See how a deep-sky target frames on a Micro Four Thirds camera at any focal length. Pick a lens or type a focal length, choose a target, and the frame below shows it drawn to scale inside your sensor's field of view.
mm
Actual focal length, not the full-frame equivalent.
Frame coverage
Target size in frame
FF equivalent
Frame width by focal length
Horizontal field of view on the M43 sensor (17.3 × 13mm), in degrees, at common focal lengths. Shorter lenses fit wide targets like Andromeda and the Heart Nebula; longer lenses isolate small targets like the Ring Nebula.
Focal length
FF equivalent
Horizontal FOV
Vertical FOV
7.5mm
15mm
98.1°
81.8°
12mm
24mm
71.6°
56.9°
25mm
50mm
38.2°
29.1°
45mm
90mm
21.8°
16.4°
75mm
150mm
13.2°
9.9°
100mm
200mm
9.9°
7.4°
150mm
300mm
6.6°
5.0°
300mm
600mm
3.3°
2.5°
How framing works
Every camera sees a fixed angle of the sky, set by the sensor size and the focal length of the lens. On Micro Four Thirds the sensor is 17.3 × 13mm, so the horizontal field of view is the angle whose tangent is half the sensor width divided by the focal length. A short lens takes in a wide angle; a long lens narrows it down. The target itself has a fixed apparent size in the sky, measured in arcminutes (one arcminute is one sixtieth of a degree). Framing is simply the target's apparent size compared to the angle your camera covers.
Matching the lens to the target
Deep-sky targets vary enormously in apparent size. The Andromeda Galaxy spans about three degrees, six times the width of the full Moon, so it needs a short lens to fit. The Orion Nebula is around one degree across and frames well on a normal-to-short telephoto. Small planetary nebulae like the Ring Nebula are tiny, around one to two arcminutes, and stay a small dot in the frame even at 300mm. There is no single best focal length for astrophotography; the right one depends entirely on the target.
A note on the crop factor
The focal length used here is the real number printed on the lens. Because the M43 sensor has a 2x crop factor, a 150mm lens frames like a 300mm lens on full frame. That reach is an advantage for small targets: you get a tighter view of a distant galaxy with a shorter, lighter, cheaper lens than a full-frame shooter would need. For very wide targets it works the other way, and you reach for genuinely wide lenses.
Why this is only the framing, not the whole story
This tool answers one question: will the target fit, and how large will it appear. It does not tell you whether you can capture it well. Faint galaxies and nebulae need long total exposure time, dark skies, and usually a star tracker to allow exposures longer than the few seconds an untracked tripod permits. For the untracked exposure limit on your body, use the Astro Exposure Calculator. Apparent target sizes here are the commonly cited bright extents from published catalogues; the faint outer regions of many objects extend further than the figure shown.