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Photography Question 
BetterPhoto Member Since: 2/7/2005

Star Trails shot

Hi All

Over the past few nights, I have attempted and failed to do Star Trail shots. The first few times, my battery actually died before the shot was finished (I was hoping for a 2 hour exposure). Second time, I kept watching it until battery power was down to minimal then turned it off (about 1.5 hours), but then nothing, my poor camera was overworked I think. I just kept getting a busy flashing signal for hours afterward, and no photo.

Has anyone else had this issue with digital, is it something I should just be doing with film?

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5/28/2006 8:00:24 PM

BetterPhoto Member Since: 12/6/2004
  Hmmm, I've heard it is much better with film but I haven't had time to try it with film nor digital so I don't know for sure .... it is just what I've heard.

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5/28/2006 8:23:39 PM

Peter M. Wilcox
BetterPhoto Member Since: 5/30/2005
  Digital sensors in non-astrographic cameras aren't designed for exposures longer than a minute or so. The sensor heats up, the pixels self expose, noise levels increase, etc...

Astrographic sensors have electronic coolers to drop the temperature way down and allow long exposure.

This is one area in which film still works better, although you will get reciprocity failure in film, and need to compensate for it.

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5/29/2006 9:00:14 AM

Spencer Doyle
BetterPhoto Member Since: 2/10/2006
  Natalie, I'm not sure which digital camera you're using. That being said, I'll explain why you would get the "busy" signal from a Canon 20D, but it may or may not apply to your camera. If I were to take a 2 hour exposure with the 20D, it immediately takes another 2 hour exposure after the first one is complete. What your camera is doing is another identical exposure in an attempt to eliminate dead pixels so your final image is much sharper.

One thing I'm not clear on is what affects that 2nd exposure. For example, if I were to throw the lens cap on it, put it in the car & drive home....I don't know if it would still eliminate the dead pixels or not. Can anybody else answer this?

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5/29/2006 3:21:04 PM

BetterPhoto Member Since: 2/7/2005
  Thanks guys, I don't think I am going to attempt it again on digital, I don't want to stuff my camera. I can easily do it on film, but as it is a Tafe (Junior Collage) assignment and I am restricted by time. I don't want to waste a whole roll of film on a couple of shots then spend time hand processing everything as I don't think I will get it in on time. Teacher said this shot was "optional", so I suppose I will opt to not do it until I need to use some B&W film in the near future, then I'll give it ago.

Yes just leart about the law of reciprocity failure!

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5/29/2006 4:22:55 PM

Stephen J. Innes  
Hello friends.. I was wondering the same thing fairly recently when considering a few longish exposures, hope-for-the-best. If it's any help I have the 20D and the battery grip with the remote switch - so I gave a full charge to the 2 batteries you fit in the grip and took the camera outside when in the depths of winter, aimed at the pole star and with the 10-22mm at 10mm on f5.6 on my ancient Manfrotto 055 I left it recording a star trail, then went indoors for a heat and a tea! I left it out there for about I think 50 minutes roughly.

I believe the 20D on veeeeery long exposures automatically applies dark frame subtraction. What that means, as Spencer D confirms, is after the initial exposure is terminated, another begins but does so electronically - in my limited experience you can leave the lens cap off and it won't matter. All you need is the battery power to allow for your actual photograph, then sit there chewing fingernails while the the dark frame subtraction gets to the end of its job, removes hot-spot pixels and bingo-with luck, a star trail.

The problem with long exposures is you need as little light pollution as possible and a looooong night. That means it can get cold out there. So the battery gets affected. I've heard some folks wrap their cameras in bubble wrap to keep the warmth in! Maybe by putting the battery in your pocket until you've set the picture up and then firing up the exposure, you'll get somewhere.

If it's of any use I append the only two really okay ones I ever got on the 20D with battery grip and two fully-charged batteries. A third one is spooky ish and I might add it later - it got slightly ghostly due to a 1hr 10 exposure at the bottom of a field near my house; but it was so cold down there the 20D iced up - so did the lens, front element and all. Worked fine though, phew. Camera still going strong.

I had to Photoshop the worst of the light pollution away but what I ended up with was what had been there in the image all along.. any thoughts, please let me know! All the best. S.

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5/31/2006 5:09:08 PM

Stephen J. Innes   Whoops.. not too good at uploading.. whatever - I shoved them in the mini gallery which I haven't added to in ages.. if anyone is interested have a peek in there. I'll get the hang of this attach-pictures thing one day.. maybe. All the best again. And I'm going to give the star trails more of a try when the sky is clear and wintry enough here in Ayrshire, Scotland.


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5/31/2006 5:13:47 PM

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