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Binocular length (1 Viewer)

Just read that long focal length telescopes have more depth of field! Guess stopping down to increase dof may also work for binoculars... Not sure how much effect the stopping down or increasing focal length by 25% has though, because in telescopes the increases in length are much larger....:smoke:

Just noticed this post. My answer above applies to telescopes as well. If the telescope's exit pupil is larger than the eye's pupil magnification is the one and only significant factor for DOF. However, if the telescope objective is stopped down so that the exit pupil is smaller than the eye's pupil the DOF will increase, not because the focal ratio of the telescope is higher, but because the focal ratio of the the eye is now higher.

Henry
 
So really longer length in a binocular does not necessarily mean better optical performance. It is dependent on the optical design. As Henry says because of optical design the SV probably has a longer focal length than the SF. Ergonomically, I prefer a shorter binocular.

“Necessarily?” NO. Traditionally? YES.

Shorter focal ratio systems CAN be equal to longer ones. However, it usually requires MORE EXOTIC glass types (read: $$), at least one ASPHERIC ELEMENT (read: $$), MORE ELEMENTS (read: extra weight).

Those unfamiliar with optical engineering have a proclivity to think that you can correct for optical aberrations onesie-twosie. ‘Tain’t so. You might correct one aberration to a desired level at the expense of increasing another a little and driving two others into the realm of the unreasonable. An engineer tries to design using his “degrees of freedom” to come up with a design that will meet the requirements of the MAJORITY of potential buyers.

This is also true of conceptual matters. I designed a Houghton telescope in which all photo-visual wavelengths would fit into the Airy Disc like a pea in the center of the platter. The contrast-destroying central obstruction was about 40%. By simply changing the designated stop from the primary mirror to the secondary mirror, I reduced the central obstruction to 30%. By so doing, the contrast was MUCH better. However, spots and OPDs looked like they had been concocted by a third grader.

Physics can be a harsh taskmaster. :cat:

Bill
 
Don't know about DOF but I was able to measure distances of a mile, maybe more, with the 317mm Dall Kirkham, 4650mm focal length, just by the focus position of the eyepiece compared to the stars.
So I don't think the DOF was that great, although it could be.
I don't think the 317mm aperture was stopped down at high magnification.

I suppose it was similar to a 317mm base rangefinder with high magnification, although I haven't done calculations to compare.

I also had an approximately 6ft rangefinder possibly Barr and Stroud, which measured miles I think. I can't remember the maximum accurate range or the accuracy.

P.S.
Apparently the Americans used stereoscopic rangefinders and the British Barr and Stroud were coincidence rangefinders.
The stereoscopic and coincidence acuities were about equal in tests.
4.5m American and 3m British instruments.
Ranges 4,000 yards to 12,000 yards approx.

Laser rangefinders are used nowadays but can give away the observer's position.

I suppose the DOF in binoculars and telescopes depends on the observer's accommodation and acuity?
 
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