Telescope Mounts Explained

Category: Telescope Eyepieces

  • Bino Viewing – Two eyes sees better than one

    Bino Viewing – Two eyes sees better than one

    Sometimes it seems like everybody has thrown out their eyepieces and only images the sky. Even though Astrophotography is hot there are many astronomers who wants to SEE the objects live with their own eyes. Some even acquire sets of eyepieces to be able to enjoy the wonders of the sky with both eyes…

     

    In this post I will look a bit into the subject of Bino viewing. By Bino Viewing, I mean any solution where the observer uses both eyes when observing

    • Binoculars
    • Bino-viewers –  Beam splitting device installed on a single telescope
    • Bino-Scopes – Two identical telescopes installed in parallel

     

    The post will touch the following subjects:

    • The advantages of observing with two eyes
    • The bino-viewer
    • The bino-scope
    • Telescope Mounts for Bino Viewing

    The advantage of observing with two eyes

    Relaxing and easier to see small details
    Observing with two eyes means that both eyes receive the telescopic view of the object. This is how our eyes are meant to be used, so it will for most observers feel more relaxed and natural. Small details hardly visible will be easier discerned by the brain, when the same signal is coming from both eyes. So using both eyes gives a more comfortable observing experience and allows for seeing smaller details.

    A 3D experience
    Real 3D views that you can get on terrestrial objects are not possible due to the distance of the celestial objects. But it is often reported that a 3D effect can be seen when observing with both eyes. Especially on the moon and the planets.

    Observing faint objects
    When it comes to seeing faint objects, two eyes will also do better than one eye if the light intensity is the same. If you add a beam splitter to a telescope, so that each eye only receives 50% of light, it will be more difficult to see a faint object than if you use one eyepiece on the telescope and get 100% of the light into one eye. But the difference might not be so big as it sounds.

    It comes at a cost
    Observing with both eyes means you will need extra equipment and two of each eyepiece you use.

    Let’s look at the needed equipment.

    The bino-viewer

    A Bino-viewer is a unit you install in the telescope focuser that splits the light into two eyepieces. Generally speaking a bino-viewer consist of:

    • A beam splitter
    • Sets of prisms or mirrors to direct the light to the two eyepieces.
    • Two eyepiece holders with adjustable distance to match the observers eye distance.
    • Sometimes a barlow lens can be installed in the front to help get the device in focus.

    This basic principle can be twisted to make many different versions of Bino-Viewers. I will not go into details with this but just point out that the quality of the Bino-Viewer is very important. It contains several optical elements that must be of excellent quality and correctly aligned not to deteriorate the image coming from the main telescope.

     

    Adding a Bino Viewer to an observation kit can be costly and it is necessary to get sets of identical eyepieces so the eyepiece budget doubles.

    But the experience is fantastic!!

     

    Examples of very good Bino Viewers are TeleVue Binovue, Denkmaier Binotron 27 and Baader Planetarium Mark V

     

    The Bino-Scope

    My definition of a Bino-Scope is:

    A combination of two parallel identical telescopes with adjustable exchangeable eyepieces.

    This definition excludes normal Binoculars even though some larger models come with the possibility to change eyepieces.

    Typically it will be two refractors:

    TEC-140 APO Bino-Scope on TTS-160 Panther Mount

     

    To position the eyepieces correctly many high end Bino-Scopes uses a special system from Mr. Tatsuro Matsumoto  – Erecting Mirror System (EMS)

    It is expensive to get two nice refractors but – as an example two TEC-140 APO will cost approximately 15.000 usd. To get the same combined aperture from a single telescope you will need a TEC-200 APO costing approximately 30.000 usd. So from a light intensity point of view the Bino-Scope solution is much cheaper – but of course the resolution will still be like a 140mm.

     

     

    For larger aperture, reflectors is also a possibility:

    16″ Newtonian Bino-Scope (Tom Dey)

    A large Bino-reflector can be a bit difficult to handle with collimation and alignment of the two OTA’s but the visual experience on Deep Sky Objects is out of this world.

