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Stargazing New telescope questions

  1. Dec 30, 2008 #1
    I have just recently gotten a 8 inch dobsonian telescope. I have two lenses, a 9mm and a 30mm. I really enjoy going out and seeing the sky and I have a few questions to make my outings a little more successful.

    The way I focus the telescope is my adjusting how far out/in the eyepiece is. Whenever I have the 30mm eyepiece in, the point where it focuses is when the eyepiece is as far back as it can possibly be and its almost a little shy. Lately I have been not completely putting the lense in the eyepiece holder so that I can better focus it. So is there a reason why the focus point is as far back as possible and is there anyway to correct that? When I use the 9mm it is not like that.

    Also, I have been having trouble viewing and focusing some objects. For instance, last night I went out to view Saturn in the eastern sky. I located and began observing, but the object was very blurry and I couldn't hardly make anything out. Exchanging the 30mm for the 9mm only made things worse. The thing is that when I looked at the orion nebula in the top of the sky, it looked so good. Not blurry or anything. So I don't feel justified blaming it on the sky.

    I have read that you should leave your telescope outside for an hour to acclimate to the temperature. And I didn't do that, so perhaps that was it. Also I am doing this around lights, but I am not in direct view of the lights so maybe that could be a large effect.

    Sorry this is so long. If someone could tell me how to fix my 30mm focus or if that is normal, and maybe just general advice on to how to better optimize my viewing I would appreciate it. Thanks.
  2. jcsd
  3. Dec 30, 2008 #2


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    Lack of sufficient focus travel is not uncommon - You can buy extension tubes for that. http://www.telescope.com/control/product/~category_id=optical_aids/~product_id=05123

    Or, if you have a diagnoal, that will give you extra focus distance.
    Well, what's the difference? With the Orion nebula, you used lower magnification and the nebula was higher in the sky: both decrease atmospheric distortion (or how noticeable it is). Saturn will be much better later iin the winter when you can view it higher in the sky.
    It helps, but it is probably not a big factor at the magnifications you are using.
    That affects your ability to see contrast and dim objects, but does not affect the resolution.
  4. Dec 30, 2008 #3
    Congrats on the new scope!

    Tell more about it so I can have the proper amount of envy. :tongue2:

    You might also try this on the 30mm.

    http://www.optcorp.com/product.aspx?pid=9177 [Broken]

    A parfocalizing ring will let you match the focus of your 30mm to the 9mm if they are different by at least the thickness of the ring.

    I have never bought anything from the seller so I can't recommend.
    Last edited by a moderator: May 3, 2017
  5. Dec 30, 2008 #4
    Another thing you may consider is collimating your scope. I have a 10 inch Newtonian reflector and I collimate it about every 4th viewing session. It helps with planetary and basically overall observation.

    I prefer a laser collimator, however that is only personal preference.

    Yes, it is a good idea to let your scope (mirror) adjust to the ambient temperature. Some Newtonian’s have a small battery operated fan mounted on the mirror to expedite the temperature balance.

    A lot of these ‘little’ things will not show much of an improvement at low magnification but will certainly kick in a higher powers.

    Yes, light pollution is certainly detrimental, especially in deep sky observation.

    Have fun with it and enjoy your observations.

    See how many Messier objects you can observe, also comets, large asteroids. The skies are full of interesting 'stuff'.

    A basic tutorial site on collimating;
  6. Dec 30, 2008 #5


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    Congratulations on the scope. Lack of in-focus or out-focus travel is a common problem. You can withdraw the EP from the focuser slightly before clamping it with the set-screw, or buy extension tubes as suggested above. You have a good ratio with the 9mm and 30mm EPs. If you buy a 2x Barlow, that will give you the equivalent of a 4.5mm, 9mm, 15mm, and 30mm.
  7. Dec 31, 2008 #6
    Thank you for all the advice so far. I am going to go out again tonight to do some more observing. Id really like to see Jupiter tonight but I don't think it will happen given my horizon.

    My scope came with a laser collimator and I have been trying to collimate every time before I go out; However, the guide that came with my scope was very incomplete. In fact, the guide was actually for a previous version of the scope which was a fair bit different so that is a little bit frustrating. I am going to try to collimate again using a different guide.

    Part of my problem is that it is so cold when I go out that its hard to fiddle around with the scope because my fingers are freezing and I am also in a rush to see what I want to because my body is also cold.

    Yeah I have been looking for some messier objects. Any particular suggestions for this time of year? I have been really wanting to see some good galaxies and globular clusters.
  8. Dec 31, 2008 #7
    Oh a couple other things...

    How often do you clean your scope, what parts do you clean, and what with?
  9. Dec 31, 2008 #8


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    Sheneron, if you are going to observe in winter-time you must dress in many layers. My rule of thumb in northern climates is to dress like you are going to spend a day ice-fishing, then add at least another layer because of the relative inactivity involved in peering through a telescope.

    As for cleaning, unless your scope somehow gets exposed to lots of dirt and dust, you should just leave it alone. A bit of dust on the primary or secondary mirror is not going to degrade the image, and you can easily damage the coatings of the mirrors with improper cleaning.
  10. Dec 31, 2008 #9
    Yes, dress warm. When you are observing there is not much actual physical effort, so one can get cold rather quick (been there got the tee shirt).
    If you plan being out for some time you can purchase foot and hand warmer pouches. I find they are not the best but better than nothing.

    As for cleaning the optics, I totally agree with turbo-1. It is best to leave it alone. A certain amount of dust will not cause an observing problem.
    The aluminum coating on the optics in only in the order of 90nm ±10nm thick. It takes very little to damage the surface.
    Even the mirrors with SiO2 coating on the aluminum have their tolerable limits.

