In search of partner, flattener, for APM-LOMO 80/600

[willis]

The same game of APM-LOMO 80/480 was done for the APM-LOMO 80/600 by xiaoer & I. Before the flattener test, we first do the star test. Again this is an indoor test. Due to the finite distance of the artificial star, we would expect some differences in back focus adjustment in the case of field test. But the result is a good reference. For the experimental detail, one can refer to:
viewtopic.php?f=21&t=724

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 80/600. This result supporting that APM-LOMO 80/600 can be an excellent astrograph. We will perform the field test later.

(**The data for TS 2 is not back focus adjustment, but back focus)

Special thanks 社長 for lending as the equipment!

[社長]

Thanks Willis for the nice report!

有少許疑問，Astro Tech 的中央及角上星像是否對調了? 否則我認為中央的星點調焦不準。這個沒問題的，不時做統計時也要把存疑的數據刪去。

唯一是除Televue外，每一個平場鏡的表現好不錯? 哪星空測試夠煩了

若有興趣，我可以用台APO建立一個平行光管，然後製造一個無限遠人工星點作為測試光源，下圖中那個projection lens，Markus Ludes是用高橋Hi Or 2.8mm目鏡做的：

http://aberrator.astronomy.net/scopetest/

[willis]

Yes! I guess the AT case was not properly focused. We didn't use focusing mask and only judged the focus by using the camera's tiny display, there would be error. I guess we need to further experiment the flatteners in the field. The problem this time is that we got lots of potential match flatteners. BTW, there are some more photos, including ur beloved Brookie. He was a stupid cop that day. He pushed the tripod of the artificial star. Am I spell it right?

[Nebulas]

每次你总喜欢把它弄出来，哎，这只猫也真够有表演天分的！

[社長]

全名是Oogie Boogie man，在怪誕城之夜，受萬聖節市長指派去綁架聖誕老人回來的，因為他們想辦搞聖誕節。

我的貓女通常叫Towser，全球唯一被立銅像的貓，破了世界紀錄抓得最多老鼠：

http://www.purr-n-fur.org.uk/famous/towser.html

[popkrab]

Hello,

My name is Pornchai POP from Bangkok, Thailand. I also have a APM LOMO 80/600 in WO tube. I also ha field flattener, WO 0.8X first version which designed for WO red tube aniversary. I found the best result for 80/600 is #7887. TVRF 2008 is not matched for this scope. Also AT2F is good but not good enough due to astigmatism at outer 60% of frame of 42mm. image circle tested by EOS 5D with real star in the sky.

I would like to say thank you very much for your tested and review. The result confirmed my result.

Can you let me effective focal length of APM LOMO 80/480 if use with BORG #7887? Because when I use 80/600 couple with BORG #7887 with 55 mm. back focus distance, it was 536 mm. focal length. This number calculated by using Plate-solved method in MaximDL. I calculated back to magnification factor of this BORG is 0.89X , not 0.85X as advertised.

For this reason, I'm not sure if I use BORG with APM 80/480.

Thank you very much.
POP

[willis]

Dear Pop,
Welcome to astrocafe! Recently we find that the back focus adjusment in indoor (finite distance) and realy sky (infinity distance) is different. We are working on all the back focus adjustments in realy sky condition. Once it is done, we will post it. Tranditionally, most APM-LOMO 80/480 & 80/600 people use TV 0.8x, which is suggested by APM. However, we find there is possibility that other flatteners work. BTW, do u fit any spacers in ur 7887 for APM 80/600. There are two locations in 7887 that one can fit spacers.
About the magnification of the flatteners, I didn't test the effective focal length of the flattener. ur suggestion is good. I will try to fo it later.
Regards,
Willis