# How to determine a lens width?

• clalburn1420
In summary, the conversation discusses the concept of determining the width of a lens in order to focus an image at a specific distance on the other side. The focal length of the lens is determined by the shape of the lens and can be calculated using the equation 1/f = 1/u + 1/v. However, it is not possible to determine the shape of the lens using this equation. The conversation also mentions the possibility of placing an object directly on the lens to form an image, but this is not a recommended method. It is possible to focus an image at a distance of 3 cm on the other side if the focal length of the lens is correct, as demonstrated by the use of a microscope objective.
clalburn1420
I am wondering... say an object was put directly on a lens and you wanted the projected image to focus at around 3 cm on the other side. How do you determine how wide the lens has to be?

#### Attachments

• optbench.gif
5.1 KB · Views: 567
"how wide" in itself is not enough to specify this, since the angle of incedence depends on the curvature of the lens. you must look for a lens wth the correct focal length, where
1/f = 1/u + 1/v (if I'm remembering correctly)

http://hyperphysics.phy-astr.gsu.edu/hbase/geoopt/lenseq.html

Ah, so it is also determined by the shape. However, i expect it would need to be a convergent lens type and assume it needs to be like a () shaped lens. The problem is however, that this equation can help find focal length but not describe how the lens itself will be shaped.

Placing an object directly in contact with a lens (any lens) is not a good way to form an image any finite distance away from the lens. Why do you want to do this?

Simply curious if its possible. I'm not sure it is, which is why I'm wondering. What about if the object is a very small distance from the lens, like say 1 mm. Can you focus the image on the other side 3 cm away?

Sure, if the focal length of the lens is correct. That's how a microscope objective works.

## 1. How do I measure the lens width of my glasses?

To determine the lens width of your glasses, you will need a ruler or a measuring tape. Place one end of the ruler at the inner edge of one lens and measure across to the inner edge of the other lens. Make sure to measure in millimeters for accuracy.

## 2. Can I determine the lens width without taking off my glasses?

Yes, you can determine the lens width without taking off your glasses. Follow the same steps as mentioned above, but instead of measuring across both lenses, measure only one lens and double the measurement to get the total lens width.

## 3. What is the average lens width for eyeglasses?

The average lens width for eyeglasses is between 50-54mm, with 52mm being the most common. However, this can vary depending on personal preferences and the shape of one's face.

## 4. How does the lens width affect the fit of glasses?

The lens width is an important factor in determining the fit of glasses. A wider lens width may be more suitable for those with a broader face, while a narrower lens width may be better for those with a smaller face. It is important to find the right balance to ensure comfort and proper vision.

## 5. Are there any other measurements I should consider besides lens width?

Yes, besides lens width, you should also consider the bridge width and temple length when choosing glasses. The bridge width is the distance between the two lenses, and the temple length is the length of the arms that rest on your ears. These measurements, along with the lens width, make up the frame size and should be taken into consideration for a proper fit.

• Optics
Replies
10
Views
916
• Optics
Replies
8
Views
2K
• Optics
Replies
17
Views
2K
• Optics
Replies
19
Views
501
• Optics
Replies
58
Views
5K
• Optics
Replies
40
Views
3K
• Optics
Replies
77
Views
2K
• Optics
Replies
8
Views
2K
• Optics
Replies
1
Views
871
• Optics
Replies
9
Views
507