www.astrocafe.hk

Some old deepsky photos I've acquired late november last year. I wasn't able to deal with the uneven background probably because I haven't taken flatfields.

Images below are taken at Tin Hau, HK Island, roof-top of my building.

60sex x 60, Sky90, EM11, unguided, 40D modified.

Wooow, thanks Paul for sharing, I lived in Tin Hau before and one can image how is the light pollution there at the centre of city. Your photo clearly illustrate we can still do something nice through reasonable preparation.

I owned Sky 90 before and now have 40D on hand. Would you share a bit more,

- field flattener is used?
- what kind of light pollution filter, if any, used?

My guess is, in some very clear nights at Tin Hau, with ISO400 and LPS filter, at medium aperture, you can still extend the exposure time up to 10min or so before the photo is being washed out, is it?

I used the Tak flattener@F4.5 for the images, and IDAS LPS.

I remember using ISO1000 for these images. When I first started trying imaging at rooftop I tried ISO400 2 years ago, but I couldn't get anything useful over 2.5 min.

At that time I was using 350D and there were some banding noise issues which i suspect was due to incorrect dark frames and read-out noise due to low ISO settings. So, I won't do anything under ISO800 when shooting here.

Thanks for nice sharing! What processing software u are using?

DSS, Photoshop, PixInsight LE, IRIS

PaulNg 寫:I used the Tak flattener@F4.5 for the images, and IDAS LPS.

I remember using ISO1000 for these images. When I first started trying imaging at rooftop I tried ISO400 2 years ago, but I couldn't get anything useful over 2.5 min.

At that time I was using 350D and there were some banding noise issues which i suspect was due to incorrect dark frames and read-out noise due to low ISO settings. So, I won't do anything under ISO800 when shooting here.

yes, so that's close to what I guess, as here in Sheung Shui, I am shooting at f6 at ISO800, LPS is ok for me to exposure up to 10mins, the sky background at Tin Hau is a bit brighter, so that's f4.5 at ISO1000 for 2.5min.

Over the last decade I don't involve in astrophotography very much, more focus on hardware stuffs. Now it's the time for me to pick again, and learn more from all of you on camera and post processing stuffs.

Feel free to share more

WIth iso1000 i couldn't get anything longer than 1.5min
ISO400 is better at around 2.5min.

I took these shot after midnight to avoid the most light pollution, but still this is a really bad situation.

Dear Paul,
Can u give some general rules that how one select ISO in DSI in light polluted area?
Regards,
Willis

PaulNg 寫:WIth iso1000 i couldn't get anything longer than 1.5min
ISO400 is better at around 2.5min.

I took these shot after midnight to avoid the most light pollution, but still this is a really bad situation.

understand, may be a 30min drive to Shei O will make a lot difference.

willis 寫:Dear Paul,
Can u give some general rules that how one select ISO in DSI in light polluted area?
Regards,
Willis

From my experience, it is a good idea to one or 2 stops below the highest ISO possible, and in combination with the exposure time to prevent over exposure of some bright objects (like core of M42).

M45，单张1分钟，60张叠加，累计有1个小时的曝光了。但信噪比还是差些。
单张的时间还是太短。在香港拍深空，光害还是很制约。
上次去香港的时候，坐船去参观过大佛像，那边小渔村的光害是不是好些呢？