5 Best Budget Binoculars Review for Birding Now

Have you ever spotted a flash of color in the trees and wished you could see that beautiful bird up close? Bird watching is an amazing hobby, but sometimes great binoculars cost a lot of money. It feels frustrating when you want to enjoy nature better, but your wallet says no. Finding good, affordable binoculars can feel like searching for a needle in a haystack.

Many beginners worry that cheap binoculars will offer blurry views or break quickly. You do not need to spend a fortune to enjoy the details of a cardinal’s crest or an eagle soaring overhead. This guide cuts through the confusion. We will show you exactly what features matter most in budget-friendly models.

By the end of this post, you will know how to spot the best value. We will share top picks that deliver crisp images without emptying your bank account. Get ready to upgrade your birding experience today!

Top Budget Binoculars For Bird Watching Recommendations

No. 1
Occer 12x25 Compact Binoculars for Adults and Kids, Large Eyepiece Waterproof Binocular with Low Light Vision,High Powered Easy Focus Binoculars for Bird Watching,Outdoor Hunting,Travel,Sightseeing
  • 【HIGH-POWERED LARGE EYEPIECE BINOCULARS】 This binoculars for adults has 12x magnification, 25mm objective lens and wide field of view, 273ft/1000yds, letting you look farther and see wider. Coating with FMC Broadband coating and premium BAK4 prism, it ensure imaging verisimilar.
  • 【ADJUSTABLE EYE CUPS FIT EYEGLASS WEARERS OR NOT】The binocs can be pull down the rubber eyepieces and more fit the glasses wearer, getting close to lens and see easily. The long eye relief combined with large eyepiece give you a comfortable viewing while wearing sunglasses or eye glasses. For those who do not wear glasses, will gain more focused slight and feel more easeful through rising eye cups. The compact binoculars has 15mm large eyepieces, can see more clear image than other travel binoculars.
  • 【FMC BROADBAND COATING TECHNOLOGY】The lightweight cruise binoculars is cover with BAK4 prism texture. The objective lens use optical FMC multilayer broadband green film, and the eyepiece-optical is made of blue FMC coating. All design ensure to provide a good image and make you have a amazing experience.
  • 【PORTABLE, COMPACT AND SMALL BINOCULARS DESIGN】 One hand can be mastered when you use the birding watching binoculars for opera,bird watching camping, traveling,wildlife watching,football games,cruise or other outside activity, the low light night vision goggles(Not for completely dark night) is more convenient for using and carrying.
  • 【LIFE WATERPROOF, COMFORTABLE TOUCH】 The kids binoculars are made of ABS plastic and it also come with a cruise binocular strap, you can use this item in different situations. And rubber armor is made for secure grip.The pocket size binoculars is not only suitable for men and women,but also suitable for kids.It is wonderful to give your Father or Children.
No. 2
15x52 HD Binoculars for Adults High Powered with Upgraded Phone Adapter - Large View Binoculars with Clear Low Light Vision - Lightweight Waterproof Binocular for Bird Watching Travel Hunting Cruise
