In search of partner, flattener, for APM-LOMO 80/480

[willis]

Last summer I started DSI. The myth of APM is ever rest in my head! This all start with a casual terrestrial observation with an APM-LOMO 80/600. The razor sharp and high contrast image is really striking. Visually I cannot detect any false color. Later I got another chance to try my friend's APM-LOMO 80/480. It is equally striking. Even you point the scope to distant artificial spotlight. I doubt you can detect any false color. Well visually these two scopes are of winner in 80mm class. However, these two scopes got no custom made flatteners. Perhaps most people use TV 0.8X as the flattener. This has been mentioned in APM's website, but I found that the performance of TV 0.8X on APM-LOMO 80/480 in the case of full-film is average. At the extreme corner, it shows both chromatic and spherical aberrations. I found this last summer, when I borrowed my friend’s APM-LOMO 80/480 for my Taiwan trip. However, it would be fine for APS size.
viewtopic.php?f=17&t=380
http://willisao.blogspot.com/2010/07/ha ... -trip.html

At the same time, there is report about TV 0.8X should be optimized for the APM-LOMO 80s. The term optimized means the back focus between the flattener and the CCD should be adjusted. But it seems that no concrete data can be found in the Internet. At the other size, the life of APM-LOMO 80/600 is much easier. The TS 2 performance on full-film is just plug-and-play. I used APM 80/600 and TS 2 to produce my very first DSI last July, the performance is just gorgeous. With my bad skills & no stacking etc, the single frame image is decent and showed point sharp performance at the full-frame corners.
viewtopic.php?f=17&t=365

Well, what I need is an ultimate tool which capable to deliver both the top visual enjoyment & top photographic performance. In this case the FSQs are off, the optical design is optimized for astrophotography and the built-in flattener cannot be detached, the visual performance is sacrificed. For those who experience that will know it:
http://www.hkastroforum.net/viewtopic.php?t=18550

So the question is can a traditional APO design which deliver top visual performance be converted to top performance astrograph with a good matched flattener. For those who really owned or tried would know the answer is obviously “YES”. However, those flatteners are specially made by the same telescope maker. But for APM-LOMO 80/480 and 80/600 is not, as Thomas Back didn't design one for these two little orphans before he pass away. So one to experience and see if there is third party flattener works for APM 80/480 and APM 80/600.

Yesterday xiaoer and I got a chance to play around with this mix and match game. Due to the running out of the 5DII battery, we only played this game on APM-LOMO 80/480. We will probably play this game on APM-LOMO 80/600 later.

The game is really time consuming as we need to try different optimization, different back focus. Before the flattener test, we first do the star test. I don't mention too much about the star test, as it is textbook like. During the flattener experiment, the artificial star of 50um is placed 23.5m away and we turned on all three red, green & blue LEDs. The angle is 0.044 arc sec which is much smaller that the theoretical resolution limit of a 80mm scope for visible light. Therefore the artificial star is virtually a point source. We took two photos for each setting. One is at the centre and the second one is at the upper left corner of the field of view of 5DII. We have tested 5 flatteners, TS 2, TV 0.8X, SW 0.85 (80ED version), Borg 7887 and AstroTech. Both TS2 and AstroTech are zero power flatteners. Here is the result (APM LOMO 80-480 Flattener Test.jpg). All are 100x100 & 100% crop from the original photos.

The result obtained is not fine tuned yet. If one really wants to find the better result, down to 0.5 mm back focus adjustment is needed. As we don't have all the spacers of different diameters, we cannot do this at the moment. But this reason certainly gives a good guideline and hint for selecting and optimizing the flattener for the APM/LOMO 80/480. This result makes this scope to be a excellent astrograph.

