Cameras and Lenses

Beta Testing Elkcub's Binocular Brightness Simulator (EBBS)

My original post and several others were deleted. Although the discussion was extremely valuable, these deletions were made to prevent initial modeling assumptions from being mis-interpreted as facts.
Many thanks,
-elkcub

We dissagree about #1and #3. All other factors being equal (objective size and focal length, eyepiece focal length and light transmission efficiency) I believe the total amount of light energy that leaves the binocular's eyelens is proportional to the square of the diameter of the eyepiece fieldstop. For example: the total light energy allowed to pass by 10mm fieldstop=100, a 20mm fieldstop=400. However, the light intensity per unit of area for each field stop is the exactly same (the extra light energy in the form of extra field width that is allowed to pass to the eye by the larger field stop is masked by the edge of the smaller one, and so never reaches the eye). So IMO the width of the apparent field has no effect on light intensity per unit retinal area.

I suppose I would have to side with Stephen Ingraham about a mechanical system accurately predicting perceived brightness in actual binoculars. I've seen my share of over and underachievers, and besides it's just alot more fun to decide by really looking through the things.

Henry

[QUOTE=elkcub]Henry,

The total throughput efficiency of a binocular is the ratio of light output to light input. Nowadays that's between 50-90+% I'm told (by someone we know ). I've left room for an efficiency factor in EBBS. The light output leaves the exit pupil (which, I guess, is why they call it the "exit" pupil). If it goes through a small hole the intensity must be physically brighter (per unit area) than if it goes through a big hole. No?[/QUOTE]

Elk,

Yes, Henry said most of this already and for most forum members this must be very boring but here are my 2 eurocents worth...
I think the throughput efficiency is the ratio of light output/input like you said, but only in a narrow beam going through all the glass surfaces near the optical axis. The ratio of light output/total input would surely be much lower - I don't know how much though.

A binocular objective projects the image just under the eyepiece ("aerial image"), which is the maximal theoretical fov (determined by the focal length of the objective). The fieldstop is a hole, which cuts out the optically poor edges of the image and the eyepiece is a magnifying glass, which shows an enlarged image of this window. It is like watching a TV screen through different-sized windows - the image does not get brighter if you decrease the size of the window.

In a wide-angled binocular the photon intensity per unit area is higher in the *exit pupil*, but not in the projected image. On the retina this higher "brightness" is spread on a correspondingly larger area.

Ilkka

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