  • 🐧【𝟏𝟓𝐱 𝐇𝐢𝐠𝐡-𝐏𝐨𝐰𝐞𝐫𝐞𝐝 𝐁𝐢𝐧𝐨𝐜𝐮𝐥𝐚𝐫𝐬: 𝐃𝐢𝐬𝐜𝐨𝐯𝐞𝐫 𝐍𝐚𝐭𝐮𝐫𝐞'𝐬 𝐒𝐦𝐚𝐥𝐥𝐞𝐬𝐭 𝐃𝐞𝐭𝐚𝐢𝐥𝐬】Elevate your viewing experience with these 15x high-powered binoculars designed for adults. Crafted for observing extremely long distances, these professional high-powered binoculars provide a razor-sharp view of the smallest details even at longer ranges. Unlock the smallest secrets of nature and immerse yourself in crisp, razor-sharp visuals that traditional 12x magnification binoculars cannot match.
  • 🐧【𝟐𝟐𝐦𝐦 𝐋𝐚𝐫𝐠𝐞 𝐄𝐲𝐞𝐩𝐢𝐞𝐜𝐞 𝐁𝐢𝐧𝐨𝐜𝐮𝐥𝐚𝐫𝐬: 𝐋𝐚𝐫𝐠𝐞𝐫 𝐈𝐦𝐚𝐠𝐞, 𝐂𝐥𝐞𝐚𝐫𝐞𝐫 𝐃𝐞𝐭𝐚𝐢𝐥𝐬】Thanks to the expanded 22mm large eyepiece performance, you can enjoy exceptionally detailed insights into the natural world. These binoculars provide a wider field of view, 1.5 times larger than the image size of 16mm eyepieces (e.g., ordinary 10x42, 12x42 binoculars) and 1.2 times that of 20mm eyepieces (e.g., 12x50 binoculars). Large eyepiece binoculars fully utilize the 15x magnification, delivering a larger image and ensuring clearer details.
  • 🐧【𝟐𝟎𝟐𝟔 𝐔𝐩𝐠𝐫𝐚𝐝𝐞𝐝 𝐏𝐡𝐨𝐧𝐞 𝐀𝐝𝐚𝐩𝐭𝐞𝐫 𝐟𝐨𝐫 𝐁𝐢𝐧𝐨𝐜𝐮𝐥𝐚𝐫 𝐏𝐡𝐨𝐭𝐨𝐠𝐫𝐚𝐩𝐡𝐲】The universal upgraded smartphone adapter enables you to capture outstanding photos. It's easy to set up and align quickly. The soft anti-slip rubber on the surface, along with a sturdier structural design and screw locks, firmly secure your phone, ensuring stable and clear images when taking photos or videos. This adapter is suitable for all kinds of smartphones, with or without phone cases.
  • 🐧【𝐂𝐥𝐞𝐚𝐫 𝐋𝐨𝐰-𝐋𝐢𝐠𝐡𝐭 𝐕𝐢𝐬𝐢𝐨𝐧 𝐁𝐢𝐧𝐨𝐜𝐮𝐥𝐚𝐫𝐬 𝐟𝐨𝐫 𝐇𝐮𝐧𝐭𝐢𝐧𝐠】The 15x52 model allows you to experience an entirely new dimension of hunting in low-light conditions. Equipped with a 52mm objective lens, 18mm BAK4 dielectric-coated prisms, and high-transmission specialized glass, these binoculars deliver the best possible performance in low-light scenarios for observation. Overcast days, dense tree canopies, daybreak, and the last light of the day are the specific situations in which these binoculars were designed to excel.
  • 🐧【𝐇𝐢𝐠𝐡-𝐂𝐨𝐧𝐭𝐫𝐚𝐬𝐭 𝐚𝐧𝐝 𝐓𝐫𝐮𝐞-𝐭𝐨-𝐋𝐢𝐟𝐞 𝐁𝐢𝐧𝐨𝐜𝐮𝐥𝐚𝐫𝐬 𝐟𝐨𝐫 𝐁𝐢𝐫𝐝 𝐖𝐚𝐭𝐜𝐡𝐢𝐧𝐠】Experience high color fidelity binoculars for bird watching that ensure no details are lost, even in the deepest twilight. These advanced birding binoculars are equipped with fully multi-coated lenses and high-resolution phase-corrected BAK4 roof prisms, guaranteeing high-contrast images with incredible color fidelity. You can discern every detail for quick and easy identification in any bird-watching scenario you encounter.
No. 3
12x42 HD Binoculars for Adults High Powered with Phone Adapter and Tripod, Super Bright BAK4 Prism Waterproof Binoculars for Bird Watching Hunting Hiking Safari Travel Sports
  • High Definition Binoculars for Bird Watching, Hunting, Stargazing, Traveling & Whale Watching: Adasion 12x42 high powered binoculars provide 12X magnification and 18mm eyepieces, feature a 367/1000yds large field of view, and delivers large and clear details
  • Vivid, Clear & Bright View Even in Low-Light: 42mm large objective lens, collect more lights, deliver brighter view; BAK4 prism and FMC are usually applied in professional binoculars, increasing light transmittance and providing good color reproduction. All of these provide premium image quality
  • Powerful Camera Function, The Ideal Choice for Gifts: 2022 newly upgraded universal phone adapter fits all smartphones; 360° swivel and 2.2" extendable tripod w/ adapter ensures stable photo shooting. The ideal gift for Father's Day and Children's Day. Ideal gift for outdoor. The ideal binoculars for boys and girls
