搜索
查看: 3853|回復: 6

M42 - my first image for 2008

 關閉 [複製鏈接]
發表於 2008-1-4 00:35:40 | 顯示全部樓層 |閱讀模式
Can't resist the clear skies over the past few days. Below is my first image for this year - M42 in narrowband. Here are some technical details:
Image #1: Ha=13x600s, O3=4x600s, S2=4x600s; for the core: Ha=O3=S2=3x120s
Image #2: Ha of the above image - for Andy
Equipment: EF600/4, EM-200, ST-2000XM self-guided, Astrodon filters
TnScRt_M42 HOS 600S_1P5.jpg
M42 Ha 20080101 p2.jpg
發表於 2008-1-4 00:53:39 | 顯示全部樓層
一直都有個想法,賣左d takahashi鏡,買番支600/f4或400/f2.8,
用途多d唔洗禁浪費
 樓主| 發表於 2008-1-4 16:53:22 | 顯示全部樓層
原帖由 ianchung 於 2008-1-4 00:53 發表
一直都有個想法,賣左d takahashi鏡,買番支600/f4或400/f2.8,
用途多d唔洗禁浪費

There are advantages and disadvantages. Based on my experiences so far:

1) Its very light and compact compared to same aperture telescope; the 600/4 is only about 6kg and I can hand carry it on an airplane with a photopack, yet it has 6" aperture
2) You can autofocus on bright stars with a DSLR, very convenient in the field and no need to carry laptop and/or focuser for fine focusing
3) field is very flat up to 35mm format
4) can use teleconverters to extend focal length, they are parfocal too
5) contrast and sharpness not as good as an APO scope
6) bright stars tend to flare with peculiar shapes
7) back focus distance is very short (44mm for Canon, Nikon slight longer); may not be enough for large CCD cameras with filter wheels
8) fine manual focus by hand very difficult; I use a RoboFocus which is satisfactory
9) stars not round if not critically focused; pronounced aberrations of various kinds will appear even when focus is slight off; so accurate focus is very critical

Overall, I still think it is excellent for astro-photo on travel. You only need the mount, the lens + DSLR to make the simplest setup for unguided photog. During the day, you can use the lens & DSLR for birds and other stuff too.
發表於 2008-1-5 00:52:04 | 顯示全部樓層
RGB = SII Ha OIII?

Great shot!
發表於 2008-1-5 01:44:30 | 顯示全部樓層
Great shot! Thanks for testing 684
 樓主| 發表於 2008-1-5 15:23:29 | 顯示全部樓層
原帖由 Astroandy 於 2008-1-5 00:52 發表
RGB = SII Ha OIII?

I usually use RGB = Ha OIII SII
So my composites have a strong red and green tone. I found SII usually very weak for most objects.
 樓主| 發表於 2008-1-5 15:30:10 | 顯示全部樓層
原帖由 BillYeung 於 2008-1-5 01:44 發表
Great shot! Thanks for testing 684

Thanks, Bill!

I have been trying out my three long lenses (300/2.8, 400/4, 600/4) on various objects. They all show similar characteristics in terms of quality and usage behaviour. However, I had some problem with my 300/2.8. Not sure if it is because of its faster f ratio or the quality of my specific copy, I found its optical quality not as good as the other two lenses. Stars are slightly coma shaped (particularly those away from the center). It is also much more difficult to focus than the f/4 lenses. IMO, the two f/4 lenses produces satisfactory results for wide angle shots.

[ 本帖最後由 anguslau 於 2008-1-5 15:31 編輯 ]
您需要登錄後才可以回帖 登錄 | 申請討論區帳戶

本版積分規則

手機版|Archiver|香港天文學會  

GMT+8, 2019-8-18 05:22 , Processed in 0.039222 second(s), 10 queries , Redis On.

Powered by Discuz! X3.4

© 2001-2013 Design S!|平潭

快速回復 返回頂部 返回列表