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FORUMS Photo Sharing & Visual Enjoyment Astronomy & Celestial 
Thread started 08 Jul 2012 (Sunday) 11:22
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Astronomy and Celestial NOOB has questions.

 
ChrisMc73
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Jul 08, 2012 11:22 |  #1

Hi, I'm a total noob when it comes to taking photos at night, of the stars or anything that requires long exposures due to little to no light, such as stars.

I decided to go out into my back yard and snap a few test shots to play with some settings. I realize the back yard in suburbia isn't an ideal place to try to get the stars, but I just wanted to see what I could come up with. I didn't really know what to use for my settings, it became pretty clear to me quickly that having the lens in AF mode wasn't going to work. I guess you all know this, but I didn't, lol, told you total NOOB.

Anyway my first test shots were of just my house using long exposures to see if I could get enough light from the neighbors back porch lights, to see my house. It worked, but there seem to be a lot of little spots in my shot, and thats the first thing I want to ask here. What are these spots caused from, is it good, bad, camera malfunction etc?

I was using my 5D Mark II and 24-70 lens.

Here is the photo you can see all the EXIF information with it...
http://www.flickr.com …/in/photostream​/lightbox/ (external link)

I later pointed at the most stars in the sky I could see with my naked eye and dorked with the settings and got these two shots...can't tell if those same spots are in it or not, as its mostly a starlit sky...

http://www.flickr.com …528268934/in/ph​otostream/ (external link)

http://www.flickr.com …528270574/in/ph​otostream/ (external link)

So really I am just curious what all the "firefly" type spots are in that first link, if its correctible or if its a defect in my camera?




  
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HaroldC3
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Jul 08, 2012 11:44 |  #2

The "spots" are called hot pixels (http://en.wikipedia.or​g …_pixel#Bright_d​ot_defects (external link)), they are normal for long exposures. You can use dark frame subtraction to remove them (http://en.wikipedia.or​g/wiki/Dark-frame_subtraction (external link)).

For your sky shots, try ISO 3200, 30s and f2.8 and see if you can get more stars pictured. It will be pretty hard though because of the light pollution. You may be able to get an image of the Milky Way galaxy though. That's a popular subject for people shooting stars.


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ChrisMc73
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Jul 08, 2012 12:02 |  #3

Thanks Harold. I knew there was a name for those spots! I appreciate your info here.




  
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ChrisMc73
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Jul 08, 2012 13:42 |  #4

HaroldC3 wrote in post #14687571 (external link)
The "spots" are called hot pixels (http://en.wikipedia.or​g …_pixel#Bright_d​ot_defects (external link)), they are normal for long exposures. You can use dark frame subtraction to remove them (http://en.wikipedia.or​g/wiki/Dark-frame_subtraction (external link)).

For your sky shots, try ISO 3200, 30s and f2.8 and see if you can get more stars pictured. It will be pretty hard though because of the light pollution. You may be able to get an image of the Milky Way galaxy though. That's a popular subject for people shooting stars.

So even though hot pixels are normal for long exposures, this many seems pretty alarming to me, but maybe its because I'm not an expert. Do most high end cameras experience this in the same situation?




  
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dougj7
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Jul 08, 2012 14:02 |  #5

ChrisMc73 wrote in post #14687948 (external link)
So even though hot pixels are normal for long exposures, this many seems pretty alarming to me, but maybe its because I'm not an expert. Do most high end cameras experience this in the same situation?

Yes, all cameras will have hot pixels during long exposures due to heat build up on the sensor. That's why most dedicated astrophotography cameras will have some sort of cooling. Usually thermoelectric cooling (TEC).




  
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ChrisMc73
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Jul 08, 2012 14:27 |  #6

Oh ok, I see. That makes sense. Ok, tonight I'll try the new exposure tips and see how it goes.
Let me ask you all this...when setting up the image, framing it, its hard to see anything in the view finder or live view, how do you know how or where to focus so that you get the stars in focus? Since I had to set it into MF I didn't quite know where to focus, I was just turning and praying etc...how do you do that for those kinds of shots, especially if you can't see much when in the city?

I would guess if I were doing say a night city scene, I'd just try to focus on something that had any light at all in the frame of where I wanted the shot and subject, but with stars its a lot different.




