BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="Omid" data-source="post: 3444633" data-attributes="member: 16724">There are two topics that are being discussed in the neighboring thread (on Leica Nuctivid) which are interesting: Depth-of-Field and Light Transmission.On Depth of Field:I understand how depth of field for a camera lens can be defined (the object distances at which the lens produces a focus blur whose diameter is smaller than an acceptable threshold). In this case, DoF can be increased by limiting the aperture, effectively making the lens diameter smaller compare to focal length. Now, how can we define/measure depth of field for an afocal instrument such as binoculars? The eye, looking at the image formed by the objective through the eyepiece, can accommodate for some shift in image position so the DoF depends on the DoF of the eye. Doesn't it?By the way, what is wrong with shallow depth of field? It is a very useful feature in many occasions. It makes the subject pop-out against the background and is a key advantage of using binoculars in hunting (you can see through tress and brush etc.) Also, that's what makes all those wildlife photos taken using telephoto lenses very beautiful <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />On Brightness and Light Transmission:The usefulness of increasing light transmission of a binocular (isolated from reducing abberations, just thinking purely light transmission) is also highly questionable. The eye has a fantastic light intensity regulator so it will adjust to the proper brightness itself and in many many occasions, prefers reduced brightness (sunny day at beach, on a snow, etc). They human eye is not sensitive to small changes in brightness. Here is a cool test that everyone can do: look through your binoculars during the day and then position your index finger tip in front of the objective lens. See if you notice any changes in brightness <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" /> It is also interesting to know that one of the top optics brands manufactures a range-finding binoculars whose light transmission in one barrel is about 10% different than the other one (due to a semi-transparent mirror used to deflect laser light in one barrel). This is a successful product on the market and nobody notices the difference in light transmission <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" />The dynamic range of the eye is huge (Photopic vision: luminance levels over three candela per square meter; Scotopic vision: below 2 × 10−5 cd/m2; the ratio is 100,000 to one or more). So, I don't think that increasing the transmission of a binoculars from 90% to 95% has any advantage during all-around use of binoculars for birding or hunting (not considering astronomy here, that's different). Some Fresh Air:Here is some food for thought: Which vertical angle of gaze is the most comfortable angle for human eyes to look? If you need maximum visual acuity, were would you hold a picture or object? Would you hold it directly in front of your eyes? Would you hold it below your eye level? or would you hold it above your eye level?  Now, consider what your angle of gaze is when you use your binoculars for bird watching  <img src="data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7" class="smilie smilie--sprite smilie--sprite2" alt=";)" title="Wink    ;)" loading="lazy" data-shortname=";)" /></blockquote>

Verification