     

    Telescope Mounts for Bino Viewing

    Binoculars

    For normal Binoculars and small Bino-scopes a completely manual mount can be enough and satisfying. Normal photo tripod style mounts can be used, but when you observe very high in the sky you will benefit from a special type made for astronomy.

    Standard  Photo Tripod & Astro parallelogram mount

    Larger telescopes and Bino-Scopes

    When the equipment gets bigger a better mount is needed. When selecting the mount there are some parameters to focus on.

    • Eyepiece position
      • One very important thing to focus on is the eyepieces position. Getting both eyes in a good and relaxed position in front of the eyepieces is extremely important. If the mount tilts the telescope sidewards – like all polar aligned mounts do –  you will end up having the head in unpleasant angles.
      • No Meridian Flip – a meridian flip will turn everything up-down making it impossible to use with a Bino-Scope

        Alt-Az mount tracking pattern
    • Tracking and goto
      • When you observe with higher magnification tracking is a must. Goto is also great even if you sometimes prefer to star-hop to the targets manually. This points to a Motorized Alt-az mount. For single telescopes with Bino-Viewer a side mounted solution is possible. For real Bino-Scopes a top-mounted solution is the best.
    • Setting up a heavy Bino-scope
      • A large aperture Bino-Scope is both bulky and heavy. Therefore it is extremely important to consider how to handle the telescope when transporting and setting up.
      • A telescope mount with a top-mounted horizontal dovetail saddle is a great help when installing the telescope. It is possible to lift the telescope up on the saddle and rest it there while locking the saddle clamps.
      • To avoid lifting the telescope up too high, a Tripod with a geared column can be an advantage.Lower the Column completely – install the telescope – raise until the wished observation height.

     

    Berlebach Planet K70 with geared column
    150mm APM APO Bino-scope on TTS-160 Panther Mount on Berlebach Planet K70 with geared column

     

    130mm Starfire EDF Binoscope on TTS-160 Panther Mount

     

     

    103mm Williams Optics Bino-Scope on TTS-160 Panther Mount
  • Galaxy hunting with Eye and Camera

    Galaxy hunting with Eye and Camera

    The winter sky with the many gas nebulas has disappeared in the western twilight. In an earlier post – Fast Deep Sky Imaging – I described how these large objects could be imaged with fast optical systems with limited focal length and large field of view. In springtime our view points away from the milky way arms and we get a free look to myriads of distant galaxies. Observing and imaging galaxies is a quite different matter as you can read in this post.

    Galaxies and dark sky

    For most unskilled visual observers Galaxies are faint hazy spots. If you try to observe galaxies from a light polluted place and don’t give you the time it takes to learn to really see these faint objects – all you will see is a faint spot – if anything at all.
    If you instead brings your telescope to a rural dark sky place and take your time to really observe the galaxies you will realize that galaxies can show many details. It is possible to see spiral arms and dark dust bands.

    Bring your telescope to a real dark

    sky site to really enjoy Galaxies.

    With the camera on the telescope this is a bit different. A dark sky is still a huge advantage but it is possible partly to compensate for a light polluted sky using filters and increased exposure time. But if you have tried to image from a dark site, you will now how much easier it is to get a good color balance and how much shorter exposure time you can use – or get much deeper with the same exposure time.

     

    Bring your telescope to a real dark sky site to shorten exposure time and get clean colors

    Galaxies and resolution

    Besides for the two large exceptions M31 – the Andromeda Galaxy and M33 – the Triangulum Galaxy (and perhaps a few in the southern sky) most galaxies are rather small in the sky compared to gas nebula. Therefore we need to “zoom in” to get at better view.

    Galaxies are small!

    Compare Horse Head Nebula complex with Whirlpool Galaxy M51. 

