I was trying some long exposures the other night in my backyard to practice the technique as I plan on driving about 20 miles out of town to get some star trail pictures soon. I had long exposure noise reduction turned on and noticed it took the same time as the original exposure to finish processing, so a 30 minute exposure took another 30 minutes to process. This brings up a question as I will be snowshoeing near the Cascade Mountains when I take my star trail picture(s).
If I take a one hour exposure on the bulb setting, will I be able to move the camera and put on the lens cap while it is taking another hour to do the long exposure noise reduction. I would rather head back to my car instead of waiting another hour in the snow until it finishes if possible. If this is not possible, is there something I can do in post processing that will take the place of using long exposure noise reduction in camera? I am using Lightroom 4 for my post processing. Thanks.
Yes, you can put the lens cap back on and take the camera back to the car while the NR is processing. Just don’t turn off the camera. Also make sure that you start off with a full battery – the battery will drain faster in the cold than normal.
If the car is warm when you go back, you may want to put the camera in a plastic bag before getting in the car to avoid condensation.
Thanks for the response Dave. It is good to know that I don't have to stand out in the snow for an extra hour while the camera processes the noise reduction. Also, I will definitely use a plastic baggie to try to avoid condensation when I put my camera in my car. Now I've just got to wait for a nice clear sky in the near future.
What I'm thinking of doing for this shoot is scrubbing the one long exposure and instead taking about 90 minutes worth of 30 second exposures and then stacking them in a free Startrails program I downloaded. This will ensure that if something goes wrong at some point (dead battery etc.)during the shoot, I will at least have however many exposures I have taken up until that point. I will leave on the Long Exposure Noise reduction so each 30 second exposure should take about a minute for both exposure and noise reduction to process.
It also means if I need to leave after an hour, I will at least have an hours worth of exposures complete
Does anyone have any input as to other advantages or disadvantages to stacking multiple exposures as opposed to one long exposure. One thing I will have to test is how well the mountains in the foreground will be exposed with only 30 second exposures, as I want them to be a feature. I don't think my flashlight is powerful enough to light them
That's a good point. I'm not sure about having gaps if there is 30 seconds between exposures. I will have to do some research. I know that using stacked images is a common method for photographing star trails, I'm just not sure if people use noise reduction when using that method.
Any gap between exposures beyond a few seconds will show gaps in the startrails. Skip the long exposure noise reduction and shoot a dark frame to use with the Startrails program. That will eliminate noise very effectively.
Concerning use of long exposure noise reduction, yes you can put a lens cap on the camera and move it while it is shooting the dark frame. But, you must keep the camera in a like temperature environment while it is doing it. If you move it to a warmer environment it changes the sensor noise patterns and will be ineffective.
Tom From Beautiful Smith Mountain Lake in Virginia
Thanks for the advice on using the dark frame technique. I see that my star trails stacking program allows me to insert a dark frame. Please excuse my lack of knowledge on the subject, but how do you properly shoot a dark frame. Do you simply take a picture with the lens cap on, and if so, do you use the same exposure setting and exposure time as your other star trail shots. i.e. does does the dark frame have to be a 30 second exposure if the other shots are 30 second exposures? Thanks.
Sat 15-Dec-12 12:24 AM | edited Sat 15-Dec-12 12:25 AM by tcerul
Same exposure settings as used for star trail shots should be used for the dark frame. If you used 30 second exposures then 30 seconds for the dark frame. And yes, just take another picture with the lens cap on and insert that photo into the dark frame area in the program.
Tom From Beautiful Smith Mountain Lake in Virginia
Will you also be using high ISOs? If so, you may be back to square one with noise. In that case,you might also have to use High ISO NR. However, I'm not sure if LE NR and High ISO NR play well together.
Of course, you could lower your ISO considerably, but that would substantial exposure time, and much longer LE NR processing time as a result.
High ISO NR is a traditional noise reduction technique that looks for random pixels. Long Exposure Noise Reduction is a dark frame subtraction method and is entirely unrelated.
Regarding dark frame subtraction, here's a sample file that illustrates what we're trying to avoid:
The pinkish stuff along the right hand side of the frame is thermal noise, and it's not supposed to be there. This particular frame is from a D2h at 30 seconds, perhaps more pertinently at about 15F - from my LR record it's clearly apparent that we were at this location for at least two hours before this shot, and I certainly remember being cold.
If I had been using LENR, the second exposure would have been with the shutter closed (that's why putting the lens cap on has no effect!) and the resulting frame should in theory have been all black. But it wouldn't be, since all this pink stuff would have been in it. So the camera can then compute that anything not black shouldn't have been in the previous frame, and it can remove it. Attachment#1 (jpg file)
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