www.astrocafe.hk

在香港大部分的Canon DSLR都是用上Baader的天文濾鏡改裝。少部分又可能是唯一的Hutech IDAS天文濾鏡改裝機可能是社長的5DII。早前發現Astrodon有出Canon DSLR的天文濾鏡，就非常感興趣，因為Astrodon是一間出色的濾鏡製造商。

http://www.astrodon.com/products/filter ... side_dslr/

根據Astrodon的網頁，Astrodon在減去紫外線和近紅外線的表現是競爭對手的2000倍！更加使我心動！

You can also see that the Astrodon Inside filter blocks all UV and Near-IR light. In the Near-IR, we only transmit 0.003%, whereas acompetitor's filter lets 6% Near-IR light pass to the sensor. That's 2000 times less for the Astrodon Inside filter.

但以我所知，香港沒有人試過，所以寫電郵去問清楚。收到Astrodon的清晰回覆後就決定把濾鏡訂回來。上星期收到濾鏡後立即拿去改裝！好彩在前晚(28/6)8:00pm把改裝了的5DII取回，把握到半年難得的清天，北潭涌去也！這是第一張開光照，不能有太多的結論，但紅光的反應是明顯增強了的。

器材：APM-TMB 105/650, Riccardi Super ED 0.75X Reducer, Astrodon Modified 5DII, LVI II, HEQ5Pro
目標：北美星雲
拍攝數據：ISO 1600, 28oC, 6x@4 mins, 暗場 4x@4 mins
照片後製：DSS, PS

那你的結論是?

我的關注點和你不同，我更關注ghost image及star halo的表現，有機會拍張馬頭星雲及M45看看。

看你的照片有一點我不太舒服，因為這減焦鏡在全片幅的角上失光只有3%，你就算Histogram stretch太狠也不應看到暗角，是否在filter用上M48的LPS濾鏡? 我發現用M52的會明顯好些的。

Yes! The smaller size 48mm filter really affect the vignetting. If one have budget should go for 52mm. I bought my 48mm filter when I only have APM-LOMO 80/480. It is a waste to buy a new 52mm filter. Maybe when I buy a new V4, I will go for 52mm. The other alternative is Ben's arrangement. Use a 72mm filter in front of the flattener (I not sure about his filter size. Anyway it is a big one). There is no need to care about the back focus shift also. The other reason is that part of the light is blocked by Canon camera body. Don't u remember I told u before that if I use Nikon, there is no vignetting in both full-frame & APS size. The Canon camera, especially full frame, the vignetting is more significant. As u are using CCD now, there is no blocking at all.

willis 寫:Yes! The smaller size 48mm filter really affect the vignetting. If one have budget should go for 52mm. I bought my 48mm filter when I only have APM-LOMO 80/480. It is a waste to buy a new 52mm filter. Maybe when I buy a new V4, I will go for 52mm. The other alternative is Ben's arrangement. Use a 72mm filter in front of the flattener (I not sure about his filter size. Anyway it is a big one). There is no need to care about the back focus shift also. The other reason is that part of the light is blocked by Canon camera body. Don't u remember I told u before that if I use Nikon, there is no vignetting in both full-frame & APS size. The Canon camera, especially full frame, the vignetting is more significant. As u are using CCD now, there is no blocking at all.

Canon's vignetting is not at corner.

Placing LPS filter in front of the reducer will help minimizing ghost reflection also.

請問 willis 兄 5DII 改機後平常拍攝時自動對焦焦點準確嗎? 聽 Tan14 說這片 filter 比原廠 filter 厚了 0.2mm

I asked this question to Astrodon before I order the filter. She said that the thickness is different but the refractive index compensated it. As a matter of fact, I used my Astrodon modified 5D II to do regular photography in my Taiwan trip in summer. No problem!