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Quick Answer
Down imaging shows photo-like pictures of rocks, trees and bottom structure directly below the boat. Side imaging shows the same kind of picture out to each side, so it covers far more water and is best for finding structure. Down imaging is better for studying exactly what is under you. Many side imaging transducers include down imaging too, such as Humminbird's MEGA Side Imaging models, and you still need traditional 2D or CHIRP sonar to see fish as arches.
Who This Guide Is For
This guide helps you if you are choosing between an imaging transducer and a standard 2D transducer, or deciding whether side imaging is worth it for the water you fish.
It does not cover forward-facing sonar or 360 sonar, which work differently and have their own guides.
What Each One Shows
Lowrance describes down imaging as photo-like images of structure directly beneath the boat, and side imaging as views up to 600 ft to each side, which it says covers more water in less time. Traditional and CHIRP sonar show fish as arches or lines, along with the bottom.
Each brand uses its own names:
| Brand | Down imaging | Side imaging |
|---|---|---|
| Garmin | ClearVü | SideVü |
| Humminbird | Down Imaging, MEGA Down Imaging | Side Imaging, MEGA Side Imaging |
| Lowrance | DownScan Imaging | SideScan |
Five Things to Compare
| What to compare | Down imaging | Side imaging |
|---|---|---|
| Where it looks | Directly below the boat | Out to the left and right of the boat |
| Best for | Studying structure under you, seeing what you are fishing over | Searching large areas quickly for structure, edges and cover |
| Range at 455 kHz (Humminbird) | Depth of 125 to 400 ft, depending on the transducer | Range of 480 to 800 ft side to side, depending on the transducer |
| Range at 800 kHz (Humminbird) | Depth of up to 125 ft | Range of up to 250 ft side to side |
| Coverage angle (Humminbird) | 45° at 800 kHz, 75° at 455 kHz | Two beams, 55° to 86° each depending on frequency and model |
Garmin lists 260, 455 and 800 kHz for both ClearVü and SideVü on its ECHOMAP UHD sonar models, and Lowrance uses 455 and 800 kHz for both DownScan and SideScan. Real range always depends on the transducer, water conditions and bottom type.
How to Decide Which You Need
- Think about how you search. If you spend time covering water to find structure, side imaging saves time. If you fish known spots, down imaging may be enough.
- Check your water depth. Deep water favours lower imaging frequencies such as 455 kHz. Humminbird lists 800 kHz down imaging to 125 ft.
- Check what your fish finder supports. An imaging transducer only works on a unit that supports imaging. Check it in our compatibility checker.
- Check your transducer mount. Side imaging needs a clear view to both sides. Our guide to transducer mount types covers placement.
- Remember the 2D view. Plan to keep traditional or CHIRP sonar on screen for fish arches, alongside the imaging view.
- Compare the full transducer specs for range, frequency and coverage angle before you buy.
Worked example
Working out how much bottom down imaging covers
You fish in about 30 ft of water and want to know how wide a strip of bottom a down imaging beam covers. Humminbird lists down imaging coverage of 75° at 455 kHz and 45° at 800 kHz.
- Use half the angle. The beam spreads evenly either side of straight down, so use 37.5° for a 75° beam.
- Work out the width. Width is about 2 × depth × tan(half angle).
- At 455 kHz. 2 × 30 ft × tan(37.5°) = 2 × 30 × 0.767, which is about 46 ft of bottom.
- At 800 kHz. 2 × 30 ft × tan(22.5°) = 2 × 30 × 0.414, which is about 25 ft of bottom.
- Result. At 30 ft, 455 kHz shows roughly a 46 ft strip and 800 kHz a 25 ft strip with sharper detail. Side imaging at the same spot can show hundreds of feet across, which is why it is used for searching.
These are geometric estimates. Humminbird measures its angles at -10 dB, and real coverage changes with the bottom, the water and your settings.
When Imaging Is Not the Right Choice
- You mainly want to see fish. Imaging is designed to show structure. Traditional and CHIRP sonar show fish as arches, so a good 2D transducer may matter more.
- Your fish finder does not support it. Some entry-level units have no imaging, and an imaging transducer will not add it.
- You fish very deep water. Humminbird lists down imaging depth limits between 75 and 400 ft depending on frequency and transducer, so check your model's figures.
- You fish mainly at the bow. A transom imaging transducer shows the water behind the boat. A trolling motor imaging transducer may suit you better.
Action Checklist
This page contains no affiliate links. It was researched from the manufacturer documents listed below, and the products were not tested by us. We will recheck it by May 2027, or sooner if Garmin, Humminbird or Lowrance change their imaging specifications.
Common Questions
What is the difference between side imaging and down imaging?
Down imaging shows photo-like images of structure directly below the boat. Side imaging shows the same kind of image out to each side of the boat, covering a much wider strip of water.
What are the brand names for down and side imaging?
Garmin calls them ClearVü and SideVü, Lowrance calls them DownScan and SideScan, and Humminbird calls them Down Imaging and Side Imaging, with MEGA versions.
Which frequency should I use?
Lower imaging frequencies such as 455 kHz reach further and deeper, while higher frequencies such as 800 kHz show sharper detail over a shorter range. Lowrance says 800 kHz is sharpest in shallower water and 455 kHz gives better overall image quality and depth.
Do I still need traditional 2D sonar?
Yes, for most fishing. Lowrance explains that traditional and CHIRP sonar show fish as arches, while down imaging is designed to show structure, which is why many units show both views side by side.
How far can side imaging see?
It depends on the transducer and frequency. Humminbird lists up to 800 ft side to side at 455 kHz on some transducers, and Lowrance says SideScan can show up to 600 ft to each side of the boat.
Sources
- Humminbird Help Center, Side Imaging Transducers, Operating Frequencies and Areas of Coverage
- Humminbird Help Center, Understanding Transducer Frequencies and Cone Angles
- Garmin ECHOMAP UHD owner's manual, Sonar Models Specifications
- Lowrance, Sonar Basics
Manufacturers change part numbers and firmware support. Confirm with the manufacturer before you buy.