  • Light Weighted and Portable, Perfect for the Outdoors: Ideal choice for outdoor activities with only 1.25 lbs weight and crossbody case. Non-slip rubber and IP55 rain & fog resistance are suitable for most outdoor occasions
  • Simple to Use, Comfortable Experience: Twist the eyecups up and down to see the world with or without glasses - eye relief range 13.6mm - 19.6mm. Adjust the center focus wheel to easily fit your eyes, and the diopter (located on the right eyepiece) balances left and right eye parallax
No. 4
Adorrgon 12x42 HD Binoculars for Adults High Powered with Phone Adapter, Tripod and Tripod Adapter - Large View Binoculars with Clear Low Light Vision - Binocular for Bird Watching Cruise Travel
  • 【Powerful 12x42 Binoculars, but Lightweight Enough, only 1.1 pounds】 Adorrgon 12x42mm binoculars deliver 367ft/1000yds large field of view. Capable of delivering a clear face from more than 650 feet away. Perfect for bird watching, hunting, sports events.
  • 【Clear Low Light Vision】Advanced Fully Multi-coated Binoculars with large 16.5mm BAK4 prism lens binoculars deliver brighter vision in weak light condition (e.g. Twilight). Perfect for Hunting or Concerts at night.
  • 【18.5mm Large Eyepiece & HD Vision , Larger Image, Brighter View】 2.25 times the image size of 14mm eyepiece (e.g. 10x25/10x21 binoculars), 1.28 times of 16mm eyepiece (e.g. 12x25 binoculars). Large eyepiece binoculars make full use of 12x magnification, deliver larger and brighter image, ensure clearer details.
  • 【2026 Upgraded Universal Phone Adapter, Sturdy and Easy to set up】 Soft anti-slip rubber and sturdy structure design ensure stable camera image when photographing. Suitable for all kinds of smartphone with or without phone case, including but not limited to iPhone, Samsung, Sony, Google, LG, Motorola, HTC, etc.
  • 【360° Rotatable and Sturdy Tabletop Tripod, Photographing without Shaking】 Rotatable designed tripod ensures 360° photographing. Thicker and sturdy tripod leg, Non-slip rubber feet, enable you to shoot clearer and brighter pictures without shaking. Capture the wonderful moments and share with your friends.
No. 5
20x50 High Powered Binoculars for Adults, Waterproof Compact Binoculars with Low Light Vision for Bird Watching Hunting Camping Travel Cruise Hiking Sports Stargazing, Christmas Birthday Gifts for Men
  • UPGRADED HIGH-POWER BINOCULARS​ - These premium binoculars feature a high-magnification 20x zoom eyepiece and offer a 168-yard field of view at 1000 yards. This allows you to observe and focus on intricate details of distant targets up to 1000 yards away, delivering exceptionally broad and clear long-distance vision. Ideal for adults engaged in bird watching, hunting, camping, climbing, hiking, safari, travel, opera, concerts, sports events, and stargazing. They are essential gear for camping, hunting, travel, and cruises.
  • ​OPTIMIZED EYEPIECE DESIGN​ - The 26mm eyepiece is ergonomically designed to comfortably fit the eye structure of users, providing a wider and clearer field of view for birdwatching and other outdoor activities. The large eyepiece design helps maintain visual stability, reducing the risk of dizziness and eye fatigue during prolonged use. These binoculars make an ideal gift for men, dads, Father’s Day, Christmas, and birthdays.
