Posted by Rylan Schoen on August 6, 2008 at 6:26 PM
I took this last night up near the Mt. Baker Ski Area. Not a great picture, but my fist attempt at something like this. Looks like i captured some of the northern lights also. I have some concerns about eh purple though. i'm pretty sure that it's light coming in where it is not supposed to, but i am unsure if its a camera thing or my lens. does anyone have suggestions on what i should do to fix this. Thanks a bunch!
Hi Rylan, what might be happening here is light from behind the camera is leaking in via the viewfinder. Some cameras have a slider to block that - some do not. If yours does not you can put something black and thick over the viewfinder during the exposure.
That's all I can think of right now. Anything else is expensive....faulty camera???
Did you have a flashlight going behind the camera? Maybe shined it on the back of the camera a time or two......??
Posted by Bryan Spahr on August 6, 2008 at 6:58 PM
Hey Rylan,
I'm not entirely sure but I have heard accounts where these "spots" appear due to the sensor reacting to heat from the camera battery. It would seem to me that this would require a fairly long bulb exposure like the one you have here for this to be even plausible. Not necessarily the only explanation but something to think about.
Posted by Curtis Knight on August 6, 2008 at 7:19 PM
I agree with Rick. It looks like some kind of light leakage, whatever the source. Looks a lot like the spots I used to get when processing slides and something wasn't sealed properly or the black bag didn't get zipped shut all the way, etc...
Posted by Darren White on August 6, 2008 at 7:45 PM
The same thing happened to me with my D70....its the sensor heating up...
the d300 does not do that!
Posted by Rylan Schoen on August 6, 2008 at 9:41 PM
thanks for the quick input. I do have one of those sliders, but i did not have it with me. It is also very possible that my headlamp flashed through the viewfinder when i was coming back to find the camera.
if it is a heat problem; would one of those external double battery holder packs help? like this one: http://www.amazon.com/Nikon-MB-D80-Multi-Power-Battery-Digital/dp/B000HJ5N2Y
Posted by Sean Watson on August 7, 2008 at 1:48 PM
I haven't tried any 20+ minute exposures, but this was pretty bad on by D100 and I stopped noticing it on my D2x. I agree it's probably heat. If you want to test it, take a long exposure with the lenscap on in a dark room (try covering the eyepiece).
You might try stacking a bunch of shorter-exposure images (104 15s exposures). I hear that also helps with noise. I know there is software to help with that, but I don't have the details.
I wonder if you could kill the purple in the channel mixer.
Sean
Posted by Mike Stovall on August 7, 2008 at 2:21 PM
Drop the ISO down to 200 or 400. Think of ISO kind of like gain on an audio amplifier. Lower sensitivities should use less power, generating less heat. You should be able to shoot with the aperture wide open with the focus on infinity to keep the exposure level the same.
According to DOFMASTER http://www.dofmaster.com/dofjs.html, at F/4 and 26mm, everything is in sharp focus from 28 feet to infinity (when focusing at infinity).
I read somewhere that the sensors on telescopes at observatories are cooled with liquid nitrogen or something similar to cut down on noise.
You could try feeling the battery after shooting a long exposure to determine if it contributes a lot of heat near the sensor, but I'd bet you are getting heat from components near the sensor or maybe the sensor itself.
Its sensor heat for sure. It's a common problem with astro photography. There are photoshop actions out there that remove this. It usually involoves taking a "light" frame like the one you have and a "dark" frame with a lens cap on. The action compares the two frames and removes the duplicate light or glow that is caused by sensor heat. You can get much information about this on the astronomy forums like cloudynights.com.
I will dig around on some information that I have. I have read that if you set the shutter to continuous shooting and pick like 15s or 30s you can use a cable lock to take all of the exposures in an interval until you fill a card or have enough exposures to calculate the time you originally would have kept the shutter open. There is a photoshop action that I read about on another forum that will allow you to combine the different exposures and it does 2 images at a time so it doesn't eat up memory or keep pounding on the cpu.
I haven't been able to get far enough away from the city to experiment with star trails yet, but if anyone knows some good locations somewhat near the Portland area that would be awesome.
Discussion
9 repliesNikon D80 19-34 @26mm
iso-1250 f/11 1575 (approx 26 min)
That's all I can think of right now. Anything else is expensive....faulty camera???
Did you have a flashlight going behind the camera? Maybe shined it on the back of the camera a time or two......??
I'm not entirely sure but I have heard accounts where these "spots" appear due to the sensor reacting to heat from the camera battery. It would seem to me that this would require a fairly long bulb exposure like the one you have here for this to be even plausible. Not necessarily the only explanation but something to think about.
the d300 does not do that!
if it is a heat problem; would one of those external double battery holder packs help? like this one: http://www.amazon.com/Nikon-MB-D80-Multi-Power-Battery-Digital/dp/B000HJ5N2Y
You might try stacking a bunch of shorter-exposure images (104 15s exposures). I hear that also helps with noise. I know there is software to help with that, but I don't have the details.
I wonder if you could kill the purple in the channel mixer.
Sean
According to DOFMASTER http://www.dofmaster.com/dofjs.html, at F/4 and 26mm, everything is in sharp focus from 28 feet to infinity (when focusing at infinity).
I read somewhere that the sensors on telescopes at observatories are cooled with liquid nitrogen or something similar to cut down on noise.
You could try feeling the battery after shooting a long exposure to determine if it contributes a lot of heat near the sensor, but I'd bet you are getting heat from components near the sensor or maybe the sensor itself.
I haven't been able to get far enough away from the city to experiment with star trails yet, but if anyone knows some good locations somewhat near the Portland area that would be awesome.