A-t-on vraiment besoin d’une longue-vue à grand diamètre ?

Do we really need big scopes? Here’s the question asked by the american website Betterviewdesired.com. The last large models with 77-80 mm of glass and/or fluorite, a tube to hold the 480 or so millimeters of focal length, prisms big enough to contain and turn the light cone, eyepieces to provide sufficient power, field, and eye relief—it all adds up to a large and often very heavy package. But a good deal of the performance gain most people see in going from a 60 mm to a larger scope is due, not to the larger size, but to better objective and eyepiece design. Most of conventional prismatic 80 mm and smaller scopes reached their maximum resolution at about 60 x power. After that, the image got bigger, but it did not show any more detail.
In most birding situations the best of the 60 mm scopes currently on the market will give you all the performance you need, and all the performance you can actually use, at anything up to 60 X. If you want to go a step up in optical performance from there, you are going to have to look at unconventional large mirror scopes.