  • ​SUPERIOR IMAGE CLARITY​ - Multilayer-coated aspherical lens elements ensure superior light transmission with minimal distortion, enhancing image brightness, contrast, and overall quality. The BAK4 Porro prism, with its high refractive index, achieves 99.8% light transmission for improved color accuracy. The green FMC (Full Multi-Coating) anti-reflective coating on the objective lens reduces reflected light, further boosting light transmission, image brightness, and sharpness for an exceptional viewing experience.
  • ​EASY AND PRECISE FOCUSING​ - These binoculars are designed for effortless operation: simply adjust the barrels to align with your eyes, then rotate the sensitive, non-slip center focus wheel with one finger to achieve a sharp, single image without double vision. The focus wheel is covered with soft rubber for comfortable, long-term use without finger fatigue.
  • ​RUGGED AND WATERPROOF CONSTRUCTION​ - The binoculars feature a daily waterproof body with a rubber coating that provides impact resistance and a firm, comfortable grip. Built with high-quality materials, they are suitable for various outdoor conditions, including harsh environments (note: please do not immerse the binoculars in water). The unique non-slip ergonomic handles on both sides are made of eco-friendly rubber with a textured surface, ensuring a secure and comfortable hold that prevents slipping.
No. 6
Hontry Binoculars for Adults and Kids, 10x25 Compact Binoculars for Bird Watching, Theater and Concerts, Hunting and Sport Games
  • An ideal choice magnification: A 10x magnification strikes the balance between zooming in on your target and maintaining a steady image, making it an ideal choice for everyday use.
  • Equipped with Bak-4 prisms: These prisms deliver images with 3D depth and rich detail. Even under low-light conditions, you’ll still enjoy bright, sharp views.
  • Compact design: About the size of your palm and weighing only 0.6 pounds - makes it easy to carry around wherever you go. With these features, your binoculars become a reliable companion for everyday adventures rather than a tool reserved only for special occasions.
  • Wide range IPD: With an adjustable interpupillary distance ranging from 60mm to 75mm, they comfortably fit both kids and most adults. This means everyone in the family can share the excitement of discovering new sights together.
  • Your one-stop solution: these binoculars absolutely for bird watching, cruising, hiking, and traveling, but they’re not just for the outdoors—catch every thrilling moment at sporting events, concerts, plays, and more. What's more? Don’t forget the simple pleasures: Keep them handy in the car glove box, use them during a layover at the airport, or explore your own backyard. Wherever your imagination takes you, Hontry binoculars are ready to follow.
No. 7
18x56 UHD Binoculars for Adults High Powered with Upgraded Phone Adapter, Wide Field of View Binoculars with Clear Low Light Vision, Lightweight Waterproof Binocular for Bird Watching Travel Cruise
