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Archives of an email list on the history of binoculars. - page 3 / 150





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  It's all done with mirrors as they say. All these prisms have the same basic optical geometry to perform the image erection as shown in the 1897 Hastings Patent, the variations are for improved manufacturing and reduced size.

  More photos and measured specs on the H-B binocular to come later.

  Steve Stayton    Tucson


  MIL-HDBK-141 is available on line, each chapter as a separate .pdf, adding up to about 90 megs:


  Or you can buy a reprint for $50. from Surplus Shed at


  Hastings & Brashear are two of the most important names in modern optics.  This patent has been known for some time, but the prototype model is a surprise.  A roof prism made in Pittsburgh, establishing precedent over the Abbe-Koenig prism, is quite interesting.     --Peter


Subject: Resolution

From: "randle dewees" <dewees@___.com>

>>>sharpness is a function of both resolution and contrast .....If  the  Zeiss glass is superior in both of these attributes, how can it be poorer in sharpness?<<<

  Some comments about resolution, contrast, and sharpness. Resolution and contrast are terms that are discussed and defined in many references on optics and optical instrumentation. Sharpness on the other hand has no technical definition that I'm aware of. It is a pedestrian term for a complex phenomenon, and as such is pretty useful in making a casual or general statement about the overall optical ability of an instrument to show things. The definitions of contrast and resolution are very specific about target contrast and spatial or frequency content. In a sense contrast and resolution are interchangeable at some scale. Combining the two properties, MTF provides a measure of contrast transfer at some image spatial frequency (resolution), or, somewhat conversely, spatial resolution at some contrast level. I think I'm safe in saying that a binocular that is really "sharp" has a MTF that is close to ideal, at least in the frequency range that means something to the human eye. So I'm agreeing with Arthur Tenenholtz's comment that sharpness is a function of resolution and contrast, and I also question the conclusions of that Astronomy article. Without measuring the MTF of binoculars any comparison is going to be subjective to some extent. Factors such as binocular weight, ergonomics, exit pupil correction, eye relief, distortion, flares and ghosts, will all influence the judgment of a casual evaluator.

  On another subject I received a Burgess 15/70 ($99) about two weeks ago. Overall a pretty powerful bino but it did have two problems. The more serious was a 4 arc-minute step error in collimation. I fixed this in a completely lucky fashion by removing and replacing one prism cover. I can probably look forward to future random changes in collimation but at least it's fixable (there are prism push screws, yuk). The other problem is the diopter adjustment is not balanced. My eyes are only 1/2 diopter apart yet I must screw the adjustable eyepiece almost all the way in. Bill Burgess offered to trade another pair but since they work for me I'm keeping them. I'll probably move the eyepiece in some fashion to help the matter (as an ex-Opticalman I know I should move the objective but that's not feasible on these binos). Otherwise, I like them - I certainly will not worry about them too much. There's not a lot of metal so they are easy to hold up - there are plastic parts and some of the metal is ridiculously thin. The eyepieces are incredibly good for the price, and "sharpness" is excellent in both barrels. These are multicoated on the outside surfaces and look to be fully MgF coated inside. . I'm really impressed with the optics, I have not used a auxiliary telescope to look at a point source but I bet the image will be more like a decent diffraction pattern than a aberrated blob.

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