Birding spotting scopes can cost upwards of $6000 so it's important to know what you're investing in before you drop that kind of money. The major factor that determines cost is the lens quality and design. Other features also come into play such as being fog resistant, water resistant, and shock resistant. However, the lens is surely the most important factor.

Birding scopes are for looking at birds from afar, like eagles on a cliff, or hawks by the sea. You want to be able to see the birds' details that your binoculars will not provide. Lens quality will allow you to see the birds very brightly and vividly. Zoom and magnification is what allows spotting scopes to give you so much zoom and detail, all while being comfortably far away.

When birdwatching with your gear, you will be exposed to the elements like rain, wind, dirt and heat. Without shelter, you will need a scope that is waterproof. Also, you want rubber padding or armor because your scope will inevitably be bumped at some point in time. This rubber protection will protect your gear from the collisions and dings and dents. If you spend $1000 or more on Kowa spotting scopes or any other brand for that matter, you surely want your investment as protected as possible.

Based on how you will be using your scope (what kind of conditions, frequency, etc), you can use this information to make the best decision. Talk to friends who have gone through the same decision making process and see what they have to say. This way you will have peace of mind knowing that you took the time to do the research and made the best purchase for you.