# I Steam punk, Field of view including the eye

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1. Dec 26, 2016

### George Albercook

Sorry if I missed the answer in my search. I expect I'm not use the correct terms. I want to design a Galilean/opera glasses style steampunk monical mounted to my reading glasses. I already have a simple lens that I can swing in front of my one eye.

When using commercial eyeglass mounted Galilean telescopes, like for dentists or surgeons, the image is too small. My impulse is to bring the object closer to make it bigger but then it is out of focus. The problem is that the image only fills a tiny fraction of the as image available to my eye. The field of view only describes the image seen through the optics.

By comparison, if I hold a simple magnifying lens, say 50 mm diameter, close to my eye, almost the entire field of view of my eye is filled with the image.

Is there another term for the percent of the eye's field of view that is filled with the image?

Thanks

2. Dec 26, 2016

### Staff: Mentor

The fraction of your vision filled with [the light from the telescope] depends only on the size of the telescope and how close to your eye it is.
The magnification then determines how large you see an object - a stronger magnification means small objects appear smaller, but your field of view (how far you can see to the sides) gets smaller as well.
Which one do you want to change?

3. Dec 26, 2016

### Andy Resnick

You are having trouble matching the image height of your compound lens system to the field of view of your eyeball. The focal length of the lens, in combination with it's physical diameter, tells you the angular field of view. For a single human eye, the angular field of view is about 60 degrees, this number is a combination of the small (instantatneous) field of view of the fovea and saccadic movements. So my guess is that the commercial device has too small a diameter.

There are other design considerations as well: the exit pupil of your compound lens should align with the entrance pupil of your eye, for example. And the image plane of your compound lens should be located at negative infinity (far in front of your eye), so you will view through the device with a relaxed eye.

http://www.edmundoptics.com/resourc...understanding-focal-length-and-field-of-view/

4. Dec 26, 2016

### Drakkith

Staff Emeritus
That was my thought as well. Widefield eyepieces for telescopes are absolutely massive compared to other eyepieces thanks to all the extra glass needed to form a high-quality, wide-field image. While you could probably use fewer elements for a trade off in image quality (which may not be noticeable if the magnification is relatively low), the final few elements still need to take up a large portion of the eye's field of view.

5. Dec 27, 2016

### Andy Resnick

Right- similarly, low power microscope eyepieces are significantly 'fatter' than high power eyepieces.