Call me a sweet old fashioned guy but for 50 years i have owned only porro prism binoculars. My reasons were the price and very importantly the better ( to my eye ) depth of field. Researching the internet has confirmed my beliefs that the porros have a better field of view. However have things changed with all the improvements made to contemporary roof prisms? I am contemplating buying into my first pair of roof prisms but only if the depth of field is at least equal to the porros. The second part of my dilemma is can i buy the kind of equal depth of field quality for $300. plus minus a few dollars ?
This subject comes up often but I think that most people have come around to the conclusion that all binoculars of the same power have the same depth of field. Lower power binoculars have deeper fields of view in front of and behind the bird you are looking at than high ones do. Often binoculars which have fast focusing ratios will appear to not have the same depth of field as those with slower focusing ratios because it is easier to "fine tune" your focus with the latter without "overshooting" or "undershooting" the bird you are looking at.
What I think you will notice after switching to roof prism will be that the appearance of the bird you are looking at is larger than it would have appeared in a porro of the same power.
Bob
cappi,
be sure not to confuse depth of field with 3D-effect.
The depth of field, which by the way depends on the individual user and light conditions, tells how far behind and how far in front of the point of focus the sharpness still is fine.
A monocular has depth of field, but no 3D effect.
But curiously, a spotting scope or monocular can show some kind of odd 3D effect:
I've discovered that when looking at a bird through a scope at decent distance, the far situated background will seem to change its position relative to the bird if the observer moves his head sidewise. Such behaviour can't happen through binoculars because the distance between the oculars and their relative position to the eyes won't allow the freedom of sidewise head movements.
Real 3D effect is achieved through the lateral displacement of the binocular's barrels and the accompanying parallax of the two images. But 3D perception/stereoopsis is something that takes place in the visual cortex of the brain and not in the binoculars optical paths.
The greater parallax of porro (porri?) binoculars gives the user stronger cues to 3D perception, as long as they are not used at too short or too long distances.
//L
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