For the zero power flattener, the best option is TS 2. (**The data for TS 2 is not back focus adjustment, but back focus) For the reducer/flattener, the best option is Borg 7888. At the moment we found this, both xiaoer & I were shocked! How come the corner performance of full-film DSLR can be that great! It just like cloning the centre stars to the corner! Thre is one tricky point to note for the Borg 7887 is that there are two positions in the Borg 7887 to place the spacer. Different locations have different performance. According to our finding, the 1 mm spacer should be placed at the rear position of the flattener. The TV 0.8X & SW 0.85X are also good. In fact we have tested the off-centre performance. For the APS size, both TV 0.8X and SW 0.85X are very good. The AstroTech seems not a good match for the APM 80/480, although we tried to adjust the back focus up to 10.5mm already.

So the final verdict is if you are going to do full-film with APM/LOMO 80/480, TS 2 and Borg 7887 are the flatteners to buy.

PS* Thanks社長 (Savio) for lending the flatteners and 5DII for us to do this test.

[社長]

謝謝Willis, 十分詳盡的測試報告

Last summer I started DSI. The myth of APM is ever rest in my head! This all start with a casual terrestrial observation with an APM-LOMO 80/600.

不要忘記，望遠鏡光學是一個系統工程，目鏡是另外一半故事，頂級鏡頭還是要極品目鏡配合的。那次我給你用的目鏡是TMB Aspheric Orthoscopic 25mm，相信二手價不會低於600美元。

At the other size, the life of APM-LOMO 80/600 is much easier. The TS 2 performance on full-film is just plug-and-play. the single frame image is decent and showed point sharp performance at the full-frame corners.
viewtopic.php?f=17&t=365

也不是純Plug and play的，我的80/600跟TS2也粗略量過一下才用，當然我相信仍未優化的。

Well, what I need is an ultimate tool which capable to deliver both the top visual enjoyment & top photographic performance.
So the question is can a traditional APO design which deliver top visual performance be converted to top performance astrograph with a good matched flattener. For those who really owned or tried would know the answer is obviously “YES”.

若一個國家只有一種宗教，那便會導至極權；若天文圈內只許容一種聲音，一個品牌，那便產生謬誤。其實 Astrocafe 就是要透過各項測試、報告，讓大家看到"攝星儀"並非深空攝影的唯一或最完美的答案，在這裡也會看到很多香港及各地的天文建設，星空派對等，是沒有在其他渠道發表過的。

Yesterday xiaoer and I got a chance to play around with this mix and match game. Due to the running out of the 5DII battery, we only played this game on APM-LOMO 80/480. We will probably play this game on APM-LOMO 80/600 later.

Why not? 不如就在年初三、四吧，若有機會找到一台FSQ85ED或FSQ106ED對照一下會更好玩。

the artificial star of 50um is placed 23.5m away and we turned on all three red, green & blue LEDs. The angle is 0.044 arc sec which is much smaller that the theoretical resolution limit of a 80mm scope for visible light. Therefore the artificial star is virtually a point source.

從解像度看，人工星點已足夠細小。論距離測試，約焦距的50x，雖然不是無限遠，但也算可以：
http://www.telescope-optics.net/star_te ... escope.htm

但日後還是要在星空下作實際拍攝，以中等ISO曝光最少5至10分鐘以上才可作結實，因為有些暗淡的色差問題，是有機會在那情況下顯現出來的，雖然經過室內人工星點測試後，基本已確保問題不會太嚴重。

Here is the result (APM LOMO 80-480 Flattener Test.jpg). All are 100x100 & 100% crop from the original photos.

唯一兩項意見：

1. 日後若能配合魚骨版及電子調焦，比較星點大小會更客觀，這個測試我看比較像差色差很有用，但對星點解像度未能作結論，一來非無限遠的人工星點仍會引入一些球面像差，二來若沒有把焦準量化，我們不能結論出不同平場鏡的解像度高低。

2. 抱歉我認為最後一幅圖右面 "Back Focus" 的標註有些誤導，那應該是測試時，我們加入的額外後焦距。例如TS2的5mm，應是我常用的接環額外拉長5mm，實際平場鏡框平面至焦平面應是112mm，若用單鏡反光機拍攝，機身加T Ring是標準的55mm，即接環要57mm長。以BORG 7887計，那1mm即是要在平場鏡及相機接環中加入一片1mm厚的墊片。

