Would a super telephoto or a telescope work better?

Started Nov 6, 2012 | Questions thread
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RustierOne Veteran Member • Posts: 3,685
Re: Would a super telephoto or a telescope work better?

astromarty wrote:

As a professional photographer and astro geek I have learned a lot over the past few years of imaging. First of all: there is no clear "better" between telescopes and telephoto lenses, it all depends on what you need it for.

For moon and planets: 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:


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 Damien Peach follow this procedure and the results are stunning:


Where the 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 much 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 much more forgiving when it comes to tracking errors, so it's much easier to get nice pinpoint stars.

A decent ED lens between 180mm and 300mm is an ideal way to get introduced to Deep Sky photography - even with a full frame DSLR stars will be sharp into the corners. With 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 (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 fast telephoto lens for wide-field Deep Sky photographs. Here is some of my own work, all done unguided (meaning that I don't use an autoguider on my equatorial mount):


Good advice, Marty. And beautiful work in the above link!!

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Best Regards,

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