    We have a 18 inch Newtonian at our observatory. It has been in a rural unattended, unheated building now for several years and with the amount of normal usage the dust accumulation has really not affected the quality of observing.

    If however it becomes absolutely essential for one reason or another to clean the optics. The best solution is 50% distilled H2O and 50% alcohol using cotton swab material.
    The actual cleaning done very, very lightly.
    It is amazing how easy it is to mar the surface.

    Clear skies

  11. Dec 31, 2008 #10
    Alright, I will forget about cleaning the telescope.

    I am trying to collimate the scope right now, and I only have a laser collimator. I have been reading online and it seems alot of people like to use a collimator cap versus a laser. Well I also read I should collimate my collimator, which seemed like a good idea so I did. Here is a picture of how far off the laser is when I rotate it by 90 degrees:


    The markings on the bottom are inch markings, so that is quite small; however, there still is some error there. Will that little bit make a noticible difference in not quite correctly aligning my mirror? Would it be wise to invest in a different collimation device other than a laser?
  12. Jan 1, 2009 #11
    Unfortunately, I cannot see you jpg for some reason or another.

    Yes, I have used collimator caps and I find them great.

    I only use the laser primarily because it's fast. Thing is, if the scope is kept in good 'alignment' it only takes a short time to 'fine tuning' when observing. This can be done on only a couple of minutes.

    Yes, some people will use nothing but a collimator cap, some like the Cheshire sight tube.
    Personally I think it it very good.

    This may be an argumentative point, but Yes.

    I have found with mine, they can be just ever so slightly off and they will not perform as well as their potential.
    As the magnification goes up the performance can drop of almost exponentially.

    I apologize if I sound 'sticky or critical ' here, but anyone observing should have the very best views they can get. It keeps the interest and enjoyment up.

    LOL, it's like the guitar.
    If I play, the instrument has to be in true tune. If it's just a bit off, the same amount of enjoyment and sound is just not there.
  13. Jan 1, 2009 #12
    Thanks for the advice so far Waveform I appreciate it.

    So would you recommend getting a collimation cap or Cheshire sight tube? I would like to have the best collimated scope as possible and if that little uncollimated bit of the laser will make a difference then perhaps it would be better to use a more reliable method. It seems hard to get the laser collimator perfectly collimated, so I think I will look into both of those in order to get the best seeing possible.

    I used that guide and spent sometime collimating my scope yesterday. My instruction manual left out the part about adjusting the tilt of the secondary in order to reflect the light into the center of the primary. The manual only told me to get the laser collimator to reflect back onto itself properly by adjusting the tilt of the primary, but it said nothing about centering the primary with the secondary. I mean how could it leave that part out? So I did those steps and I looked at Venus and it was the best I have seen yet, and the difference of having a properly collimated scope made a huge difference with my 9mm, it was great. I am going out again tonight.

    Clear skies!
  14. Jan 3, 2009 #13
    Just a personal preference, I would use the Cheshire sight tube. Easy to use, inexpensive and quite accurate.

    Yes absolutely agreed, sometimes instruction manuals leave a lot to be desired.

    In fact I think some technical writers don't seem to have a good grasp on communication.
  15. Jan 3, 2009 #14
  16. Jan 4, 2009 #15
    Yes, It seem to be a relatively good price. Similar to the one I have.

    The thing with accessories such as this, if and when you ever get the aperture fever and decide to get to a larger scope, theses thing will work.

    Adapters such a 'T' rings for cameras, 1.25" to 2.00" eyepiece adapters and such are readily available and not expensive by any means.

    Just slightly off topic for a moment. I had the 10" Newtonian out last night. The moon and Orion nebula were awesome. I found the transparency quite good last night before it clouded over. However, it was a dress warm night.

    Yup, I did a collimation before I took it out.
  17. Jan 4, 2009 #16


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    Collimation for low power observing can be done adequately with a device like that, but I would suggest collimating with a star for high power observing or at the very least as a double-check of the laser collimation method. Some info:
    http://www.tomhole.com/Barlowed%20Laser.htm [Broken]

    Note that they suggest using a barlow with the laser.

    Here's more on the star test: http://legault.club.fr/collim.html [Broken]
    Last edited by a moderator: May 3, 2017
  18. Jan 4, 2009 #17


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    It's a good idea to avoid moisture condensation on the optics, which can happen when you bring a telescope indoors after spending time out in the cold. What do people do about this?

    My approach (in my limited observing experience) was to cap/cover the telescope and all eyepieces before bringing them back inside. My thinking is that will keep the indoor moist warm air from contacting the optics.
  19. Jan 4, 2009 #18


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    That's about the best thing you can do. Beyond that - don't use a humidifier inside.
  20. Jan 5, 2009 #19
    Yes, this really tends to be a problem when moving a scope between temps, humidity, and dew points.

    Personally I also cap the optics if I have move the scopes. However, I primarily leave the scope out.
    I have it well covered and protected.

    This is why a lot of people will build small observatories (shed's, small out building and such with sliding roofs). It minimizes moving the telescopes and also the wide swings in temperature.

    Even the 80mm refractor, I try to leave it out, much as possible.

    However, if circumstances warrant the scope must be brought in, then I agree with russ_watters unless you want to start playing around with 12volt Dew Heaters.
  21. Jan 5, 2009 #20


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    Another technique is to put the scope inside a garbage bag and close the end while outside. The scope is then packed in dry air before you bring it indoors.
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