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long exposure for astronomy (or what ever)
went out last night with the astronomers, and i thought i can make
pictures... so you can set the d70 to 30 sec. that's it? what if i want to make an 1 hour exposure? I found out that when i set the d70 to bulb, i can start it with the remote and turn it off with the remote. but it stays only open for about 30min. and then it takes another 30 min before i can touch it again. with any film slr you could do that easy, is this where we meet the limit? i also noticed, that this is very hard on the batteries. normally i don't have to charge them for 1000's of images, and with long exposure i can make 2-3 images and the battery is flat. cheers |
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"Dimitri" wrote in message m... went out last night with the astronomers, and i thought i can make pictures... so you can set the d70 to 30 sec. that's it? what if i want to make an 1 hour exposure? I found out that when i set the d70 to bulb, i can start it with the remote and turn it off with the remote. but it stays only open for about 30min. and then it takes another 30 min before i can touch it again. I'm not sure why it stops at 30 minutes... That second 30 minutes is a dark frame subtraction (Mode 2). Go to Mode 1 instead. Or, better yet, simply power the camera off after the shutter closes (right at the end of the first 30 minutes). At that point, the camera has saved a truly raw image, with no despeckling or dark frame subtraction, which will be surprisingly sharp. Then turn the camera on and take the next one. Take *one* dark frame this way, manually, and subtract it using software. Disclaimer: This is what I've been told about the D70. I have not yet used one. with any film slr you could do that easy, is this where we meet the limit? To make a 1-hour exposure, you should take 10 6-minute exposures and add them. This results in far less noise than a single 1-hour exposure. For some techniques to do the adding with Photoshop, see www.covingtoninnovations.com/dslr. You can use software like Images Plus, which is specifically for astronomy, to do it more conveniently. i also noticed, that this is very hard on the batteries. normally i don't have to charge them for 1000's of images, and with long exposure i can make 2-3 images and the battery is flat. You should be able to go a couple of hours with one battery charge. I always bring a spare battery with me. I don't know about Nikon, but Canon also makes an external AC power supply, and people are working out ways to run it from a 12-volt storage battery. I hope to have my hands on a D70 in the next month or two, and then I'll greatly expand my coverage of it on my web site. -- Clear skies, Michael A. Covington Author, Astrophotography for the Amateur www.covingtoninnovations.com/astromenu.html |
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