Starry night photos and hot pixels - help please!

[DLS]

Hi everyone. Last night I experimented for the first time with shooting star photos. When I loaded the shots into LR3 and had a look at them I noticed something a bit strange and all I could think of was "hot pixels". Is this what I'm seeing? Posted below are two consecutive shots and what I notice the most is pin points of "light" particlarly in the trees to the left of center. Flipping back and forth between thetwo shotsthe pin points move with the composition.


Anyhelp/guidance would be most appreciated. I'm a little worried that maybe its the sensor. Or is this normal?


5DII, 24-105mm @32mm.


In Custom Functions "Long exp NR" was on Auto and "High iso speed NR" was disabled.


1. 8sec, f/5.6,iso 1600


[img]/resized-image.ashx/__size/1100x733/__key/CommunityServer-Discussions-Components-Files/24/6038.Edited_2D00_6428.JPG[/img]





2. 13sec, f/5.6, iso 1600


[img]/resized-image.ashx/__size/1100x733/__key/CommunityServer-Discussions-Components-Files/24/2728.Edited_2D00_6430.JPG[/img]


Thanks in advance,


Damian

[Rocco]

completely normal. Every DSLR sensor suffers from this to some extent. I'm sure Neuro or someone like that could elaborate a bit more than me on the exact reasoning why. Probably have a dead pixel or two as well, you usually won't notice those until you do a really long exposure and those will be bright red.


A way to counter act this is to employ image stacking using software like DSS (deep sky stacker), which is free. There are some pretty good instructions to get you started in the help section. One thing you do to counter this specifically is to take "dark frames", basically taking 10-20 pictures with your settings the same and with your lens cap on right after you take your photo, while the sensor temp will be similar to what it was to take the photo.. Essentially you're taking a picture of your camera's noise. The software then uses the dark frames to subtract the noise from your "light frames".


This is a gross generalization, but that's the gist of it. If those spots don't appear with short exposures at lower ISO, I wouldn't worry at all.


p.s. Like the framing of these. you should give 20-30 second exposures a try. You'll probably find some stars in your frame you didn't even know were there. []

[DLS]

Thanks Rocco. I will try the subtraction method tonight and check out DSS as well.


I can see why this type of photography is addicting - its just simply a lot of fun sitting out under a clear sky shooting away!


Damian

[btaylor]

Yep looks completely normal to me. I generally get a couple and just clone them out afterward in lightroom or photoshop.


The first one, though almost looks like the long vertical streak of light below the

[andnowimbroke]

I

[DLS]

looks like the long vertical streak of light below the 'dot' of light is reflecting off the water... aliens?

Ha ha, not quite - car lights from the Hwy on the other side of the river.


Ya, I ended up cloning them out. Only took a minute.


Thanks for the reply.





Damian

[DLS]

Thanks ANIB, I'll check out that site.


Ya, I guess 20 or 30 bad pixels out of 9.9 million isn't too bad of a failure rate...[]


Cheers,


Damian