    Visually this means more magnification. It is often seen that galaxies are observed with wide field eyepieces with low magnification. This might make the galaxies looks brighter but it is very difficult to see any details. In stead if the magnification is increased the sky will become darker and with careful examination more details within the galaxies will be visible.

    I prefer to use magnifications around 75% of the telescope aperture in mm:

    • 100mm telescope 75x

    • 200mm telescope 150x

    • 350mm telescope 262x

    When you observe galaxies visually don’t be afraid to use a fairly high magnification.

    Photographically resolution relates to image scale and aperture. The image scale has to be large enough to allow for the details to be recorded. To be able to get decent galaxy images an image scale around 1 – 1.5 arcsec/pixel is needed. So in most cases it means you will need a focal length around 1 meter or more. Increasing the image scale further will in most cases just lead to a fainter more noisy image with no extra details. When it comes to telescope aperture 100mm is minimum and 130mm and up is preferred.

    Difference between image scale of 1.5″/pixel and 3″/pixel.

    When you photograph galaxies aim for a pixel scale around 1-1.5 arcsec/Pixel

     

    But remember tracking, focusing and seeing is usually what really sets the resolution limit.

    Read post about about guiding

    A galaxy hunting starparty – all alone (corona time)

    Luckily the lockdown in Denmark was not too harsh so it was ok for me to go to a rural place for an observation night. To really get the best of two worlds I brought both a visual setup and a photographic setup.

     

    Short video presentation of Astrophoto setup

     

    Astrophoto Setup

    140mm f/7 (FL 980mm) TEC APO

    Atik 460 sx camera with Baader LRGB filters

    Televue TV60 as guide scope

    TTS-160 Panther Mount with telescope rOTAtor

     

    Short video presentation of Visual setup

     

    Visual Setup

    Celestron C9.25 SCT

    13mm Televue Ethos Eyepiece, magnification 181x

    TTS-160 Panther Mount

     

    Visual results of the night

     

    The sky turned out to be very clear and quite dark – very good for visual observations. I started in west and worked my way eastwards in the sky. Here is a list of objects I observed:

    • All Messier galaxies in Leo. The Leo triplet M65, M66 and NGC 3628 was fairly easy to see. The different shapes of M65 and 66 was obvious. NGC 3628 is large but with a much lower surface brightness.
    • In the Virgo cluster (in Virgo and Coma Berenices) I observed so many galaxies I can’t remember them all. I used Skysafari on my Iphone and just jumped from galaxy to galaxy. Amazingly most of the small (and to me unknown) NGC catalog galaxies were visible even though only as dim spots.
    • In Ursa Major I also observed many Galaxies and the Planetary Nebula – “the Owl”. The “eyes” were visible with adverted vision.
    • And just to mention a few of the “big ones”
      • The “Needle galaxy” NGC 4565. Stretching across the central FOV with an outer shape as know from images. Not certain I could see the dark dust band.
      • The “Black Eye Galaxy” M64. Large elongated and getting brighter towards the central parts. The dark dust cloud (the eye) visible with adverted vision.
      • The “Whirlpool Galaxy” M51. The two galaxies are very easy to spot close together. In M51 there are lots of dark areas outlining the spiral arms. Quite large in the FOV.
      • I ended the night observing Globular Clusters. M13 was amazing resolved to the center.

    Astrophotos from the night

    While I enjoyed the sky visually the AP rig was gathering photons. The main target of the night was “Markarians Chain of Galaxies”. The following subs were taken:

    •  23 x 300 sec in Luminance
    • 5 x 300 sec in RGB
    • I ended the night by taking sky flats against the morning twilight sky.

    Markarians Chain – click on image for large size.

     

    Before the morning twilight I also shot M13 – 8 x 120 sec in RGB – click on image for larger size

  • Telescope Eyepiece Basics

    Telescope Eyepiece Basics

    Below is the slides from a presentation I have held several times at different Starparties. The presentation gives a basic introduction to eyepieces and how to select the right ones for your telescope.