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Thread: 8" Newtonian-astrograph vs a 10" Dobsonian

  1. #1
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    8" Newtonian-astrograph vs a 10" Dobsonian

    I am new in astronomy and am very confused between an 8" f/5 Newtonian-astrograph and a 10" f/5 Dobsonian for my first telescope. I prefer deep-sky viewing but would also like to do some astrophotography.

  2. #2
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    Welcome to the board. First up, you really should look for a local astronomy club, find out when they have a star party and go see what they have, try scopes out and talk to people. A big issue for newcomers is that they often get a telescope that isnít really practical for them. For instance, a big telescope can be a pain to transport and set up so might not get much use. Even if you have dark skies at your home, you might still find a large scope to be too much bother to use often.

    If you go to a star party you might find something you hadnít considered and that would be better for you.

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  3. #3
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    Welcome to the CosmoQuest forums, hisuv19. I have moved this thread to the Astronomical Observing, Equipment and Accessories forum where you're more likely to get answers to your questions.

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  4. #4
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    For any astrophotography other than snapshots of the Moon and bright planets, an equatorial tracking mount is necessary. A mount that is rigid enough do the job with an 8" f/5 Newtonian will be expensive and heavy, vastly more so than the Dob. I agree about picking brains at an astronomy club before deciding what to buy.

  5. #5
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    Oct 2011
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    I completely agree with Van Rijn and Hornblower. Start with your local astronomy club. You will learn more about your topic there and faster than by any other means.

    A couple observations (pun intended):
    [1] Equatorial mounts (mentioned by Hornblower) have a steeper learning curve than alt-az mounts (like a Dob has or most computer-controlled SCTs have). IMHO, most newbies should not start with an equatorial mount. There is a lot to learn when you begin about using a telescope and adding an equatorial mount just adds to the burden. That being said, my first telescope was on an equatorial mount (5" SCT on single arm fork with wedge). However, I already had quite a few years of experience with my dad when he was in our local club and I am an engineer with excellent 3-D reasoning skills. Even so, learning an equatorial mount was more work and more trouble than an alt-az mount. The 5" now sits on a Celestron Advanced VX German Equatorial Mount and it's what I use for my rare forays into astrophotography. My two larger scopes (8" and 11" SCTs) and my wife's scope (10" Dob) all have alt-az mounts. I am primarily a visual observer and public star party host and I find that computerized alt-az mounts work best for both.
    [2] "Easy" astrophotography includes star trails, the Sun, and the Moon. For star trails, put the camera with a wide angle prime lens or wide angle zoom lens on a tripod and leave the shutter open for tens of minutes up to several hours. This is easy with a film camera with a mechanical bulb setting, doing a digital time lapse and stacking the images, or using a camera with a Live Composite feature, like my Olympus E-M1 Mk II. The attached image is from this past Friday. For Sun and the Moon, exposures are similar to daytime photography, so an equatorial mount is not required. For the Sun, you need a solar filter that fits on the front of the telescope. I use Baader film solar filters, but there are other types, both glass and film.
    [3] "Hard" astrophotography includes planets (you need lots more focal length than most telescopes provide) and deep sky (long exposures and the need for an equatorial mount). For deep sky, most astrophotographers recommend starting with wide field (camera and lens on an equatorial mount or piggybacked on an equatorially mounted telescope), then moving into a mid-range focal length (say 200 to 600 mm), before tacking small objects at high magnification. I know one professional photographer who gave up on high-end astrophotography as being more trouble than it's worth. On the other had, I know non-photography amateurs who excel at high-end astrophotography and enjoy the time (lots of time) spent. I have purposely limited my astrophotography to "easy" and the easiest parts of "hard" because anything more takes away from time spent at the eyepiece.

    Fred

  6. #6
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    OK, the image didn't load, so I will point you to a public photo album I made on Facebook for my astronomy club's page. See https://www.facebook.com/fred.luskii...4740126&type=3

    This four-image album also includes a demonstration of field rotation and two waterfalls. As best I can tell, the waterfalls have nothing to do with your query. :-)

  7. #7
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    As it happens I cannot relate to difficulty in learning how to use an equatorial mount, while I must stress that I do not belittle those who do find it difficult. My dad got a 3-inch Edmund Scientific reflector when I was a budding amateur astronomer at age 10. I had been an eager beaver observer with naked eye and binoculars for nearly a year, by which time I fully understood the pertinent geometry. Having said that, I know now that a Dob would have been easier to use than that joke of an equatorial mount that came with the telescope. Here is an ad from a magazine of that era.

    Edmund 3-inch 1958.jpg

    In this view we are facing roughly east, with Polaris off to the left. We had a blast looking at Jupiter, Saturn and the Moon, but when I wanted to look at Mizar and Alcor it became apparent that the mount was useless for anything more than about 25 degrees north declination. We had to turn the tripod around and use it as if it were a Dob on the side of a steep hill. That is when my dad built a German type mount with the help of a machinist where he worked. It had a worm drive in right ascension and a tangent screw drive in declination, as do many low end mounts today. If he had not had the benefit of the machinist, we could have made a perfectly good mount from pipe fittings, as was illustrated recently in Sky and Telescope. It would not have had the slow motion controls, but for visual work that is not that big a deal.

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