don't think 2mm makes a huge difference
- Atik 383L+: I suggest to follow the mechanical drawing in the website, i.e. 17.5mm

Here is what I did with a 212mm f/3.9 Newtonian and the Paracorr 2: http://www.hkastroforum.net/viewtopic.p ... &start=410

[LT]

I remember I followed the instructions:
- Paracorr 2: around 55-57mm, cannot remember exactly and need to measure my setup with a micrometer. Anyway, I don't think 2mm makes a huge difference
- Atik 383L+: I suggest to follow the mechanical drawing in the website, i.e. 17.5mm

Here is what I did with a 212mm f/3.9 Newtonian and the Paracorr 2: http://www.hkastroforum.net/viewtopic.p ... &start=410

TV paracorr should show this quality on coma correction. But mine seemed to be a failure one. When did you buy your Type 2?

That back focus distance for digital is quite critical I think. So, 2mm may cause significant difference on correcting coma. I had tried using 17mm back focus distance for my paracorr. But the result was not acceptable. That's why I took a measurement to find out the exact back focus distance of my 383L+.

Hope I can fix the problem once I find out the exact back focus distance of my paracorr.

Anyway, thanks so much for your opinion.

[Subaru]

TV paracorr should show this quality on coma correction. But mine seemed to be a failure one. When did you buy your Type 2?

I remember mine was bought around when it was launched.

[LT]

If my memory is correct, mine should be bought in 2003.

Anyway, I will do testing to find out the "correct distance" between my paracorr and the CCD camera some days later when the sky condition allows.

[Wah!!]

Have asked Televue staffs about your issue?
Maybe you can try daytime bright objects to find the correct distance first.


******
BTW, have you ever tried this glasses before? Does it help?
http://www.enchroma.com/technology/

[LT]

Have asked Televue staffs about your issue?
Maybe you can try daytime bright objects to find the correct distance first.


******
BTW, have you ever tried this glasses before? Does it help?
http://www.enchroma.com/technology/

No and thanks for your suggestion as well as the link. Maybe this product can help me much.

I did think doing the test in daytime but star test should be the most sensitive to display the aberration.

[LT]

初步測試結果：

30cmF4 牛牛 + TV paracorr + Atik 383L 的最佳焦平面距離是 57mm 。

不過受月光、飄雲，極差seeing影響，日後還需確認結果。

引發新問題：為何之前的影像彗差修正會這樣不理想？與加入filters有關嗎？

測試照參考：單張20s @27.5C

[Subaru]

[蔥寶恭喜樣] [蔥寶恭喜樣]