  • 【𝟏𝟖𝐱 𝐇𝐢𝐠𝐡-𝐏𝐨𝐰𝐞𝐫𝐞𝐝 𝐁𝐢𝐧𝐨𝐜𝐮𝐥𝐚𝐫𝐬 – 𝐒𝐞𝐞 𝐅𝐚𝐫𝐭𝐡𝐞𝐫 𝐰𝐢𝐭𝐡 𝐂𝐥𝐞𝐚𝐫 𝐃𝐞𝐭𝐚𝐢𝐥】With powerful 18x magnification, these Ultra-High-Definition binoculars are designed for long-distance viewing. These high-performance binoculars deliver sharp, detailed images even at far distances, allowing you to see fine details with ease. Compared to standard 12x or 15x binoculars, they bring you closer with clearer, more immersive visuals—so you can enjoy every scene with exceptional clarity.
  • 【𝐂𝐥𝐞𝐚𝐫 𝐋𝐨𝐰 𝐋𝐢𝐠𝐡𝐭 𝐕𝐢𝐬𝐢𝐨𝐧 – 𝐁𝐫𝐢𝐠𝐡𝐭 & 𝐂𝐥𝐞𝐚𝐫 𝐢𝐧 𝐋𝐨𝐰 𝐋𝐢𝐠𝐡𝐭 𝐂𝐨𝐧𝐝𝐢𝐭𝐢𝐨𝐧𝐬】With a large 56mm objective lens and high-quality dielectric-coated BAK4 prisms, these binoculars deliver the brightest viewing images with outstanding resolution of the finest details even in low-light conditions. Whether you're out at dawn, dusk, on cloudy days, or viewing through dense forests, they let you see more details when light is limited—so every moment stays clear and within view.
  • 【𝐄𝐱𝐭𝐫𝐚-𝐖𝐢𝐝𝐞 𝐅𝐢𝐞𝐥𝐝 𝐨𝐟 𝐕𝐢𝐞𝐰 – 𝐄𝐚𝐬𝐢𝐥𝐲 𝐒𝐩𝐨𝐭 𝐚𝐧𝐝 𝐅𝐨𝐥𝐥𝐨𝐰 𝐌𝐨𝐯𝐢𝐧𝐠 𝐒𝐮𝐛𝐣𝐞𝐜𝐭𝐬】With a wide field of view, these binoculars let you see more at a glance, making it easier to quickly spot and follow moving subjects without losing sight. Ideal for bird watching and wildlife observation, they also enhance your experience when enjoying scenic views during travel or outdoor adventures, providing a more comfortable and immersive viewing experience.
  • 【𝐔𝐩𝐠𝐫𝐚𝐝𝐞𝐝 𝐔𝐧𝐢𝐯𝐞𝐫𝐬𝐚𝐥 𝐏𝐡𝐨𝐧𝐞 𝐀𝐝𝐚𝐩𝐭𝐞𝐫 – 𝐅𝐚𝐬𝐭𝐞𝐫 𝐀𝐥𝐢𝐠𝐧𝐦𝐞𝐧𝐭, 𝐌𝐨𝐫𝐞 𝐒𝐭𝐚𝐛𝐥𝐞 𝐒𝐡𝐨𝐨𝐭𝐢𝐧𝐠】Designed for quick and easy setup, this upgraded adapter lets you align your phone in seconds without complicated adjustments. Its secure, anti-slip design keeps your phone firmly in place, ensuring stable and clear photos and videos. Compatible with all kinds of smartphone, it makes capturing distant views easy—so you can capture and share every moment.
  • 【𝐋𝐢𝐠𝐡𝐭𝐰𝐞𝐢𝐠𝐡𝐭 & 𝐄𝐫𝐠𝐨𝐧𝐨𝐦𝐢𝐜 – 𝐖𝐚𝐭𝐞𝐫𝐩𝐫𝐨𝐨𝐟 𝐟𝐨𝐫 𝐎𝐮𝐭𝐝𝐨𝐨𝐫 𝐀𝐝𝐯𝐞𝐧𝐭𝐮𝐫𝐞𝐬】Lightweight and ergonomically designed, these binoculars provide comfortable all-day use. The waterproof and fogproof construction ensures reliable performance in changing weather conditions, while the non-slip rubber armor offers a secure grip even in wet environments. Ideal for birdwatching, hunting, hiking, safari, travel, and cruise—so you can explore with confidence and enjoy every moment.
No. 8
15x55 UHD Binoculars for Adults High Powered with Phone Adapter - Large View, BAK4 Prism, Waterproof, Lightweight for Bird Watching, Hunting, Cruise, Travel, Camping (Blue)
  • 【 High-Powered & Wide View】Enjoy 15x magnification with an 8° wide-angle field, delivering a crystal-clear 367ft/1000yds view. Perfect for bird watching, marine observation, and sports events. (Fixed 15x magnification – no zoom function)
  • 【 Exceptional Optics with BAK4 Prism】55mm objective lenses, fully multi-coated glass, and BAK4 prisms ensure maximum light transmission, vivid colors, and edge-to-edge sharpness—even in low light.
  • 【 All-Weather Durability】IPX7 waterproof, fogproof, and argon-purged for reliable performance in any climate. Rubber armor grip offers shock resistance and a secure hold.
  • 【 Versatile Outdoor Companion】Ideal for hiking, travel, stargazing, and cruises. Capture stunning views using the included phone adapter to take photos and videos through the lens.
  • 【 Comfortable for All Users】Adjustable twist-up eyecups with 13.6–19.6mm eye relief suit glasses wearers and non-glasses users alike. A great gift for adults, kids, and outdoor lovers.

