Those small scopes make a little more sense now. But if you want to photograph dim things, you want a telescope with a fast focal ratio, since focal ratio affects exposure time. So if you want to see dim things, you’ll want a larger aperture telescope. As much as you may try, your eyes cannot take long-exposure images.
I took this daytime photo of the moon by stitching together six photos: The Nexstar 8SE cannot fit an entire full moon in frame.
The Andromeda Galaxy is a little bit bigger than that in our sky! So, if you want to photograph it, and your telescope has so much magnification that it can’t even fit the entire full moon into a single frame, it has zero chance of capturing the Andromeda Galaxy. Imagine a full moon, then copy and paste that moon six times wide and three times tall. For example, most people don’t realize how big the Andromeda Galaxy is in the sky because you generally can’t see it with your naked eye. So the desired combination of these elements depends upon your stargazing targets. Camera owners are very familiar with f/stops and know that “fast’ lenses will let a lot of light in, allowing shorter exposure times. Divide aperture into focal length to get focal ratio. The dimmest object you can see is determined by aperture.įocal Ratio (f/stop) directly affects how long of an exposure you will need to take to photograph a given object. So, a 400 mm telescope with a 10 mm eyepiece magnifies 40 times.Īperture directly affects brightness and detail. Divide your eyepiece into your focal length for magnification. The things to keep in mind are:įocal length directly affects magnification. I wrote a separate blog post about what to consider when buying a telescope. Many of these smaller scopes had modest focal lengths in the 250 mm - 450 mm range, compared to the Nextstar 8SE’s 2032 mm. The Nexstar 8SE has an 8” (203 mm) aperture. Bigger must be better for astrophotography, right? Well, I think I was surprised to learn that most photos I viewed were taken with relatively small (80 mm - 100 mm aperture) telescopes. So, I think my biggest misconception about astrophotography was that all of those amazing internet photos were taken with giant telescopes.
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