  
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dougj7
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Jul 08, 2012 14:37 as a reply to  @ ChrisMc73's post |  #7

stars will be in focus at infinity. the problem is that most lenses will focus past infinity, so it becomes a guessing game. try the program in the link below. it uses a focus method called FWHM.

http://www.ideiki.com/​astro/ (external link)




  
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ChrisMc73
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Jul 09, 2012 06:56 |  #8

HaroldC3 wrote in post #14687571 (external link)
The "spots" are called hot pixels (http://en.wikipedia.or​g …_pixel#Bright_d​ot_defects (external link)), they are normal for long exposures. You can use dark frame subtraction to remove them (http://en.wikipedia.or​g/wiki/Dark-frame_subtraction (external link)).

For your sky shots, try ISO 3200, 30s and f2.8 and see if you can get more stars pictured. It will be pretty hard though because of the light pollution. You may be able to get an image of the Milky Way galaxy though. That's a popular subject for people shooting stars.

I tried these settings last night, no luck, too much light pollution from the suburbia.
I guess most folks get away and out into the country away from city lights when they capture the really good stuff? If only this dad of a 1 and 3 year old could do that one day...




  
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archer1960
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Jul 09, 2012 18:16 |  #9

ChrisMc73 wrote in post #14688105 (external link)
Oh ok, I see. That makes sense. Ok, tonight I'll try the new exposure tips and see how it goes.
Let me ask you all this...when setting up the image, framing it, its hard to see anything in the view finder or live view, how do you know how or where to focus so that you get the stars in focus? Since I had to set it into MF I didn't quite know where to focus, I was just turning and praying etc...how do you do that for those kinds of shots, especially if you can't see much when in the city?

I would guess if I were doing say a night city scene, I'd just try to focus on something that had any light at all in the frame of where I wanted the shot and subject, but with stars its a lot different.

Move the camera to something in the sky that IS bright enough to see, and focus on it. Then move to your subject. Just like focusing and recomposing something on the ground.


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spotz04
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Jul 09, 2012 22:57 |  #10

ChrisMc73 wrote in post #14687948 (external link)
So even though hot pixels are normal for long exposures, this many seems pretty alarming to me, but maybe its because I'm not an expert. Do most high end cameras experience this in the same situation?

Yep. My 5DII gets them, as does my other two EOS bodies. Pretty typical as the sensor heats up during long exposures. The more long exposures you do the more hot pixels show up.

You can attempt to remap the sensor. Remove lens, attach the body cap, then put camera in Manual Clean mode (in the camera's menu). The mirror will flip up, leave in this mode for about 30 to 60 seconds and DO NOT remove the body cap. After 30 to 60'ish seconds turn power off on the camera - you'll hear the mirror drop down again. If hot ones don't go away after doing this then run it again. I run my bodies through this after doing long exposures as to minimize the issue for the next time I shoot long exposure.

What I do with my 5D2 and 24-70 is zoom out to 24mm, find a star or group of stars in the viewfinder and try to get a good focus while focus ring is near Infinity. Near, as in, slight backed off Infinity. Then switch on Live View and hit the zoom button (on upper right on back of camera body) a couple times until you're at 10x in the LCD screen. Now manually focus to get an even sharper focus on the stars. I'm a Noob at this too and find focusing this way works best for me.




  
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ChrisMc73
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Jul 10, 2012 09:39 |  #11

Thanks guys, I'll give these suggestions a shot this week. Its hard to find time to get out under the stars with a 1 and 3 year old, lol...but I'm not giving up.




  
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nburwell
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Jul 11, 2012 12:38 |  #12

I think the most important thing, as it has already been stated here, is to get away from the light pollution. I know it can be hard getting away being a father and all. But you have the right equipment to photograph the stars. Maybe if you're able to scout out a place beforehand and get away for a night (make sure it's a clear night) you could probably capture way more stars and even the Milky Way.

I'm a noob at astrophotography as well, but I'm just learning as I go along.

Best of luck!

-Nick




  
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ChrisMc73
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Jul 13, 2012 00:15 |  #13

Thanks Nick, I'm hoping to get away soon. Need to scout some locations.




  
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