Astrodon Modified 5DII first light

[willis]

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

[社長]

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。

[willis]

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.

[社長]

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.

[vr2il]

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

[willis]

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!