Interested in a Telescope for Astrophotography....

Discussion in 'Photography Equipment & Products' started by barfastic, Aug 19, 2009.

  1. barfastic

    barfastic TPF Noob!

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    Hey guys,

    Im interested in buying a telescope for stargazing and the occasional astrophotography.

    Ive been reading up on different telescopes, and im between a Meade ETX-125 AT and a Celestron NexStar 6 Se

    Details:
    Meade ETX125 - 899$
    1900mm Focal Length
    125mm (5.0") Aperture
    Focal Ratio f/15

    Celestron Nexstar 6 Se - 799$
    1500 Focal Length
    150 (5.91") Aperture
    Focal Ratio f/10

    They both come with PC software to point at constellations etc, and both have tripods/bases for mounting.


    Im leaning more towards the meade as i have heard from others that it is a great telescope, and it seems it has available t-mounts for mounting a dslr on it.

    What do you guys think?

    Im also wondering, since my camera is a cropped sensor, will the focal length be at 2850mm (using the meade)?

    im curious as to how many pics im gonna have to take to get a complete moon pic :p

    any ideas, or information would be great.

    Thanks in advance
     
  2. KmH

    KmH Helping photographers learn to fish Supporting Member

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    Even in astronomy aperture is the name of the game. If you can double the aperture you gather 4 times as much light.

    Speed (f-stop) is also a consideration.

    The Celestron has the edge in both with 6" to the Meade's 5" and f/10 to the Meade f/15.

    There is the consideration of the slightly differing designs, a Maksutov-Cassegrain (Meade) to a Schmidt-Cassegrain (Celestron). The Meade, at f/15 will have a slightly smaller Field-of-View than the Celestron and is at it's lower limit for f/stop. Maksutovs perform a bit better at f/20 to f/23 or so.

    However the Celestron will have a bit more field curvature, but an Angular-Field-of-View of over .8 degrees (approx. 50 arcminutes). The Moon's AFV ranges between 29 and 34 arcminutes so you'll only need 1 exposure to capture a full moon.

    Either will require a good solid mount to return good images. If you decide to image anything that requires any appreciable shutter times, you'll need a good driven polar mount to negate the effects of Earths rotation during an exposure.

    Based on your intended use I would recommend the Celestron.
     
  3. benhasajeep

    benhasajeep TPF Noob!

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    About 11 years ago I purchased a Meade ETX-90. There was enough slop in the lower gear drive I took it back the very next day. It was a sealed box so either its not quite that good of a design, or it was a bad unit. Either way I would stay away from the ETX line.

    Also not sure if your wanting to use a slr camera or a telescope camera, but if your talking slr. I think the gear train is a little small on the ETX for sure. I don't know the specs on the Celstron.
     
  4. gryphonslair99

    gryphonslair99 Been spending a lot of time on here!

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    What you really want is this.
    [​IMG]
     
  5. Josh66

    Josh66 Been spending a lot of time on here!

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    Yup. Neither of those are very fast (f/10 & f/15), but you can still get some decent shots from them...

    My telescope (1200mm, f/13.3) is pretty slow, but it still works pretty good for the moon.
     
  6. Dwig

    Dwig TPF Noob!

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    For stars, and other point-like light sources, the f/stop, or what is classicly refered to as the "focal ratio" when refering to astronomical telescopes, is of absolutely no importance to the image of the stars themselves. It only influences the exposure of diffuse light sources (e.g. nebulae, the moon, planets that resolve as a disk, sky glow/light polution, ...). What is important is the actual aperture (aperture = hole) area. A 125mm aperture scope creates a brighter star image (images dimmer stars) than a 90mm scope regardless of focal lenght or focal ration (f/stop). The aperture diameter is a limiting factor for resolution; the larger the diameter the greater the potential resolution.

    Also, for astrophotography you need a scope with an equatorial mount rather than an alt-azimuth mount. Many of today's less expensive scopes with computerized auto-tracking using the latter. While they can do a good job of keeping the targeted star centering in the image field, the image field rotates around the center axis as the mount tracks the moving star field. This causes everything in the image other than the one star dead center (if there is one) to blur in long exposures. Only a very well aligned equitorial mount will keep the whole image steady during the long exposures necessary.

    This need for an equitorial mount is true even when mounting a camera with a conventional lens to the outside of the scope for what is called "piggy-back" astrophotography. Instead of shooting through the scope you are just using its motor driven mount to keep the star field stationary. Many of the better fast prime lenses can deliver some excellent wide field images when used this way. Almost any focal length can be of use. I made a decent image of Halley's Comet, now many years ago, using an 85mm f/1.4 Nikkor on a Nikon F3 body piggy-backing on a Celestron scope with one of their German Equitorial mounts.
     
  7. Garbz

    Garbz No longer a newbie, moving up!

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    What you want is a good telescope for viewing. Nearly all semi decent to decent telescopes come with camera attachments these days. When you have a good telescope and a camera attachment there are far more important factors at play.

    The accuracy with which you can track the sky. The exposure duration you're capable of without blowing your sensor or introducing excessive noise. I even saw a DIY cooler box for exactly this purpose. Camera peltier cooler - Hack a Day

    Bottom line is if you can see something, with the right gear and technique (image stacking) you can photograph even more. Check that link, follow the link to the creators webpage, and poke around there. There's loads of information about image stacking software, noise, and telescope reviews onit.
     

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