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-   -   Stars at night HDR-very strange image (https://forums.steves-digicams.com/hdr-98/stars-night-hdr-very-strange-image-166038/)

carylwithay Feb 11, 2010 9:48 AM

Stars at night HDR-very strange image
 
1 Attachment(s)
Here it is:
Caryl

Wonger Feb 11, 2010 9:56 AM

looks like pins trying to poke through

maggo85 Feb 11, 2010 4:45 PM

Now this looks crazy... can you tell us how you've created that one?

carylwithay Feb 11, 2010 5:01 PM

Well, I remember some of it. I took 3 timed shots of the sstars and put them into PhotoMatix. Then I played within PSCS4 but I did so many things and erasures than I have no idea how this happened. It looks like embossed metal to me.
Caryl

Bynx Feb 11, 2010 8:52 PM

Wow I thought thats exactly what it was .... embossed metal. But now its really interesting if its an HDR alteration from actual stars. Nice one. Really weird though.

mtngal Feb 11, 2010 11:38 PM

Definitely strange. What exposure settings did you use? And was there a light somewhere to the right? The strange effect seems to be stronger on that side, and it looks like there's additional light on that side of the frame.

carylwithay Feb 12, 2010 12:06 AM

I was on bulb and did 20 sec,30 sec and about a min with a 12mmlens on the M8. f/8. Does that help?
There was no light on the right since it was about 1AM.
Caryl

VTphotog Feb 12, 2010 12:36 AM

The brighter area from the upper right diagonally to the lower center, looks about right for the Milky Way, depending on how your camera was oriented. I think that some of the effect may be from the alignment done by Photomatix. The rest may be from some noise reduction.
For these kinds of shots, you should do a dark frame subtraction to cancel out the hot pixels before putting them together. Just take a shot with the lens cap on for about the same exposure time as you are using. Quite a bit of what look like stars can turn out to be hot pixels on the camera sensot itself.

brian

carylwithay Feb 12, 2010 1:22 AM

thank you Brian. I will do that.
Caryl

MartinSykes Feb 12, 2010 6:00 AM

Maybe Photomatix is creating a bit of a halo round each star which when combined gives you the effect you see.

Also, the Earth is rotating (360 degrees a day obviously) so on a 1-minute exposure the Earth has rotated a quarter of a degree. The sky will therefore rotate quarter of a degree around the pole star. If that's somewhere in the top left, those stars will have stayed relatively still and the bottom right will have moved more.

I think you can get tracking tripods to correct for that if you're doing a lot of long exposures at night.


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