The sky is full of amazing celestial objects, but what scope to use usually boils down to a choice between Widefield (short focal length) or Narrow Field (long focal length) setups. Often people ask which is better and truthfully both can be good, but selecting the right focal length can be one of the most critical decisions in astrophotography, as it determines not just what you see, but how much you’ll struggle to capture it.
Having used both for many years, I thought I’d give a breakdown of the pros and cons I’ve run into for each to help you decide which path fits your goals.
1. Widefield Astrophotography
Typically involves focal lengths between 135mm and 500mm (e.g., small refractors or telephoto lenses).
The Pros:
- Forgiving Tracking: Because the field of view is so wide, small errors in your mount’s tracking are less noticeable… this includes things like wind or movement around the mount itself. For very wide field you often don't need expensive "auto-guiding" setups to get round stars.
- Framing "The Big Picture": These scopes excel at capturing massive nebulae (like the North America Nebula or the Rho Ophiuchi Cloud Complex) that simply won't fit in a larger telescope.
- Portability: Widefield rigs are usually lightweight, making them perfect for traveling to dark-sky sites. They can often run on smaller, cheaper star trackers.
- Faster Setup: They are generally less sensitive to temperature changes and easier to balance. Quicker to physically set up and tear down.
- Tighter stars: Widefield scopes are often less affected by atmospheric seeing conditions, typically resulting in tighter stars with less of an airy disk around them.
The Cons:
- Subject Size limitations: Smaller targets like planets or distant "island" galaxies will look like tiny dots or smudges.
- Pixel Scale Issues: If your camera's pixels are large and your focal length is very short, you may end up with "blocky" or undersampled stars.
- Less resolution: Fine details can be lost; close stars can sometimes “bleed” into each other.
Cocoon Nebula (IC 5164 or C19) @ ~500mm focal length using asi2600mc (APS-C sensor)
2. Narrow Field (Deep Space) Astrophotography
Typically involves focal lengths of 1000mm to 3000mm+ (e.g., Schmidt-Cassegrains or large Newtonians).
The Pros:
- Incredible Detail: This is how you capture the swirling dust lanes inside the Whirlpool Galaxy or the fine filaments of a planetary nebula.
- Planetary Capability: If you want to see the Great Red Spot on Jupiter or the divisions in Saturn’s rings, you need the high magnification that only a narrow-field scope provides… though seeing conditions can at times allow for smaller scopes to see these with less detail
- Object Variety: While widefield is limited to large nebulae, the universe is full of thousands of tiny galaxies that only a long focal length can reach.
The Cons:
- The "Tracking Tax": Long focal lengths magnify everything—including the tiniest vibrations or mechanical errors in your mount. You must have a high-end, heavy-duty mount and a secondary "guide camera" to keep stars from trailing.
- Slow Focal Ratios: Many narrow-field scopes (like SCTs) are "slow" (f/10), meaning you have to take longer exposures to capture the same amount of light as a "fast" widefield refractor.
- Atmospheric Sensitivity: On nights with poor "seeing" (turbulent air), your images will look blurry because you are essentially magnifying the shimmering atmosphere.
Cocoon Nebula (IC 5164 or C19) @ ~3000mm focal length using Canon XSi (APS-C sensor)
Which Should You Choose?
- Choose Widefield if: You are a beginner, you love sweeping vistas of the Milky Way and massive nebulae, or you want a rig that is easy to transport and set up.
- Choose Narrow Field if: You are an experienced hobbyist with a sturdy mount, you have a permanent observatory setup, or you are obsessed with hunting small, distant galaxies and planets.
Pro-Tip: Many astrophotographers eventually own both—a widefield refractor for summer/winter nebulae and a long-focal-length scope for "Galaxy Season" in the spring/fall.
As always, reach out to us at support@telescopescanada.ca if you have any questions… we’re always happy to help
Narrow field examples
Messier 51 @ 2800mm fl
Messier 57 @ 2800mm fl
Messier 87 relativistic jet @ 2800mm fl
Widefield examples
Iris Nebula (NGC 7023) @ 530mm fl
Heart and Soul nebula (IC 1805 & IC 1848) @ 243mm fl
Messier 17 and Messier 16 @ 460mm fl