|
|
Post by markt on Jul 20, 2008 15:53:51 GMT
As you're all no doubt aware we had a really good display of NLC on the evening of the 15th July. Quite a few of us saw it and there are also quite a few photos taken at the same time from different parts of the country. I thought it would be an interesting project to group these chronologically and then sort the respective groups by location - the most northerly at the top of the group, the most southerly at the bottom. This way it should be reasonably easy to see the effects of parallax of observing the same NLC features from different geographical locations. 21.40ut west mids  selsey 21.42ut west mids  wales  selsey 21.47ut anglesey  west mids  wales  selsey 21.51ut west midlands  Hampshire 21.56ut anglesey  west mids  wales  hampshire  selsey 22.25ut glengarnock  anglesey Ok, I think that's pretty much all the images we have so far. If anyone has anymore they can add to this then please let me know. In the mean time what do people think? I think it's turned out pretty ok. It's interesting to see the display get progressively closer to the horizon the further south it was observed. There also seems to be some vertical compression visible the further south the display was observed. For a given time the same structures are visible in all of their respective 'group' of photos, though with people photographing at different focal lengths it can sometimes take a bit of locating due to the shift in image scale. Enjoy  |
|
|
|
Post by tmcewan on Jul 20, 2008 16:54:23 GMT
Great work Mark, much appreciated.
Tom
|
|
|
|
Post by markwalters on Jul 20, 2008 22:13:22 GMT
Excellent review of the days observations, thanks Mark
|
|
|
|
Post by Jay on Jul 21, 2008 17:46:09 GMT
Interesting, i really need a better camera, because i noticed some of the pics taken at the same time show details that i didnt pick up with my camera, im guessing the decent pics are all done with a digital slr, so i cant really complain as mine is a relatively cheap and simple digital camera (canon powershot A630) i think its a ok camera for the price, and the price suited my budget so i will have to make do with it for the time being!
Please can someone explain exactly what parallax actually means?
|
|
|
|
Post by Jay on Jul 21, 2008 20:05:48 GMT
Thanks, that was clear enough!
|
|
|
|
Post by markt on Jul 21, 2008 20:21:07 GMT
Interesting, i really need a better camera, because i noticed some of the pics taken at the same time show details that i didnt pick up with my camera, im guessing the decent pics are all done with a digital slr, so i cant really complain as mine is a relatively cheap and simple digital camera (canon powershot A630) i think its a ok camera for the price, and the price suited my budget so i will have to make do with it for the time being! I think, looking at your pics, they're exposed for the brightly lit buildings in the foreground rather than the NLC and sky in the background - the NLC look slightly underexposed to me, thats all. Were you doing an auto exposure, letting the camera decide, or did you plug in a manual exposure? |
|
|
|
Post by Jay on Jul 21, 2008 22:51:01 GMT
I had it set on manual, the settings for the 21:51 pic were focal length 10.84mm, F number 4/5, exposure time 3.5 seconds, ISO 200, metering mode center weighted average exposure compensation 0 step (I have to admit the only thing i understand in that is the exposure and the ISO i remebered from my old SLR that if it was dark i needed a longer exposure time) i can have maximum of 15 seconds with my camera i have now, but i think 15 seconds would be over exposed? i also knew about ISO, i used to use 400 iso film for my slr for astrophotos, but i knew that the higher the iso the more the picture appears grainy, so i decided to use a lower iso for my nlc pics for less grainy pics (i still think they look a bit grainy though!)
the 22:26 pic was 4 second exposure time.
Sorry if this is difficult to understand!
|
|
|
|
Post by Jay on Jul 21, 2008 23:00:47 GMT
also, just noticed the second pic i took was at 21.55 and it is with the 21.56 pics, i know its only a 1 minute difference but i guess in science 1 minute is a lot, however the exact time was 21.55 and 56 seconds so only a few seconds out really (i did say it was 21.55 in the early warning section)
|
|
|
|
Post by Jay on Jul 22, 2008 7:31:30 GMT
Hopefully I will have more chances to experiment soon!
|
|
|
|
Post by markt on Jul 22, 2008 7:57:00 GMT
Hopefully I will have more chances to experiment soon! Yes, hopefully  Given similar observing conditions i'd go for (assuming same other settings) an exposure of around 5 seconds. I suspect the foreground buildings would be over exposed and washed out on 5secs, but heck, that don't matter cos' it's not those you're photographing! To try and hide this from the eye you could aim the camera higher in the sky so there's less overexposed buildings in shot. If you look at the last picture I took in this sequence nlcnet.proboards77.com/index.cgi?board=2008&action=display&thread=221 the 22.59ut pic - the foreground here is overexposed (lovely light pollution!) whereas the backround isn't quite as exposed as I would like, it also has that 'grainy' look that you describe in your pic. Still p[ractice makes perfect, and I think it's safe to say we're all still experimenting and learning as our NLC photography goes on |
|