[社長]

Willis, 突然想起一件事，我手上還有一些Sky Watcher新出的universal flattener，不如下次把這個也測試一下

[sharkfin]

Very good experiment!
look forward for further investigations

Then I can 坐響其成 and pick the best flattener for my 80/480

[willis]

Very good experiment!
look forward for further investigations

Then I can 坐響其成 and pick the best flattener for my 80/480

Sorry! I guess u need to buy two, not one. TS2 & Borg 7887. These two can provide two focal length for u. Mind ur wallet.

[社長]

Sorry! I guess u need to buy two, not one. TS2 & Borg 7887. These two can provide two focal length for u. Mind ur wallet.

或許sharkfin暫時用7887好些，因為他是用4/3片幅，像場不夠大。

[社長]

Very good experiment!
look forward for further investigations

Then I can 坐響其成 and pick the best flattener for my 80/480

榮耀歸 Willis

大半年前sharkfin你選購望遠鏡時，曾引起一陣”品牌之爭”，這件事我瞭解的，也感謝你的信任。

這個測試只是履行了我的承諾：會找一個比TV 0.8x更好的平場鏡給你，以便日後上全片幅時用。或許你日後拍深空時，可以跟當時提及不同品牌及型號的望遠鏡對照一下，以驗證我跟你分享過的訊息。

[Lewis]

Very detailed experiment , especially for a Physics Teacher .

So, we can buy a best combination of flattener and telescope without "Try and Error".

[David]

Then I can 坐響其成 and pick the best flattener for my 80/480

Yes, and luckily I got my 7887 a long time ago which just happens to be the best one to match my 80/480.

Since I usually use my 80/480 for visual use and only occasionally used for photography, it is no good for me to buy an astrograph and then another scope for visual. The best for me is to buy a good visual scope, and then add a flattener to make it good for photography when I need to take pictures. Also, the total cost for a 80/480+7887 flattener seems even cheaper than some astrographs in the markets. I cannot help but wonder how the performance of this cheap and versatile combo compare with FSQ85 and 106. Does 'you get what you pay for' really the rule here?

[社長]

Yes, and luckily I got my 7887 a long time ago which just happens to be the best one to match my 80/480.

Does 'you get what you pay for' really the rule here?

還以為David你早已把7887信託了給我，現在又要拿回來，是否趕時髦....

其實什麼才是astrograph?

- 現像你好像把問題純粹二分法：visual APO vs Astrograph。但Astrograph除了拍深空外，是否還包括拍攝月面、行星、雙星、白光、Ha或Cak太陽這類要求小視場高解像度的目標時，是軸上成像追求完美的APO好些？或是內置平場鏡、妥協了軸上成像的astrograph好些？

- 除了拍冷凍CCD時用到上萬元的PDF調焦筒那類東西外，一般公認APM鏡所用的Starlight instrument Feather Touch調焦筒是業界是兼顧目視及拍攝的最高標準，所以Astrophysics, TEC的APO折射鏡也用，好些高橋用戶也改用，那Astrograph是應用什麼調焦筒的？有沒有原厰Feather Touch電子調焦？還是買了Astrograph回來又要把本來調焦筒換成Feather Touch？

- 頂級目視APO等於保證了光軸精準，105或以上的平場鏡框也可以調光軸，我自己造的接環可以因應加或不加濾鏡而調後焦點，但內置平場鏡的Astrograph，若買回來發現像場四角星點不對稱，或僅APS片幅已在像場邊沿出現色差像差，就像買了一枝有問題的遠攝鏡一樣，可以如何調？

