Telescopes or Telephoto Lenses?

As a professional photographer and confirmed astro geek I have been asked if a telescope is better than a long telephoto lens. First of all: there is no clear “better” between telescopes and telephoto lenses, it all depends on what you need it for. In general, telephoto lenses offer faster f-stops whereas telescopes offer longer focal lengths. For moon and planets: definitely get a telescope. Even with an inexpensive refractor you can get beautiful close-ups of the moon if you use a Barlow lens or eyepiece projection. Here is an article I wrote on the subject: Astrophotography on a Budget Detailed planet shots require more expensive telescopes (forget about telephoto lenses, since you will need an effective focal length of several meters). Larger Schmidt-Cassegrain types like the 11-inch Celestron or Meade are well suited for this. You will need a small video camera, take hundreds or even thousands of frames and let the stacking software (like Registax) do its magic. Great planetary photographers like Damian Peach follow this procedure and the results are stunning: Where telephoto lenses really shine is short exposure Deep Sky photography. Most refractor telescopes are anywhere between F/6 and f/11 – whereas you can get a sharp 300mm lens that performs well at F/4 or even F/2.8.  That means shorter exposures and consequently less need for a high-end equatorial mount. I have been using a fairly simple Celestron Advanced VX mount for almost two years and exposing for only 20 or 30 seconds with a telephoto lens at F/4 will reveal a wealth of stars and nebulae at ISO settings between 800 and 1600. The relatively short focal length will also be more forgiving when it comes to tracking errors so it’s much easier to get nice pinpoint stars. Here are two samples of astro images I shot with a telephoto lens (click on photo to see full frame display): See tech data for images at the end of this article. A decent ED lens between 180 and 300mm is an ideal way to get introduced to Deep Sky photography. With a DX and even with a full frame DSLR stars will be sharp into the corners. For a telescope it can actually be a challenge to get a perfectly flat field and often extra optical accessories (field flatteners/focal reducers) will be needed to achieve that goal. My advice for beginning Deep Sky photography would be to get a sturdy equatorial mount like the AVX and either a small and well corrected ED refractor (I love the Astro-Tech AT65EDQ) or a fast telephoto lens. For mosaics (sky composites using Photomerge in Photoshop) of the Milky Way, telephoto lenses are unsurpassed. In short, get both! A telescope for moon and planets, where long focal lengths are necessary to catch the finer details and a telephoto lens for wide-field Deep Sky photographs. Fast telephoto lenses are usually expensive but if your budget is limited there are many older ED lenses that are optically fantastic, like f.e. the Canon EF 300mm f/4 L and the Nikkor 300mm F/4 ED AF, which I picked up for well under $400 on Ebay (see photo of Orion’s belt and sword taken with this lens). You may not have all the bells and whistles of the newer lenses, but for astrophotography all that matters is quality optics – focus is done manually anyway (preferably using Live View if your camera has that option). Here is some of my own work, all done unguided (meaning that I don’t use an autoguider on my equatorial mount): Martin Cohen Astrophotography Clear skies!

Tech Data For The Images Above

Photo 1: M42 Orion Nebula
A wide field image of Orion’s belt and sword, shot with a 300mm telephoto lens, shows the many different nebulae in this beautiful constellation. The three bright stars of Orion’s belt are at the top of the image; the sword contains the Great Orion Nebula below and the Running Man Nebula right above it. To the left is the bright star Alnitak with two very interesting nebulae: the Flame Nebula and the Horsehead Nebula. In this photo the Horsehead Nebula was enhanced with details shot through a small telescope.
  • Constellation: Orion
  • Camera: Nikon D5100, astro modified
  • Optics: Nikon 300mm f/4 ED AF lens and AT65EDQ telescope (quadruplet)
  • Exposure: 12 subexposures of 30 seconds each at ISO1600, stacked in Deep Sky Stacker and further processed in Photoshop CS6
  • Mount: Celestron Advanced VX
Photo 2: Milky Way
In this multi-frame mosaic of the central part of our Milky Way a long exposure reveals a wealth of clusters and nebulae against a dense background of stars. Our galactic center is to the right side of the image, above the center. What appears to be a dense cloud is really a conglomeration of tens of thousands of stars at the very brightest part of our Milky Way - at a distance of 25,000 to 30,000 light years. Many Messier objects (M8, M16, M17, M20, M21 a.o.) are clearly visible. Shot in the mountains above Malibu, California on July 13, 2013.
  • Constellation: Sagittarius
  • Camera: Canon 1000D, astro-modified
  • Optics: Nikon 180mm f/2.8 ED lens
  • Exposure: 2 subexposures of 15 seconds each per frame at ISO 1600, 18 frames total, stacked in Deep Sky Stacker and further processed in Photoshop CS6
  • Mount: Celestron Advanced VX

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