The best by a long way in very close focus distance are the Alpen Apex 8x32, the Backcountry 8x25 Pocket Roof Prism Binocular by Columbia and the Eagle Optics Ranger SRT 8x32 Binocular (compact binoculars), as well as the Zumell Signature 10x42 and Hawke Endurance Close Focus 10x42, both normal size binoculars. An object as close as less than 4 feet (1.2 meters) can be focused upon by these binoculars, which is astonishing and makes them capable of opening the world of insects to the viewer.
If using superlative words to describe close focus ability of 1 meter, how are you going to describe what the Pentax Papilio can do, which can focus as close as 18 inches(46 cm)?
The problem with super close focusing:
All binoculars have two barrels with one objective lens and one eyepiece in each. Each telescope delivers its own image to the viewer. This means that the viewer actually receives two different images through the eyepieces. As long as the viewer is focusing on an object in the distance, he perceives these two images as one. But integrating the two images into one becomes more difficult the closer the object he is viewing. Eventually it is no more possible. There is a critical distance at which the two images from the telescopes overlap naturally. This is where most binoculars have their close focus limit. As said above, this could be a close as 1 meter. On the downside it has to be mentioned that the two images are usually not completely integrated into one perfect image.
How has Pentax approached the problem?
Pentax knew they had to think out of the box to solve this problem and their answer was CLOSE : Convergent Lens Optical System Engineering. Whereas the eyepieces are still where one expects them, the objective lenses at the front are placed in a housing which cannot be adjusted along with the eyepieces. Adjusting the barrels to fit your eyes has no impact on the position of the objective lenses, as in the case of all other binoculars.
For focusing you use the focus knob on top of the instrument as in all binoculars. Focusing is done by moving the lenses closer or further apart from one another and not, as in the case of other binoculars, by moving the lenses closer or further away from the eyes of the viewer.
Since the objective lenses are placed inside a solid housing, they start moving towards one another when the viewer focuses on an object. Using an ordinary pair of binoculars, focus on an object at a distance no problem; now get closer; still no problem; now real close by and you'll see that the two images do not overlap completely. Then do that with the Pentax Papilio; no problem at all! Since the two lenses converge on each other, the two images overlap completely up to as close as 18 inches. So you can still see the object with both eyes as one integrated image and that happens without any eyestrain!
As you focus closer and closer, each eye's line of sight converges with the other's, so you're constantly looking at the same object with both eyes.
The Pentax Papilio is a reverse porro; it is a compact binocular (4 inches x 4.5 inches, objective lenses 21 mm) and lightweight (10.5 ounches).
This binocular is available in either a 6.5 or a 8.5 magnification, both with objective lenses of 21 mm.
This binocular was developed for very close viewing, as explained above and even indicated in the name ('papilio' = 'butterfly' In this regard it is unrivalled. The only limitation it has as far as viewing objects close and far away is the size of the apertures (21 mm), but that applies to all compact binoculars in any case.