Astrophotography - telescope and other questions

Discussion in 'Digital Photography' started by GeeYouEye, Nov 11, 2006.

  1. GeeYouEye macrumors 68000

    GeeYouEye

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    #1
    I have always been interested in astronomy, and this December I will be traveling through parts of the country with little light to no light pollution, and would like to do some basic astrophotography; stars, constellations, the planets, maybe some star trails (I know, not really astrophotography). At the moment, I'm planning to do the photography with a Nikon D70, and have been researching telescopes, mostly what I can find on Craigslist for under $1000, which means Maksutov-Cassegrain telescopes <= 8" (I want a reflector). Any recommendations along these lines would be helpful (I'll certainly consider Newtonian or other reflectors).

    Part 2 of my question is regarding the D70, and specifically, getting decently long exposures. It's got a bulb mode which I've made liberal use of in the past for star trails (Yosemite is a great place for this); however, occasionally, my not completely steady pressure on the camera, despite the tripod, ruined a few several-minute exposures. So my questions: a) can the bulb mode be changed to a timer mode (press the button once to start, press again to stop), b) if not, would the wireless remote Nikon sells be of help, and c) am I overlooking any options here.

    Thanks.
     
  2. cube macrumors G4

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    #2
    I have a Meade ETX-90 but it's not really for astrophoto, as the motor has plastic gears. So, not surprinsingly, there's no way to autoguide it, AFAIK.
     
  3. Abstract macrumors Penryn

    Abstract

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    #3
    Yeah, I always wished Bulb mode worked in that fashion instead. I think the remote is the perfect solution from the sound of things, but if not, someone with experience in this field will need to tell you.
     
  4. VictorM Guest

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    #4
    The wireless remote (ML-L3) can be used to turn the bulb setting into a "time" setting - press it once to open the shutter, press it again to close the shutter.

    If you have the wired remote (MC-DC1), it has a lock-switch on it that lets you lock the shutter open, but you need the D70s to use the the wired remote.

    There is some upper limit to how long the shutter will stay open on the d70, I've heard it's 30 minutes.

    Another technique I've read about is to take many shorter exposures and combine them later, sort of like doing time-lapse photos of the sky. Never tried this myself, but I've seen it suggested as a way to get around amp noise and also to let you get much longer exposures than the 30 minute limit will let you take.

    An issue to consider is that the IR filter on the camera will tend to block hydrogen-line emissions of nebula - it would work okay for reflection nebula though . Not sure how bad of an issue this is, as I don' t have the means to try it myself. This is not specific to the D70, as all DSLR will have this problem to varying degrees (unless there are some that don't have IR filters??).
     
  5. tech4all macrumors 68040

    tech4all

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    #5
    You didn't mention if you have this, but I assume you may already know. Do you have the necessary adapters for the camera and telescope? A T-ring and t-adapater.

    I've personally have never done astrophotography (expect from shots from a camera alone on an extended exposure) but have been interested in doing it one day. When I was about to start they told me the moon and planets were good things to start out with. Then you could work your way up to nebulas and galaxies. Another thing I was once told was to put the lens cover of the telescope over the opening of the scope, release the shutter, then after about a second remove the cover. That will eliminate/reduce and shake caused by releasing the shutter.

    Good luck! :)
     
  6. hqsbud macrumors member

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    #6
    Most, if not all, DSLRs have mirror lock-up mode which makes the shutter vibration very, very minimal, and I normally use it for astrophotography. Besides, a light touch on my telescope (a 4" Celestron cassegrain focus) makes it jiggle, so taking off the telescope lens cap would be like an earthquake.
     
  7. GeeYouEye thread starter macrumors 68000

    GeeYouEye

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    #7
    I don't have the adapters, but I know which ones I need, generally.
     
  8. ChrisA macrumors G4

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    #8
    [What kinds of subjects do you want to photograph? It makes a huge difference if you want to shoot subjects in the Solar System or outside of it. Basically if you shoot the moon or a panet the subject is in sumlight, just like if you shoot a normal photo here on earth. Exposures are reasonable and like what you are used to, after all, sunlight is sunlight.

