Optics and Light

It all depends on how far away the bird is.

Also, why are you trying to see the bird's eye? Are you going to fit it for glasses?

The building is a small dog house and the observer is standing next to it.

Solution: Bend over and look at the bird.

(Note: critical information missing can lead to misunderstandings.)

-A-

There are several ways to observe the "birds eye" view. Purchase a good spotters scope or a video camera with telescopic lens and digital enhancement. Otherwise attempting to build a quality scope from scratch will either be costly or take many hunrdeds of hours to create.

I built a telescope from scratch as a young boy. Several of my friends assisted me and it took days to weeks to grind and polish each lens. The result was just "okay" but it was the fact we actually accomplished the feat.

Buying the lenses and attempting to properly align the focal mechanism's, never mind the body structure and stands, can be just as hairy and costly. Cheaper and easier to buy one.

Try this.

-A-

Look i dunno how these telescopes are going to work unless you give some specifications

As far as i know, birds move and tilt their heads far more often than you'd like them to.

A telescope which takes too long to focus may not work here.

I have personally used high res digital photography or filming. It also keeps a record of other features such as angle of observation, type of bird, date, time, focus, distance etc etc. You can also tape your feet on the terrace or wherever it is that u are standing.

Hey if this dosent work for you, atleast you can make a buck by selling them to some nature magazine or discovery kids.

If the bird is on top of the building and you and your telescope are on the ground the only coloured eye you are going to see is brown. Unless of course the bird looks down to see who is looking up his/her kilt.

I am not familiar with the size of a bird's eye, but let's assume that it is 0.1 inch or 2.5 mm. At a distance of 100 m the eye would subtend an angle of 5.3 arc seconds (3600 seconds per degree).

The resolving power of a telescope is limited by the size of it's aperture. That is the objective lens in a refractor or the primary mirror in a reflecting telescope. We could discuss the resolving powere using diffraction theory. In a perfect telescope on a night with little atmospheric turbulance, one will observe a bright image with bright rings around it. The size of this central core limits the resolution of the telescope.

Insteat let's consider a binary star composed of 2 equally bright stars. The separation, a, which can be resolved can be approximated by

a = 4.5/A, where A is the aperture of the telescope in inches or

a = 114/A, where A is the aperture of the telescope in mm.

If you want 1 arc second resolution, you would need a telescope with an aperture of 114 mm. If one considers this 1 arc second as a "pixel", then there would be 4.5 pixels across the bird's eye.

Next, the human eye can resolve about 3 arc minutes. So to make the "pixel" large enough to see one would need 180 power of magnification.

Back to your question. The cheapest telescope would be a reflector. So buy or make one with a primary mirror at least 114 mm in diameter and procure an eyepiece (or eyepiece and Barlow lens) which would yield 180 power.