Quote:this Sky and Tel binocular article ...makes a brief mention of Mr. Bishops article I mentioned. The Observer's Handbook article is much more indepth but contained in the first link is the general idea of his "visibility factor". The second link is his enlarged visibility factor chart from the Sky and Tel article:
Quote: Many of the aberrations we see in binoculars affect edge performance. In fact, the aberrations described here all look somewhat different and affect different areas of the view.
WHAT DO ABERRATIONS LOOK LIKE
Generally, not all aberrations are seen on-axis. The on-axis image created by aberrations is as follows:
curvature not seen on-axis.
coma not seen on-axis.
If the stars seem never to focus to a fine point, but at best remain slightly bloated and are still circular, and it cannot be focused out it is probably spherical aberration.
If the star seems to not come into sharp focus it may be astigmatism. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint. Passing in and out of focus will show the out-of-focus image to flip orientation by 90°.
Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point. Sometimes seen as a small circular band of color areond a finely focused star point.
As for how you notice stars in the outer fov, the image created by aberrations is as follows:
If the star seems slightly bloated, but it can be refocused down to a finer point, then it is curvature, as Bill T described.
If the stars seem flared as wedges with the point towards the middle and the flared wedge toward the outer edge, them it is coma. It cannot be focused out.
If the stars seem slightly bloated but are still circular, and it cannot be focused out it is spherical aberration.
If the star seems slightly bloated and slightly elongated than it is astigmatism. Astigmatism will show elongated images off axis. If astigmatism is severe, then on-axis focused images will show a very small cross, never a fine pinpoint.
If you have both astigmatism and coma, the off axis images will look like comets with an oblong axis, or like seagulls.
Longitudinal CA will produce softness of image focus of perfectly on-axis objects because all colors in the spectrum will not come to focus at the same point.
Lateral CA will produce color fringes around all bright objects when viewed slightly off axis, but you should see a different color towards the lens center than you see towards the lens edge.
Quote: I've worked in the optical industry a bit, so I have a fair idea what the limiting factor in the quality of binoculars made for the mass market is.
Prisms aren't particularly easy to fabricate to really high levels of quality. The "quality sieve" method may help keep costs down, but they're still not cheap to make. (The "quality sieve" method of production was described to me by a fellow who had worked with the Japanese exporter of fine optics many years ago. A fabricator would make, say 1000 prisms, lens sets, whatever. Only the ones which met the higherst standards would be shipped to the most discriminating customer, say the best 200. The next 200 would be shipped to a customer who had high standards, but not so high as the "top dog", and so on, until the glass is all gone. The prisms that make it into the "no-name" binocs you buy at K-Mart for $19.95 likely came from the "bottom 200"!)
Quote: I suppose that z is the distance at which objects appear sharp to the naked eye at the same time that objects at infinity.
M is the binocular magnification
d is the distance at witch the binocular is perfectly focused.
Without accommodation of the eye, we can see objects perfectly sharp at the distance d'.
By definition, the depth of field is (d – d').
Now, if I suppose that the exit pupil is always larger than the eye pupil, I find the equation :
1/z = M².(1/d'-1/d)
.....So, the only optical parameter which determines depth of field is the magnification. Its influence is huge, because of the 2-power of M in the equation.
Now, why people find that binoculars with equal magnification have quite different depth of field ?
I think that the perceived depth of field in binoculars is determined by other parameters than optical ones.
Quote:focal length has almost none impact on the DOF. It is the magnification which dominates.
In summary it seems to be that only magnification and effective exit pupil are dominating factors for DOF. Focal length has some influence but not much. However, I am not sure how well the assumptions made for these calculations are satisfied. For example, a binocular is not made of thin lenses. Only professionals may be able to figure out the validity of these assumptions, maybe with the help of ray-tracing software.
Quote: The results can be found with the formula I wrote in a previous post :
1/z = M².(1/d'-1/d)
Here d is infinity, z=b , M=V and d'=G.
We have therefore : b=G/V² which is nearly the same as the formula on your post, in which the negligible terms have been omitted.
(For V=10 and G=100000 mm, we find b=1000 mm)
My formula is not rigorously exact, but is more general because it is also valid when the binoculars are not focused to infinity, but to the distance d.
I think it's worth doing some applications of this formula :
We suppose that the binoculars are focused to infinity, and that with naked eye we can see sharply objects without accommodation if they are 1 m away. Then DOF are :
For a 7x binocular : 49 m to infinity
For a 8x binocular : 64 m to infinity
For a 10x binocular : 100 m to infinity
For a 12x binocular : 144 m to infinity
People more than 60 years old, lacking in eye accommodation, and who have to rapidly focus between two distances (like birders), have to very carefully examine the drawbacks of high power binoculars, considering their poor depth of field.
Quote: This is your first stop for a comprehensive explanation of Binocular Summation, how binoculars, telescopes and telescope/Binoviewers all compare and the benefits that can be derived from each.
Binocular Vision Summation
This comprehensive thread includes a compilation of all I have written on Binocular Summation. In addition several noteworthy posts by other members add some imporant information on vision.
Northeastern State University College of Optometry, Tahlequah, OK
Vision Science course module by Thomas O. Salmon, OD, PhD
Vision Science Home
Salmon's Current Lectures
Old Lectures - Binocular Vision Series
Lecture 10 Binocular Summation
Predicting Binocular Visual Field Sensitivity from Monocular Visual Field Results
(Investigative Ophthalmology and Visual Science. 2000;41:2212-2221.)
© 2000 by The Association for Research in Vision and Ophthalmology, Inc.
Jacqueline M. Nelson-Quigg1, Kimberly Cello1 and Chris A. Johnson2
1 From the Optics and Visual Assessment Laboratory, Department of Ophthalmology, University of California, Davis; and 2 Discoveries in Sight Research Laboratories, Devers Eye Institute, Legacy Health Systems, Portland, Oregon.
Quote:I've learned what it means with telescopes that are Doublet and Triplet...but how is that terminology used for the 20x80 triplet bino's? are they true apo or semi-apo or something entirely different?
Quote: Lens Resolution Testing
and a link to a USAF 1951 Chart with the Table of Constants.
Chart with Table of Values
I find it interesting that few if any current web links provide ALL the information necessary to use these charts.
Using this table of values linked here which shows the constants for the Groups and Elements of the Line Pairs Chart,
the forumula is 8121 / (D x LPM) where D is the distance to your target measured in inches and LPM is the value from the Constants.
The constants are the actual number of line pairs per mm for the mimimum you can see.
For instance a 10x binocular used at a distance of 125 feet that can see line pairs in Group-1, Element2 has a value of 0.561. Therefore it's resolution is 8121/(125x12x0.561) = 9.65 arcseconds.
Line Pairs Resolution CANNOT be directly compared to point source resolution. See the forum discussion.
It is extremely important to have the target sized properly. See the discussion in the forum thread.
Binocular Resolution Testing Using 1951 USAF Line Pair Charts
included is a discussion on how to use the charts and links to web access for the charts and tables.
It is extremely important that the chart be exactly sized. As a check, the three bars and two spaces in Group-2 Element 1 should measure exactly 10mmx10mm. Both the sets of bars in G2-E2 and the solid black square top center should measure 9mmx9mm.
This page was originally accessed from
Lens Resolution Testing by Robert Monaghan
which has posted the following notation along with the information
[My understanding is that the USAF chart etc. is in the public domain as it is a government produced chart and related documentation...]