Down Imaging vs Side Imaging: How Each Works and When Side Imaging Finds More Fish
Both views turn sonar into photo-like pictures, but they look in different directions. Here is what each does well, where each falls short and how to use them together.
Down imaging shows a detailed, photo-like slice of what is directly under the boat, so it is best for identifying cover and seeing fish in relation to it. Side imaging scans out to both sides and draws a wide strip of bottom, so it is best for searching: finding rock piles, brush, bait and fish you would never drive over. On larger waters, side imaging usually finds more spots faster; down imaging and regular 2D sonar then confirm what is there.
How imaging differs from regular sonar
Standard 2D sonar uses a cone-shaped beam and shows echo strength, which is why fish appear as arches and the bottom as a colored band. Imaging transducers send a thin, fan-shaped beam at higher frequencies, from several hundred kilohertz to more than 1 megahertz, so they draw sharp outlines and shadows instead of blobs. The basic trade-off never changes: higher frequency gives more detail but less range.
The brand names differ. Garmin uses ClearVü for down and SideVü for side; Humminbird uses Down Imaging and Side Imaging, with MEGA versions at higher frequency; Lowrance uses DownScan and SideScan, and its Active Imaging transducers provide both.
Down imaging: detail under the boat
Down imaging aims a thin beam straight down, narrow from front to back and wide from side to side. It is good at:
- Showing brush piles, standing timber, rock and grass with recognizable shapes.
- Separating fish holding tight to cover from the cover itself.
- Showing bait schools and their shape and density.
- Working at slow speeds, for example when idling over a brush pile or fishing vertically.
Its weakness is coverage: it sees only what you pass over. Fish usually appear as small white dots or dashes rather than arches, which is why many anglers run down imaging in a split screen next to 2D CHIRP. Our guide on how to read a fish finder covers the 2D side of that pairing.
Side imaging: searching wide water
Side imaging fires thin beams to the left and right. The image builds line by line as the boat moves, like a scanner, and shows the bottom to both sides from above. Objects cast acoustic shadows away from the boat, and the shadow length hints at height: a standing tree throws a long shadow, a small rock a short one.
Side imaging is the better tool when you need to:
- Scan a long bank, flat or ledge without driving over every foot of it.
- Find isolated cover, such as a single brush pile, a rock pile or a sunken boat, that does not appear on maps.
- Locate bait and fish off to the side in shallow water, where driving directly over them can spook them.
- Trace grass edges, channel swings and changes in bottom type.
Its main blind spot is directly below the boat, where the two side beams leave a dark band down the middle of the image. Down imaging and 2D sonar fill that gap.
Frequency and range trade-offs
| Frequency setting | Detail | Range | Typical use |
|---|---|---|---|
| Around 455 kHz | Lowest of the imaging bands | Longest | Deeper water and scanning far to the side |
| Around 800 kHz | Higher | Shorter | Shallow to moderate depths with sharper pictures |
| Around 1 MHz and above (MEGA, UHD) | Highest | Shortest | Shallow water and close-up detail |
For reference, retailer spec sheets for Humminbird’s MEGA Side Imaging+ transducers list up to about 800 feet side to side at 455 kHz and about 400 feet in the higher MEGA band, and Garmin’s sonar specifications list its Ultra High-Definition SideVü at 1,200 kHz. Those are maximums. Real-world range depends on depth, bottom type and water conditions, and the sharpest images come from well inside the maximum range.
How to get clean side images
- Run slow and straight. Turns smear and bend the image. Hold a steady, slow speed, and check your manual for the speed range its imaging is designed for.
- Match the range to the job. A long range in shallow water wastes screen space; pull the range in to see more detail on each object.
- Run parallel to structure. Make passes along a bank or ledge at a set distance instead of crossing back and forth over it.
- Mark targets on the image. Most units let you select a spot on the side image and save it, which places the waypoint on the object rather than on the boat’s track.
- Confirm before you fish. Idle back over the waypoint and check it with down imaging and 2D sonar for height, fish and bait.
Image quality depends heavily on the installation, because side imaging needs a level transducer with a clear view to both sides. See transducer mounting options before you drill any holes.
When side imaging finds more fish, and when it does not
Side imaging pays off on big reservoirs, open flats, long ledges and rivers, where many of the best spots are small, scattered and away from the obvious structure. It also helps in shallow, clear water where a boat passing overhead can scatter fish.
It adds less on small ponds, narrow creeks and in thick vegetation, where you can see the cover or simply cast to it. Matted surface grass and rough water also degrade the picture. In those places, the money may be better spent on a larger screen or better maps.
Do you need both?
Many mid-range transducers combine 2D CHIRP, down imaging and side imaging in one housing, so the choice is often about the transducer and the mount rather than the display. Kayak anglers and anglers on small waters often get most of the benefit from CHIRP and down imaging alone. Boat anglers on larger lakes usually find side imaging the more useful upgrade, especially when they save what they find on a good lake map for later trips.
Bottom line
Down imaging tells you what is under you; side imaging tells you where to go. Use side imaging to search and mark spots, use down imaging and 2D sonar to confirm cover and fish, and pick the frequency by its trade-off: lower for range, higher for detail.
FAQ
Does side imaging work in shallow water?
Yes, and that is one of its strengths, because it shows fish and cover to the side without driving over them. Use a higher frequency and a shorter range for the sharpest images.
Can I use side imaging from a kayak?
Yes, if the transducer can be mounted level with a clear view to both sides, such as in a scupper or on a side arm. Keep the kayak moving straight and steady while you scan.
Why don’t fish show as arches on down imaging?
Imaging uses a very thin beam, so fish usually show as dots or short dashes rather than arches. Run 2D sonar next to down imaging if you want arches as well.
Does side imaging work while the boat is stopped?
Not well. The image is built from the boat’s movement, so a stationary boat draws a smeared strip of the same patch of bottom over and over.