- 我們現時配的平場鏡，是選BORG或Sky Watcher的大通光口徑相機接環，若用濾鏡也可選M52的，以105或以上計，TMB 3.5"平場鏡的通光口徑達80mm，這次測試用的BORG 7887也是M57系統的，通光口徑大而且貼近焦平面，以減低像場失光情況(漸暈)。那Astrograph是否能做得更好？例如保證35mm全片幅角上都有100%受光，或是比遠攝鏡還要差，在中等光圈下還要在35mm全片幅的角上失光大半級光圈？要知道常見的Astrograph內置平場鏡因為遠離焦平面，較貼近物鏡，若要照顧全片幅這麼大的像場有均衡受光度，那片ED玻璃平場鏡的直徑差不多要接近物鏡大小的，那成本又要增高，所以買昂貴的Astrograph時，要肯定 you get what you pay for，抑或只是把代價付出了給近年波動的外幣匯價 (歐圓匯價比08金融海嘯時掉了約15%，澳圓或日圓匯率則持續上升)

http://finance.yahoo.com/q/bc?s=USDJPY= ... Chart&t=5y

談到 ”you get what you pay for” 這個問題，我的203APO及派拉蒙及配件總計要50萬，而你的Obsession 18UC才七萬元，所以我很有動機去認同 (僅開玩笑)....

[社長]

另外看這台鏡拍的太陽：
viewtopic.php?f=15&t=508

不知以拍太陽為優化，以Ha波段計，軸上成像優秀的的算不算Astrograph? 又或者我們再要細分平時所說的Astrogaph僅是以深空為唯一工作的Deep sky astrograph? 另外一些則是solar astrograph, lunar and planetary astrograph?

另外看這版右下側那些照片，多是用TV 0.8x平場鏡拍的，從這次測試可見，換上7887的成像只會更好，更可以照顧全片幅：
http://www.apm-telescopes.com/super-apo ... 72637.html

抑或簡單一台頂級目視APO作目視及拍攝太陽月面行星、加個平場鏡就拍深空會合理些？

[willis]

不要忘記，望遠鏡光學是一個系統工程，目鏡是另外一半故事，頂級鏡頭還是要極品目鏡配合的。那次我給你用的目鏡是TMB Aspheric Orthoscopic 25mm，相信二手價不會低於600美元。

Wow! u poisoned me with top class equipment when I was still a Lu Lu. That's why I cannot save my wallet!

也不是純Plug and play的，我的80/600跟TS2也粗略量過一下才用，當然我相信仍未優化的。

I guess the APM-LOMO 80/600 can perform better after optimization. we can do the optimization this holiday.

1. 日後若能配合魚骨版及電子調焦，比較星點大小會更客觀，這個測試我看比較像差色差很有用，但對星點解像度未能作結論，一來非無限遠的人工星點仍會引入一些球面像差，二來若沒有把焦準量化，我們不能結論出不同平場鏡的解像度高低。

The enviroment is too bright. I have used focusing mask before in a relative bright environment. We need a darker environment.

2. 抱歉我認為最後一幅圖右面 "Back Focus" 的標註有些誤導，那應該是測試時，我們加入的額外後焦距。例如TS2的5mm，應是我常用的接環額外拉長5mm，實際平場鏡框平面至焦平面應是112mm，若用單鏡反光機拍攝，機身加T Ring是標準的55mm，即接環要57mm長。以BORG 7887計，那1mm即是要在平場鏡及相機接環中加入一片1mm厚的墊片。

Oh! I am too busy in this Chinese New Yr. Someone complained this in other forum. But he didn't ask me and post my report photo! Shame! I found that 社長's post time is one day earlier than that of the guy who complained. If I could read 社長's reply earlier, I can rectified the problem. Anyway, I guess this report is very useful! Isn't it?

[willis]

Willis, 突然想起一件事，我手上還有一些Sky Watcher新出的universal flattener，不如下次把這個也測試一下

Good also try this one!

[willis]

榮耀歸 Willis

No both u & xiaoer got the honor. u share with us the flattener & the telescope. Although u went to eat, u did some of the experiment. xiaoer did the experiemnt with me.

