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depth of field questions

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depth of field questions

Postby nate on Tue Jun 01, 2010 2:08 pm

Field of view tends to be brought up frequently, but I don't hear much about depth of field. I imagine this is largely because FOV can be quantified and DOF maybe can't.

Can I get some input as too how important a consideration DOF should be?

I've heard that lower magnification usually means better DOF and that porro prisms tend to be better in DOF than roof prism (assuming similar quality). Is this true? Are there other general indicators as to which binoculars will have better DOF?

Re: depth of field questions

Postby Jne_K on Wed Jun 02, 2010 7:59 am


Depth of field is much, much more important in photography than it is in binoculars. In binoculars, it is almost a non-issue, by comparison. In fact, I would not lose any sleep over it.

In a binocular, we also use the phrase a bit differently than in photography, so be careful to make the distinction as to the equipment used. To keep it simple, a binocular that has good depth of field is a binocular that will require you to change focus less at close range than a binocular with average depth of field. This can be a factor for close in work, like birding, where birds are constantly changing position and you need to change focus, frequently, to keep up. Yes, porros do have better depth of field, as a rule, so you may not have to refocus as frequently, but that focusing advantage is often lost, since many porros focus less smoothly and focus slower than a good roof. Keep in mind that you still need to change focus with a porro, too. No such thing as a bino that you do not need to refocus at close range when the subject moves a lot. Personally, as a birder, I regard speed and ease of focus to be more important than the little bit you gain with a porro in terms of depth of field and that typically means a roof.

Once you reach the infinity point for focus on a binocular and that is usually 100-150 yards, more or less, for a typical binocular, depth of field becomes a moot point. Higher magnification does flatten the field, to some extent, bringing in the infinity focus point a bit closer than a lower power bino, but this is seldom any real advantage in my experience.
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