    Deep space objects are very faint and the DSLR is not as well suited to those subjects. First off the DSLR is filtered, next it is not cooled so exposure time is limited. You can take many exposures and "stack" them later using the computer. The effect is about like a long exposure.

    You do need a mount that can track the sky. This is the most expesive part of the system. It will ned to be a high grade equatorial mount.
    If not equatorial then you need a field rotators for the camera which likely costs more than the camera.
     
  9. ChrisA macrumors G4

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    #9
    Touching the scope to remove the cover will shake it FAR more then a mirror slap. By like 1000 times. A better trick is to use black cardboard. Hold the cardboard a few inches away from the scope but blocking the view of the sky. trip the shutter, wait a few seconds then move the cardboard out of the way. But this is a deep space technique. For the moon exposures are like they are here on Earth. For the Planets do yourself a BIG favor and buy a web cam. Skip the DSLR. People are getting far better results with webcams. The size of the CCD on the D70 is a total waste and the pixels are to far apart. Webcams are a better technical match up and they can take thousands of frames that are used in post processing.

    A DSLR can be used for deep sky work if you have a dark site and a brighter subject.
     
  10. tech4all macrumors 68040

    tech4all

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    #10
    Sorry, I wasn't clear what I meant.

    That's what I meant. Only with the lens cover. But cardboard could work to, in fact if it's larger that the lens cover, it would probably be even better to ensure that the entire lens is covered. :)
     
  11. GeeYouEye thread starter macrumors 68000

    GeeYouEye

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    #11
    Forgive the ignorance, but why won't an Alt/Azimuth mount work?
     
  12. GeeYouEye thread starter macrumors 68000

    GeeYouEye

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    #12
    Interesting. Do you have any more information on this?
     
  13. Over Achiever macrumors 68000

    Over Achiever

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    #13
    I think his thousands of frames comment is referring to stacking the images like this:
    http://www.cloudynights.com/item.php?item_id=1044

    I personally thought the larger dSLR sensor was a good thing, but not necessarily the case? I would just bin the CCD photosites, drop the resolution from 6-10 MP to 1-2 MP while increasing dynamic range, and the larger sensor in relation to P&S/webcams would introduce less noise. That's just what I thought anyway.

    Here's another reference link:
    http://www.fvastro.org/articles/digital/
     
  14. GeeYouEye thread starter macrumors 68000

    GeeYouEye

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    #14
    Thanks.

    Anyone know if it's possible to use an iSight to that end?
     
  15. GeeYouEye thread starter macrumors 68000

    GeeYouEye

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    #15
    Bump. Anyone have a reason for why one needs to go with an equatorial rather than Alt/Azimuth mount?
     
  16. hqsbud macrumors member

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    #16
    The Alt/Azimuth mount, while it'll keep the object centered in the eyepiece, the object can appear to rotate because of the way the tracking mechanism works. The equatorial mount always keeps the object not only centered, but also rotationless.

    That's my understanding anyway. I've so far not been able to align my telescope on an equatorial mount with any great success. I need to spend more time on that.
     
  17. ChrisA macrumors G4

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    #17
    That's exactly it. If you go with an non-equatorial mount you will need a a motorized device to rotate the camera durring the exposure. On a very large telescope this pays off but on a smaller scope that a normal person is likey to buy the equatorial mount is tha way to go.

    It's easy to visualize this. As a subject moves across the sky it's northmost point always points to the north start but one half of the night itis to the left of the noprth start and the other half it is to the right, so it's north-most side appears to rotate. What really happens of course is the Earth rotates and you need to rotate the camera's sensor in the other direction. The equatorial mount does this by having one of it's axies alighed with the Earth's axis.
     
  18. emw macrumors G4

    emw

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    #18
    I missed this thread earlier, but I, too, have the Meade ETX-90 telescope, paired with the Canon DR XT. It's a decent combination, but it's hard to do deep sky stuff. I have managed to get some decent shots of the moon, though.
     

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