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Recent astrophotos with 10 inch scope

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  • Recent astrophotos with 10 inch scope

    M31, the Great Galaxy in Andromeda




    The Cocoon Nebula. By chance, it is positioned in a small break in the star clouds of the Milky Way.




    The Wild Duck cluster in the Milky Way Galaxy.



    The star Altair, a class A7 blue star, 22 light years from Earth.

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  • #2
    Spectacular pictures !
    Gary


    Appearance is Everything...

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    • #3
      What's causing the rays/spikes in the Altair star pic?

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      • #4
        Those are diffraction spikes that are caused by the secondary mirror support. In my design I use three paired tension bands which then cause diffraction spikes on both sides of centre resulting in the six pointed star effect. The Hubble uses a 4 blade mount and because the blades are opposite each other across the centre it only makes 4 spikes. I don't mind the six double spikes as I think it looks neat and I don't care if it obscures nearby stars. It's a kind of signature for my telescopes. It only shows up on really bright point sources such as Altair which is one of the top 20 brightest stars in our sky.

        This is the secondary support, also called the spider.

        Last edited by Evan; 09-29-2011, 10:17 PM.
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        • #5
          Evan,
          Great pictures. I am glad you got some good viewing.
          Thanks
          Dave

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          • #6
            Why do some of the stars look elliptical?

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            • #7
              That is called coma. This is a fairly fast mirror. Any optical system produces a curved field of view. The faster the optics the greater the curve. That must be projected on a flat surface (the sensor) so if the focus is slightly out stars around the outer part of the field will be more out of focus than the centre.

              I am finding that the focus on this scope is changing with temperature which is to be expected since it is all aluminum. I made my previous 6" scope with carbon fibre structure for that reason since it has nearly zero coefficient of linear expansion with temperature. I didn't realize how effective that is until using this scope. The focusing on this scope is very critical. It needs to be within about .001" of optimum.

              I am using a remote joystick control to adjust focus but it is too fast moving. I need to make a PWM speed control for the focus motor so it will creep when adjusting focus. I am also toying with the idea of an autofocus system that will sense the apparent star image size and adjust automatically between exposures. You will note that the image of Altair exhibits almost no coma as it was perfectly focused. That was easy since it was a single one minute exposure. The exposures for M31 were taken over about 2 hours as I had a few clouds scudding past. Over that period the temperature usually drops considerably during a clear night.

              In all, the moving mirror focus system is a big improvement over an adjustable eyepiece, especially when carrying a camera.
              Last edited by Evan; 09-30-2011, 10:13 AM.
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              • #8
                Attempts have been made to make electric guitars from aluminum. They do not stay in tune due to expansion/contraction. Especially under hot stage lights,these guitars are a fit to keep in tune. And,they feel cold,needless to say,unless you are in Florida,where some were made.

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                • #9
                  Awesome looking pictures, Evan. Do you have a pic of the whole telescope?
                  What kind of finish did you use on black sides of the body? Is that Parkerizing?
                  I cut it twice, and it's still too short!
                  Scott

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                  • #10
                    If the temperature change proves to be too much of a problem I can easily change the six forward struts to epoxy/carbon fibre to eliminate most of the problem. Most of my observing is done in winter when the night temperatures are more stable. This winter will tell the tale.
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                    • #11
                      See short video here:

                      http://youtu.be/yO_r9-yHgFA

                      The black finish is crinkle paint on the outside and black felt on the inside.
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                      • #12
                        Won't the stars move over the 2 hour exposure time period? Does the telescope automatically move with them? I may have missed the point as I don't understand much of this stuff but I find it fascinating none the less. I think it would be really neat to build my own telescope especially since my wife would enjoy seeing the stars as much as I would enjoy building it. Any advice on how to get started in making a telescope? Thanks for the pictures.

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                        • #13
                          The scope has a very accurate tracking system to follow the apparent motion of the stars. That is really a requirement for all but the most casual viewing. For photography it is essential.

                          See this site for good information on scope construction on a budget.

                          http://www.davetrott.com/
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                          • #14
                            Looks like some coma in the pictures. Think you can use a coma correcting optic?

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                            • #15
                              That isn't necessary. It's just a matter of maintaining proper focus over time and for that I need to improve my focus controller. What would really work well would be a flip mirror to a video cam so I could focus in real time before each exposure. As the size of the objective goes up the focus becomes more critical since the resolution is better. Also, any optic in the path will result in light loss.
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