Guide to DSLR Cameras and Settings | Exposure Triangle Basics

If you are shopping for your first serious camera, this guide to DSLR cameras and settings explains what makes them different, how the three core exposure controls work together, and what to do the day the box arrives.

What Makes a DSLR a DSLR?

A DSLR combines interchangeable lenses with a mirror-and-prism viewfinder. Light enters the lens, bounces off a mirror, and reaches your eye through the optical viewfinder, so you see exactly what the lens sees. When you press the shutter, the mirror flips up, and light hits the sensor to record the photo.

Most consumer DSLRs use one of two sensor sizes:

• APS-C (DX): roughly 24 × 16 mm — compact bodies, lower cost, and a 1.5x crop factor on lenses.
• Full-frame (FX): roughly 36 × 24 mm — the classic 35mm size, with better low-light performance and wider field of view.

Both are still sold in 2026. Nikon’s current lineup, for example, includes the full-frame D780 and D850 alongside the APS-C D7500 and D3500.

How the Exposure Triangle Works

Every DSLR photo is shaped by three controls: aperture, shutter speed, and ISO. Learning to balance them is the whole game.

Aperture is the lens opening. Low f-numbers like f/1.8 or f/2.8 let in lots of light and blur the background behind your subject. High f-numbers like f/11 bring more of the scene into focus, from foreground to horizon. Shutter speed controls motion. Fast speeds like 1/1000 sec freeze action; slow speeds let moving subjects blur and demand steady support. ISO is the sensor’s sensitivity. Low values like 100 give clean images in bright light; high values like 3200 help in dim scenes but add visible noise.

Every mode on your camera is really a strategy for these three variables:

• Auto picks all three for you — perfect for your first day.
• Aperture Priority (A on Nikon, Av on Canon) — you set aperture, and the camera picks shutter speed. This is the best mode for learning creative depth of field.
• Shutter Priority (S on Nikon, Tv on Canon) — you set shutter speed to freeze or blur action.
• Manual (M) — you control all three. Move to this once you understand how they interact.

When the exposure looks wrong, change one setting at a time, retest, and adjust slightly before changing another. Common beginner starting points: f/2.8 for portraits, f/8 to f/11 for landscapes, f/5.6 for general walkaround shooting, ISO 100–200 in bright light, and ISO 400–800 in dim light.

Setting Up a New DSLR

Unboxing a new body is straightforward. Insert a charged battery and an SD memory card, attach the lens by lining up the mount marks and turning until it clicks, then set the mode dial to Auto. Your camera’s manual — Nikon publishes detailed PDF manuals for each body — is the final word on battery orientation, card compatibility, and button layout.

The fastest way to improve is to leave Auto quickly. Switch to Aperture Priority and practice controlling depth of field. Keep your focus mode set to autofocus while you learn; refine manually later. The most common beginners’ mistakes are staying in Auto forever, confusing Aperture Priority with Shutter Priority, pushing ISO too high out of habit, and using a shutter speed too slow to freeze action.

Which DSLR Should You Buy?

Choose the body that matches your needs and budget. Nikon’s current consumer DSLR lineup shows how the specs compare.

The D780 and D850 are heavier, pricier full-frame bodies built for low light and high detail; the D7500 and D3500 are lighter APS-C options that still shoot 4K UHD video (the D3500 tops out at Full HD 1080p). Prices change quickly, so confirm current costs before buying.

For most new shooters, an APS-C model is the smart first camera: smaller, cheaper, and more than capable of teaching every setting in this guide. If you are ready to compare the best entry-level DSLR cameras, that roundup covers the top picks side by side. And if you are weighing DSLR versus mirrorless, know that DSLRs remain excellent buys in 2026 — optical viewfinders, long battery life, and a huge used-lens market keep them very much alive. Nikon’s official DSLR lineup page is the authoritative source for current model specs.