[社長]

Wow! u poisoned me with top class equipment when I was still a Lu Lu. That's why I cannot save my wallet!

top class 不一定等於貴，又或者可以是貴買儉用。正如我推薦LVI，比我代理的另一套SBIG SG4導星器平宜一半。Sky Watcher 赤道儀可說是市面上同級帶導星口中最平宜的一類，一枝APM鏡不平宜，但郤一物多用。

我不奇怪一些新同好會以為我不斷推介貴東西，但細心比較之下便會發現我其實不斷物色最有價值的器材給大家，當然有價值的器材，往往不一定是最貴，但也許不會是最平宜的。

但有一點底線我是會堅持的：已所不用；勿薦於人。我所推薦的，都是自己在用及表現良好的器材。

天文圈內太多人，鼓動人家去買一些自己不用或用不好的器材。

I guess the APM-LOMO 80/600 can perform better after optimization. we can do the optimization this holiday.

很期待Willis盡早發表今早你我及Xiaoer的攝星報告：APM-LOMO 80/480 + TS2

我們要很高興，經過室內及星空測試後，大家都上了新一課。

2. 抱歉我認為最後一幅圖右面 "Back Focus" 的標註有些誤導...

Oh! I am too busy in this Chinese New Yr. Someone complained this in other forum. But he didn't ask me and post my report photo! Shame! I found that 社長's post time is one day earlier than that of the guy who complained. If I could read 社長's reply earlier, I can rectified the problem. Anyway, I guess this report is very useful! Isn't it?

瑕不掩瑜，世界上那份含金量高的報告是沒有打錯字的? 至少你的內文已解釋了一切。說到圖片，若你要求當事人改正他還耍頼皮的，那是無話可說了，這是一個論壇的版主應有水平嗎?

[社長]

2011-02-08 分割主題至"天文圈雜談"：
viewtopic.php?f=8&t=740

[Nebulas]

Well done.

Willis, you're very diligent, and the last picture is very special what gave us a immediate comparation.

The method is very professional and objective. We know, 事实胜于雄辩...

社长的 测距仪 是原装的吗？ 这个细节也，真是舍得投本啊！国产的可能才数百元。

[willis]

The previous test was done indoor. This time we do a field test. Most of the test was done by 社長this time. Xiaoer & I did the recording. It seems that the back focus adjustment is somewhat different from that of the indoor test. It is probably due to the difference of finite distance of the artificial star and virtually infinity of real stars. The general result is that the back focus adjustment is more in the field. We didn’t complete and fine tune all the flatteners as the sky condition and time didn’t allow. We only roughly optimized the TS2 and SW 0.85X. All the photos are unprocessed, except the resize of the original photos to 1600x1067. The TS2 flattener show good performance at the corner. The light illumination at the corner is about 79% that of the centre. This is measured by using Photoshop with a 100x100 selected area. For the field test of TS2 flattener, the target object was M42. We change to M81 & M82 because the M42 was getting to low when we stared to test the SW 0.85X. We could not complete the test for the Borg 7887. It seemed that more than 5 mm back focus adjustment is need and we don’t have thick enough spacer for that. We will come back to Borg 7887 later.

Equipment list:
APM-LOMO 80/480, Paramount (unguided), 5DII

[社長]

社长的 测距仪 是原装的吗？ 这个细节也，真是舍得投本啊！国产的可能才数百元。

原裝Leica的，1600元。

因為我經常要做工程測量，建天文台也好、天文館也好，很多東西還是用測距儀方便些。

我帶到西藏的HILTI 18mm混型土鑽咀要600多元一根，但的確好用。

[社長]

謝謝Willis整理報告，那兩天晚上我也有很多新體驗。

Borg 7887的星空表現為何跟人工星點差別那麼大，我也要研究一下，的確跟我現有知識有些出入，這點要承認。

但最值得興幸的，是APM 80/480 + TS2，有效焦距為480mm f6，又有現成的羽毛調焦，可以很強悍的。什麼時候拿去台灣拍它數個晚上，又累積多幾張漂張的深空照?

有一疑問，"The light drop at the corner is about 79% that of the centre." 其實是21%或79% ?