Questions by shane91 - Page 23
Human Eye ModelExperiment 1: Optics of the Human Eye Part 2: Accommodation In the process of accommodation, muscles in the eye change the shape of the crystal- line lens to change its focal length. Initially, you will model accommodation by vary- ing the focal length of the crystalline lens using the adjustable focus lens. Later, when the model is filled with water, accommodation is achieved by replacing the crystalline lens with fixed lenses of various focal lengths. Procedure Note: If you have not done so yet, follow the instructions of page 5 to fill the adjustable focus lens with water. 1. Do not fill the eye model with water yet. Replace with lens in the SEPTUM slot with the adjustable focus lens. Position the eye model about 25 cm from the illu- minated screen Can you see the image on the retina? Move the syringe plunger to adjust the lens and form the clearest image possible. Is the lens concave or convex? Is it a converging lens or a diverging lens? 2. Move the eye model farther from the illuminated screen to about 50 cm. Adjust the lens again to form the clearest image. Did you increase or decrease the power of the lens? Did you increase or decrease the focal length? 3. Replace the adjustable focus lens with the +400 mm lens in the SEPTUM slot. Adjust the distance of the illuminated screen to form a clear image. Mark the position of the eye model so you can retum it to the same place after you fill it with water. 4. Fill the eye model with water to within 1 or 2 cm of the top. Return it to the same position as in step 3. Is the image still in focus? Try changing the distance, can you get it to focus? Explain what effect do the aqueous and vitreous humors (modeled by the water) have on the focal length of the eye's lens system? 5. Place the eye model about 35 cm from the light source, Replace the +400 mm lens in the SEPTUM slot with the +62 mm lens. Is the image in focus now? Move the eye model as close as possible to the light source while keeping the image in focus. Describe the image on the retina screen 6. Measure the object distance, o, from the screen of the light source to the top rim of the eye model, as pictured below. (The front of the rim is a convenient place to measure to and marks the center of the eye model's two-lens system.) Record this distance, which is the near point of the eye model when equipped with the +62 mm lens. The average human eye has a near point for distinct vision of about 25 cm tak +62 mm Lens