The Ultimate Buying Guide: Budget Binoculars for Bird Watching

Bird watching is a wonderful hobby. You can enjoy nature from your backyard or on a big hike. Good binoculars help you see birds clearly without disturbing them. You do not need to spend a lot of money to get a great pair. This guide helps you choose the best budget binoculars for spotting feathers and wings.

Key Features to Look For

When shopping for budget birding binoculars, focus on these main specifications:

Magnification and Objective Lens Size (The Numbers)

  • Magnification (First Number): This tells you how much closer the bird appears. For birding, 8x is usually the best starting point. 8x means the bird looks eight times closer.
  • Objective Lens Diameter (Second Number): This is the size of the front lenses in millimeters (mm). A larger number lets in more light. For good all-around use, look for 10×42 or 8×42. The ’42’ is a good balance between light gathering and weight.

Field of View (FOV)

Field of View describes how wide an area you see through the binoculars at a certain distance (usually 1,000 yards). For birding, you need a wide FOV. Why? Birds move fast! A wide view helps you find and track fast-moving targets easily. Look for specs that state a high number (e.g., 390 ft @ 1000 yards).

Eye Relief

Eye relief is the distance your eye can be from the eyepiece and still see the full picture. If you wear glasses, you need long eye relief (15mm or more). This prevents your glasses from blocking your view.

Important Materials That Matter

The materials used affect how long your binoculars last and how clear the image is.

Prism Type

Binoculars use prisms to flip the image right-side up. There are two main types:

  • Roof Prisms: These are straight, sleek, and modern. They are usually lighter and more compact, which is great for hiking. Most quality budget binoculars use roof prisms.
  • Porro Prisms: These have a classic, wider shape. They can sometimes offer a deeper 3D look, but they are bulkier.

Lens Coatings

Good lens coatings are vital, even on a budget. Coatings reduce glare and improve light transmission, making the image brighter. Look for terms like “Fully Coated” or, even better, “Multi-Coated” (MC). Multi-coated lenses give you the best performance for the price.

Body Construction

Check the body material. Many budget models use durable plastic housing covered in rubber armor. The rubber protects the binoculars if you drop them. Make sure the body is **waterproof or water-resistant** and **fog-proof**. This usually means the inside is sealed with O-rings and filled with nitrogen or argon gas.

Factors That Improve or Reduce Quality

What makes a cheap pair feel expensive? It is often the small details.

Quality Factors (Good Signs)

  • Smooth Focus Wheel: The focus wheel should turn smoothly, not grind or feel loose. You need to make fast, precise adjustments when a bird lands nearby.
  • Diopter Adjustment: This small ring (usually on the right eyepiece) lets you fine-tune focus for differences between your two eyes. Ensure this moves easily but stays set once adjusted.

Quality Reducers (Warning Signs)

  • Soft Plastic Parts: If the focus wheel or eyecups feel very soft or flimsy, they might break quickly.
  • Muted Colors: If the image looks dull or yellowish, the lens coatings are probably poor. Good budget glass should look relatively bright and true to color.

User Experience and Use Cases

Your binoculars must match how you plan to use them.

Backyard Birding

If you watch birds mostly from a porch or window, weight is less important. You can focus more on image quality. An 8×42 model provides a great, steady view.

Hiking and Travel

If you carry them all day, weight matters a lot. Look for lighter 8×32 or 10×32 models. They are smaller and easier to swing up quickly when you spot movement in the trees.

Ease of Use

Always test the focus. Can you adjust the focus wheel quickly and accurately? If you struggle to get a sharp picture in the store, you will struggle even more when watching a fast-moving warbler!


10 FAQs About Budget Birding Binoculars

Q: What is the best magnification for a beginner budget birder?

A: Most experts suggest 8x magnification. It gives you a wide view and is easier to hold steady than higher powers like 10x or 12x.

Q: Do I really need waterproof binoculars?

A: Yes. Weather happens! Waterproofing protects the internal optics from rain, dew, and humidity, which stops fogging and damage.

Q: What does “close focus” mean?

A: Close focus is the nearest distance at which the binoculars can still focus clearly. For birding, especially if you watch butterflies or feeders up close, look for a close focus under 10 feet.

Q: Are cheap binoculars worth buying over none at all?

A: Absolutely. Even a decent budget pair will bring birds much closer than the naked eye. They significantly improve your viewing experience.

Q: How heavy is too heavy for birding?

A: For comfortable all-day carrying, try to keep the weight under 24 ounces (about 680 grams). Heavier models cause arm fatigue fast.

Q: What color should the lens coatings be?

A: Lens coatings often appear slightly colored, like a light green, purple, or amber tint. This color shows that light is being reflected efficiently, which is a good sign.

Q: Can I use binoculars designed for hunting for bird watching?

A: You can, but birding usually requires a wider field of view than hunting. Hunting binoculars often prioritize high magnification over a wide view.

Q: What is the main difference between 8×42 and 10×42?

A: The 10×42 magnifies more, but it shrinks your field of view and makes the image shake more easily because of the higher power.

Q: How do I clean the lenses on my new budget binoculars?

A: Use a specialized lens cleaning cloth or a blower bulb first to remove loose dust. Only use lens solution if necessary, wiping gently in a circular motion. Never use paper towels.

Q: If I have to pick one thing to spend slightly more money on, what should it be?

A: Spend slightly more on the **objective lens size (the second number)**. A 42mm lens will gather much more light than a 30mm lens, making a big difference on cloudy days or at dawn/dusk.